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21.01.2022
07:49 Arxiv.org Physics Fundamentals of Scanning Surface Structuring by Ultrashort Laser Pulses: From Electron Diffusion to Final Morphology. (arXiv:2201.08245v1 [physics.app-ph])

Industrial use of ultrashort-pulse surface structuring would significantly increase by an effective utilization of the average laser powers available currently. However, the unexplained degradation of surfaces processed with numerous pulses at high average laser power makes this difficult. Based on a systematic experimental study, the structure formation underlying such surface degradation was investigated. We presented a hierarchical structural formation model that bridges the gap between laser-induced periodic surface structures and surface degradation. Contrary to expectations based on previous research, we observed less structure formation on titanium for high laser fluences. As a possible reason, enhanced electron diffusion with increasing intensity was investigated within the framework of the two-temperature model. Our findings provide a deeper understanding of the microscopic mechanisms involved in surface structuring with ultrashort pulses.

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07:49 Arxiv.org Physics High-power laser experiment forming a supercritical collisionless shock in a magnetized uniform plasma at rest. (arXiv:2201.07976v1 [physics.plasm-ph])

We present a new experimental method to generate quasi-perpendicular supercritical magnetized collisionless shocks. In our experiment, ambient nitrogen (N) plasma is at rest and well-magnetized, and it has uniform mass density. The plasma is pushed by laser-driven ablation aluminum (Al) plasma. Streaked optical pyrometry and spatially resolved laser collective Thomson scattering clarify structures of plasma density and temperatures, which are compared with one-dimensional particle-in-cell simulations. It is indicated that just after the laser irradiation, the Al plasma is magnetized by self-generated Biermann battery field, and the plasma slaps the incident N plasma. The compressed external field in the N plasma reflects N ions, leading to counter-streaming magnetized N flows. Namely we identify the edge of the reflected N ions. Such interacting plasmas is forming a magnetized collisionless shock.

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07:49 Arxiv.org Physics Inner-shell excitation in the YbF molecule and its impact on laser cooling. (arXiv:2201.07871v1 [physics.atom-ph])

The YbF molecule is a sensitive system for measuring the electron's electric dipole moment. The precision of this measurement can be improved by direct laser cooling of the molecules to ultracold temperature. However, low-lying electronic states arising from excitation of a 4f electron may hinder laser cooling. One set of these "4f hole" states lies below the $A^2\Pi_{1/2}$ excited state used for laser cooling, and radiative decay to these intermediate levels, even with branching ratios as small as $10^{-5}$, can be a hindrance. Other 4f hole states lie very close to the $A^2\Pi_{1/2}$ state, and a perturbation results in states of mixed character that are involved in the laser cooling cycle. This perturbation may enhance the loss of molecules to states outside of the laser cooling cycle. We model the perturbation of the $A^2\Pi_{1/2}$ state to determine the strength of the coupling between the states, the de-perturbed potential energy curves, and the radiative branching ratios to

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07:14 News-Medical.Net Laser-driven needle-free injection is more effective and safer than previous technologies

Fear of needles is, for part of the population, the main reason for not having a Covid-19 vaccine. That fear is of all times, clearly demonstrated by the fact that needleless techniques have been developed for over 150 years.

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20.01.2022
18:34 Phys.org Stirring a superfluid with a laser

Scientists from the Graduate School of Engineering Science at Osaka University used optical tweezers for the first time inside superfluid helium. With a strongly focused beam of light, they demonstrated the stable trapping of nanoparticles at ultralow temperatures. This work may help scientists better understand the conceptual boundary that separates classical and quantum effects.

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10:26 Arxiv.org Physics Tunneling ionization in ultrashort laser pulses: edge-effect and remedy. (arXiv:2201.07589v1 [physics.atom-ph])

Tunneling ionization of an atom in ultrashort laser pulses is considered. When the driving laser pulse is switched-on and -off with a steep slope, the photoelectron momentum distribution (PMD) shows an edge-effect because of the photoelectron diffraction by the time-slit of the pulse. The trivial diffraction pattern of the edge effect consisting of fast oscillations in the PMD disguises in the deep nonadiabatic regime the physically more interesting features in the spectrum which originate from the photoelectron dynamics. We point out the precise conditions how to avoid this scenario experimentally and if unavoidable in theory we put forward an efficient method to remove the edge-effect in the PMD. This allows to highlight the nonadiabatic dynamical features of the PMD, which is indispensable for their further investigation in complex computationally demanding scenarios. The method is firstly demonstrated on a one-dimensional problem, and further applied in three-dimensions for the

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10:26 Arxiv.org Physics On the delayed emission from laser produced aluminum plasma under argon environment. (arXiv:2201.07497v1 [physics.plasm-ph])

In this article, we report rather long time emission ($\sim$ 250 $\mu$s) from aluminum neutrals (Al I) in ns laser produced plasma in the presence of ambient argon. The study is carried out with varying laser intensity, background pressure, and distance from the target. Slow and fast peaks components in the emission spectra observed at earlier times are well reported. However, interestingly a very long delayed emission is also observed for the first time which depends on laser intensity, distance from the target, ambient gas, and pressure. The emission is observed from Al neutrals only. The most likely mechanism of this emission appears to be the excitation and subsequent emission from Al neutrals as a result of energy transfer from metastables of the ambient gas.

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10:26 Arxiv.org Physics Frequency Stability Transfer in Passive Mode-Locked Quantum-dash Laser Diode using Optical Injection Locking. (arXiv:2201.07467v1 [physics.optics])

In this paper, we present an experimental study of the metrological stabilization of a solid-state frequency comb for embedded metrology applications. The comb is a passively mode-locked laser diode based on InGaAs/InP Quantum-dash structure emitting optical lines into a 9 nm bandwidth centered at 1.55 $\mu$m with a repetition rate of 10.09 GHz. The frequency stabilization is achieved by optical injection locking of the comb with an external cavity laser diode referenced onto a metrological frequency standard. One observes the transfer of the spectral purity from the injection laser to the neighbouring modes of the injected one as well as the transfer of stability to the adjacent modes. The measurement of the long term stability highlights a frequency noise with random walk behavior specific of the passive mode locking process. Demonstration of sidebands of the injection laser at the repetition frequency of the comb also makes it possible to propose a transfer mechanism and to consider

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19.01.2022
19:01 Phys.org Advanced algorithms plus exceptional X-ray laser reveal structures of not-so-neat-and-tidy materials

Francis Crick, who famously co-discovered the shape of DNA, once said: "If you want to understand function, study structure." Many decades later, this remains a tenet of biology, chemistry, and materials science.

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06:14 Arxiv.org CS Mixed Diagnostics for Longitudinal Properties of Electron Bunches in a Free-Electron Laser. (arXiv:2201.05769v1 [physics.acc-ph])

Longitudinal properties of electron bunches are critical for the performance of a wide range of scientific facilities. In a free-electron laser, for example, the existing diagnostics only provide very limited longitudinal information of the electron bunch during online tuning and optimization. We leverage the power of artificial intelligence to build a neural network model using experimental data, in order to bring the destructive longitudinal phase space (LPS) diagnostics online virtually and improve the existing current profile online diagnostics which uses a coherent transition radiation (CTR) spectrometer. The model can also serve as a digital twin of the real machine on which algorithms can be tested efficiently and effectively. We demonstrate at the FLASH facility that the encoder-decoder model with more than one decoder can make highly accurate predictions of megapixel LPS images and coherent transition radiation spectra concurrently for electron bunches in a bunch train with

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06:03 Arxiv.org Physics Laser Cooling Beyond Rate Equations: Approaches From Quantum Thermodynamics. (arXiv:2201.07132v1 [quant-ph])

Solids can be cooled by driving impurity ions with lasers, allowing them to transfer heat from the lattice phonons to the electromagnetic surroundings. This exemplifies a quantum thermal machine, which uses a quantum system as a working medium to transfer heat between reservoirs. We review the derivation of the Bloch-Redfield equation for a quantum system coupled to a reservoir, and its extension, using counting fields, to calculate heat currents. We use the full form of this equation, which makes only the weak-coupling and Markovian approximations, to calculate the cooling power for a simple model of laser cooling. We compare its predictions with two other time-local master equations: the secular approximation to the full Bloch-Redfield equation, and the Lindblad form expected for phonon transitions in the absence of driving. We conclude that the full Bloch-Redfield equation provides accurate results for the heat current in both the weak- and strong- driving regimes, whereas the other

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06:03 Arxiv.org Physics Precision laser diagnostics for LUXE. (arXiv:2201.06925v1 [physics.ins-det])

Strong field QED is an active research frontier. The investigation of fundamental phenomena such as pair creation, photon-photon and photon-electron interactions in the nonlinear QED regime are a formidable challenge -- both experimentally and theoretically. Several experiments around the world are being planned or in preparation to probe this strong field regime. LUXE (Laser Und XFEL Experiment) is an experimental platform which envisages the collision of the high quality 16.5 GeV electron beam from the European XFEL accelerator with a 100 TW class high power laser. One of the unique features of LUXE is to measure the key observables such as pair rates ($e^+e^-$) with unprecedented accuracy in the characterization of both beams together with ample statistics. The state-of-art detector technologies for high energy particle and photon detection enable percent level precision. The state-of-art high power lasers offer high quality laser beams, however, the residual shot-to-shot

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06:03 Arxiv.org Physics Laser ion acceleration from tailored solid targets with micron-scale channels. (arXiv:2201.06549v1 [physics.plasm-ph])

Laser ion acceleration is a promising concept for generation of fast ions using a compact laser-solid interaction setup. In this study, we theoretically investigate the feasibility of ion acceleration from the interaction of petawatt-scale laser pulses with a structured target that embodies a micron-scale channel filled with relativistically transparent plasma. Using 2D and 3D Particle-In-Cell (PIC) simulations and theoretical estimates, we show that it is possible to generate GeV protons with high volumetric charge and quasi-monoenergetic feature in the energy spectrum. We interpret the acceleration mechanism as a combination of Target Normal Sheath Acceleration and Radiation Pressure Acceleration. Optimal parameters of the target are formulated theoretically and verified using 2D PIC simulations. 3D PIC simulations and realistic preplasma profile runs with 2D PIC show the feasibility of the presented laser ion acceleration scheme for the experimental implementation at the currently

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06:03 Arxiv.org Physics Nondipole effects in tunneling ionization by intense laser pulses. (arXiv:2201.06264v1 [physics.atom-ph])

The limit of decreasing laser frequency can not be considered independently from nondipole effects due to increase in the laser-induced continuum electron speed in this limit. Therefore, in this work, tunneling ionization in the adiabatic limit is considered for an effective field that includes effects beyond the electric-dipole term to first order in $1/c$, with $c$ the speed of light. The nondipole term describes the interaction resulting from the electric dipole-induced velocity of the electron and the magnetic field component of the laser. The impact of this term on the ionization rate, tunnel exit point, momentum at the tunnel exit and electron dynamics is discussed. In the appropriate limit, the results of a nondipole strong-field approximation approach and those of the strict adiabatic limit, where time and field strength are parameters, are consistent. The nondipole strong-field approximation approach is used to identify nonadiabatic modifications of the initial conditions. The

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06:03 Arxiv.org Physics Mixed Diagnostics for Longitudinal Properties of Electron Bunches in a Free-Electron Laser. (arXiv:2201.05769v1 [physics.acc-ph])

Longitudinal properties of electron bunches are critical for the performance of a wide range of scientific facilities. In a free-electron laser, for example, the existing diagnostics only provide very limited longitudinal information of the electron bunch during online tuning and optimization. We leverage the power of artificial intelligence to build a neural network model using experimental data, in order to bring the destructive longitudinal phase space (LPS) diagnostics online virtually and improve the existing current profile online diagnostics which uses a coherent transition radiation (CTR) spectrometer. The model can also serve as a digital twin of the real machine on which algorithms can be tested efficiently and effectively. We demonstrate at the FLASH facility that the encoder-decoder model with more than one decoder can make highly accurate predictions of megapixel LPS images and coherent transition radiation spectra concurrently for electron bunches in a bunch train with

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06:03 Arxiv.org Physics Modelling heat transfer in laser-soft matter interaction via chaotic Ikeda map. (arXiv:2201.05682v1 [physics.med-ph])

We develop a model for simulating the heat transfer phenomena within a biological soft material using the Ikeda chaotic map. Our approach is implemented by sampling the optical intensity via the Ikeda map to investigate the influence on the heat distribution over the tissue. Our method has many potential advantages including the possibility of investigating the nonlinear optical effects resulting from the intense beam-induced feedback mechanisms. This in turn, leads to the flexibility and dynamical controllability in comparison to the quasi-static Monte-Carlo method. The proposed approach is thus appropriate for the applications in the light beam-guided nanodrug injection and microsurgery.

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17.01.2022
19:30 NewYork Times A California City Is Overrun by Crows. Could a Laser Be the Answer?

In a move befitting its Silicon Valley setting, the city of Sunnyvale, Calif., will aim a laser at 1,000 birds that have overwhelmed the downtown area during the pandemic.

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02:44 Ixbt.com На выпуск проектора для домашнего кинотеатра Nebula Cosmos Laser 4K уже собрано более 2,3 млн долларов

Создатели проектора для домашнего кинотеатра Nebula Cosmos Max, на выпуск которого в 2019 году было собрано более 1,5 млн долларов, превзошли свой результат с новым устройством той же категории. На выпуск проектора Nebula Cosmos Laser 4K уже собрано около 2,35 млн долларов. И это далеко не окончательная сумма, потому что сбор средств будет продолжаться еще 39 дней. По словам разработчиков, это самый компактный лазерный проектор 4K. Он создает световой поток 2400 лм и может формировать изображение размером до 150 дюймов по диагонали. Проектор с Android TV 10.0 поддерживает HDR10. Он оснащен звуковым процессором, усилителем, двумя широкополосными динамиками мощностью по 10 Вт и двумя высокочастотными динамиками мощностью по 5 Вт. Конечно, есть функции коррекции трапецеидальных искажений и автоматической фокусировки. В описании также упомянута поддержка Chromecast, AiFi Technology и Dolby Audio. Конфигурация устройства включает однокристальную систему с четырехъядерным

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14.01.2022
21:19 NewScientist.Com Portable laser scanner creates colour 3D images of surfaces or objects

Lidar uses lasers to create 3D images, but these can be hard to interpret because they are black and white. A new scanner adds cameras to make colour images that could be useful for infrastructure inspection or robot vision

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05:29 Arxiv.org Physics Mode conversion and laser energy absorption by plasma under an inhomogeneous external magnetic field. (arXiv:2201.04926v1 [physics.plasm-ph])

The interaction of a high-frequency laser with plasma in the presence of an inhomogeneous external magnetic field has been studied here with the help of Particle-In-Cell simulation. It has been shown that laser enters inside the plasma as an extraordinary wave (X-wave), where the electric field of the wave oscillates perpendicular to both external magnetic field and propagation direction, and as it travels through the plasma, its dispersion property changes due to the inhomogeneity of the externally applied magnetic field. Our study shows that the X-wave's electromagnetic energy is converted to an electrostatic mode as it encounters the upper-hybrid (UH) resonance layer. In the later stage of the evolution, this electrostatic wave breaks and converts its energy to electron kinetic energy. Our study reveals two additional processes involved in decaying electrostatic mode at the UH resonance layer. We have shown that the energy of the electrostatic mode also converts to a low-frequency

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05:29 Arxiv.org Physics Simulations of the filamentation and self-channeling of spatially modulated high-power femtosecond laser pulses in air. (arXiv:2201.04783v1 [physics.optics])

The propagation of high-power femtosecond laser pulses in air under conditions of superposed spatial phase modulation is considered theoretically. The numerical simulations are carried out on the basis of the reduced form of nonlinear Schrodinger equation (NLSE) for time-averaged electric field envelope. Initial spatial modulations are applied to pulse wavefront profiling by a staggered (TEM33) phase plate which is simulated numerically. The dynamics of laser pulse self-focusing, filamentation, and post-filamentation self-channeling after the phase plates with variable phase jumps is studied. We show that with specific phase modulations, the pulse filamentation region in air can be markedly shifted further and elongated compared to a non-modulated pulse. Moreover, during the post-filamentation propagation of spatially structured radiation, the highly-localized light channels are formed possessing enhanced intensity and reduced angular divergence which enables post-filamentation pulse

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13.01.2022
08:06 Arxiv.org Physics Impact of FBG feedback phase on laser dynamics. (arXiv:2201.04497v1 [physics.optics])

Fiber Bragg Gratings have been advantageously used to improve the chaotic properties of semiconductor lasers. Though these components are known to be highly sensitive to environmental conditions, feedback phase fluctuations are often neglected. In this work, we experimentally demonstrate that the small variations of the propagation time induced by a simple thermal tuning of the FBG is sufficient to induce significant changes of the laser behavior. We report periodic stability enhancements linked with phase variations and highlight that both phase variation and phase offsets play an important role. Last, we show a good qualitative agreement with simulations based on an expanded version of the Lang-Kobayashi model.

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08:06 Arxiv.org Physics Ridge polariton laser: different from a semiconductor edge-emitting laser. (arXiv:2201.04348v1 [physics.optics])

We experimentally demonstrate the difference between a ridge polariton laser, and a conventional edge-emitting ridge laser operating under electron-hole population inversion. The horizontal laser cavities are 20 -- 60 $\mu$m long GaN etched ridge structures with vertical Bragg reflectors. We investigate the laser threshold under optical pumping and assess quantitatively the effect of a varying optically-pumped length. The laser effect is achieved for an exciton reservoir length of just 15% of the cavity length, which would not be possible in a conventional ridge laser, with an inversion-less polaritonic gain about 10 times larger than in equivalent GaN lasers. The modelling of the cavity free spectral range demonstrates the polaritonic nature of the modes.

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07:11 Arxiv.org Quantitative Biology Inferring characteristics of bacterial swimming in biofilm matrix from time-lapse confocal laser scanning microscopy. (arXiv:2201.04371v1 [q-bio.QM])

Biofilms are spatially organized microorganism colonies embedded in a self-produced matrix, conferring to the microbial community resistance to environmental stresses. Motile bacteria have been observed swimming in the matrix of pathogenic exogeneous host biofilms. This observation opened new promising routes for deleterious biofilms biocontrol: these bacterial swimmers enhance biofilm vascularization for chemical treatment or could deliver biocontrol agent by microbial hitchhiking or local synthesis. %\cite{muok2021microbial,yu2020hitchhiking,samad2017swimming}. Hence, characterizing swimmer trajectories in the biofilm matrix is of particular interest to understand and optimize its biocontrol.In this study, a new methodology is developed to analyze time-lapse confocal laser scanning images to describe and compare the swimming trajectories of bacterial swimmers populations and their adaptations to the biofilm structure. The method is based on the inference of a kinetic model of swimmer

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12.01.2022
10:40 Arxiv.org Physics Electrically pumped blue laser diodes with nanoporous bottom cladding. (arXiv:2201.03939v1 [physics.app-ph])

We demonstrate electrically pumped III-nitride edge-emitting laser diodes (LDs) with nanoporous bottom cladding. The LD structure was grown by plasma-assisted molecular beam epitaxy. Highly doped 350 nm thick GaN:Si cladding layer with Si concentration of 6 x 1019 cm-3 was electrochemically etched to obtain porosity of 15 +/- 3% with pore size of 20 +/- 9 nm. The devices with nanoporous bottom cladding are compared to the refer-ence structures. The pulse mode operation was obtained at 448.7 nm with a slope efficiency (SE) of 0.2 W/A while the reference device without etched cladding layer was lasing at 457 nm with SE of 0.56 W/A. The de-sign of the LDs with porous bottom cladding was modelled theoretically. Performed calculations allowed to choose the optimum porosity and thickness of the cladding needed for the desired optical mode confinement and reduced the risk of light leakage to the substrate and to the top-metal contact. This demonstration opens new possibilities for the

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10:40 Arxiv.org Physics Studying the operation of an all-PM Yb-doped fiber laser oscillator at negative and positive net cavity dispersion. (arXiv:2201.03870v1 [physics.optics])

Chirped fiber Bragg gratings in Yb-doped fiber lasers allow tuning the net cavity dispersion, thus enabling access to pulse dynamics beyond the typical all-normal-dispersion dissipative soliton regime. This Letter demonstrates an ultrafast dispersion-managed all-polarization-maintaining fiber oscillator mode-locked with a nonlinear optical loop mirror. Using a chirped fiber Bragg grating inside the oscillator, it can work at net cavity dispersion in the range from -0.098 ps$^2$ up to +0.067 ps$^2$ and above at the wavelength of 1 $\mathrm{\mu}$m. Depending on the configuration, the system can deliver stable pulses with energies up to 2.3 nJ and pulse durations as short as 98 fs.

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11.01.2022
06:09 Arxiv.org Physics Experimental observations of detached bow shock formation in the interaction of a laser-produced plasma with a magnetized obstacle. (arXiv:2201.03520v1 [physics.plasm-ph])

The magnetic field produced by planets with active dynamos, like the Earth, can exert sufficient pressure to oppose supersonic stellar wind plasmas, leading to the formation of a standing bow shock upstream of the magnetopause, or pressure-balance surface. Scaled laboratory experiments studying the interaction of an inflowing solar wind analog with a strong, external magnetic field are a promising new way to study magnetospheric physics and to complement existing models, although reaching regimes favorable for magnetized shock formation is experimentally challenging. This paper presents experimental evidence of the formation of a magnetized bow shock in the interaction of a supersonic, super-Alfv\'enic plasma with a strongly magnetized obstacle at the OMEGA laser facility. The solar wind analog is generated by the collision and subsequent expansion of two counter-propagating, laser-driven plasma plumes. The magnetized obstacle is a thin wire, driven with strong electrical currents.

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06:09 Arxiv.org Physics Perspective: Ultrafast imaging of molecular dynamics using ultrafast low-frequency lasers, x-ray free electron laser and electron pulses. (arXiv:2201.03197v1 [physics.atom-ph])

The requirement of high space-time resolution and brightness is a great challenge for imaging atomic motion and making molecular movies. Important breakthroughs in ultrabright tabletop laser, x-ray and electron sources have enabled the direct imaging of evolving molecular structures in chemical processes.And recent experimental advances in preparing ultrafast laser and electron pulses equipped molecular imaging with femtosecond time resolution. This Perspectives present an overview of versatile imaging methods of molecular dynamics.High-order harmonic generation imaging maps the harmonic order of photons to the time delay for nuclear motion and can reach attosecond time resolution. Coulomb explosion imaging retrieves molecular structural information by detecting the momentum vectors of fragmented ions. Diffraction imaging encodes molecular structural and electronic information in reciprocal space, achieving high spatial resolution by using x-ray or electrons with short wavelengths. The

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06:09 Arxiv.org Physics Control of electron beam polarization in the bubble regime of laser-wakefield acceleration. (arXiv:2201.02969v1 [physics.plasm-ph])

Electron beam polarization in the bubble regime of the interaction between a high-intensity laser and a longitudinally pre-polarized plasma is investigated by means of the Thomas-Bargmann-Michel-Telegdi equation. Using a test-particle model, the dependence of the accelerated electron polarization on the bubble geometry is analyzed in detail. Tracking the polarization dynamics of individual electrons reveals that although the spin direction changes during both the self-injection process and acceleration phase, the former has the biggest impact. For nearly spherical bubbles, the polarization of electron beam persists after capture and acceleration in the bubble. By contrast, for aspherical bubble shapes, the electron beam becomes rapidly depolarized, and the net polarization direction can even reverse in the case of a oblate spheroidal bubble. These findings are confirmed via particle-in-cell simulations.

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06:09 Arxiv.org Physics Progress toward a microwave frequency standard based on laser-cooled large scale 171Yb+ ion crystal. (arXiv:2201.02937v1 [physics.atom-ph])

We report on progress towards a microwave frequency standard based on a laser-cooled 171Yb+ ion trap system. The electronics, lasers, and magnetic shields are integrated into a single physical package. With over 1E5 ions are stably trapped, the system offers a high signal-to-noise ratio Ramsey line-shape. In comparison with previous work, the frequency instability of a 171Yb+ microwave clock was further improved to $8.5 \times {10^{ - 13}}/\sqrt \tau$ for averaging times between 10 and 1000 s.

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06:09 Arxiv.org Physics The influence of laser characteristics on internal flow behaviour in laser melting of metallic substrates. (arXiv:2201.02614v1 [physics.flu-dyn])

The absorptivity of a material is a major uncertainty in numerical simulations of laser welding and additive manufacturing, and its value is often calibrated through trial-and-error exercises. This adversely affects the capability of numerical simulations when predicting the process behaviour and can eventually hinder the exploitation of fully digitised manufacturing processes, which is a goal of "industry 4.0". In the present work, an enhanced absorption model that takes into account the effects of laser characteristics, incident angle, surface temperature, and material composition is utilised to predict internal heat and fluid flow in laser melting of stainless steel 316L. Employing such an absorption model is physically more realistic than assuming a constant absorptivity and can reduce the costs associated with calibrating an appropriate value. High-fidelity three-dimensional numerical simulations were performed using both variable and constant absorptivity models and the

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10.01.2022
18:54 Technology.org Closer to the perfect laser

Ultra-precise lasers can be used for optical atomic clocks, quantum computers, power cable monitoring, and much more. But

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09:21 Arxiv.org CS Charging Techniques for UAV-assisted Data Collection: Is Laser Power Beaming the Answer?. (arXiv:2201.02573v1 [cs.NI])

As Covid-19 has increased the need for connectivity around the world, researchers are targeting new technologies that could improve coverage and connect the unconnected in order to make progress toward the United Nations Sustainable Development Goals. In this context, drones are seen as one of the key features of 6G wireless networks that could extend the coverage of previous wireless network generations. That said, limited on-board energy seems to be the main drawback that hinders the use of drones for wireless coverage. Therefore, different wireless and wired charging techniques, such as laser beaming, charging stations, and tether stations are proposed. In this paper, we analyze and compare these different charging techniques by performing extensive simulations for the scenario of drone-assisted data collection from ground-based Internet of Things (IoT) devices. We analyze the strengths and weaknesses of each charging technique, and finally show that laser-powered drones strongly

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08:47 Arxiv.org Physics Laser-Driven, Ion-Scale Magnetospheres in Laboratory Plasmas. II. Particle-in-cell Simulations. (arXiv:2201.02416v1 [physics.plasm-ph])

Ion-scale magnetospheres have been observed around comets, weakly-magnetized asteroids, and localized regions on the Moon, and provide a unique environment to study kinetic-scale plasma physics, in particular in the collisionless regime. In this work, we present the results of particle-in-cell simulations that replicate recent experiments on the Large Plasma Device at the University of California, Los Angeles. Using high-repetition rate lasers, ion-scale magnetospheres were created to drive a plasma flow into a dipolar magnetic field embedded in a uniform background magnetic field. The simulations are employed to evolve idealized 2D configurations of the experiments, study highly-resolved, volumetric datasets and determine the magnetospheric structure, magnetopause location and kinetic-scale structures of the plasma current distribution. We show the formation of a magnetic cavity and a magnetic compression in the magnetospheric region, and two main current structures in the dayside of

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07.01.2022
09:44 Arxiv.org Physics Laser-Driven, Ion-Scale Magnetospheres in Laboratory Plasmas. I. Experimental Platform and First Results. (arXiv:2201.02176v1 [physics.plasm-ph])

Magnetospheres are a ubiquitous feature of magnetized bodies embedded in a plasma flow. While large planetary magnetospheres have been studied for decades by spacecraft, ion-scale "mini" magnetospheres can provide a unique environment to study kinetic-scale, collisionless plasma physics in the laboratory to help validate models of larger systems. In this work, we present preliminary experiments of ion-scale magnetospheres performed on a unique high-repetition-rate platform developed for the Large Plasma Device (LAPD) at UCLA. The experiments utilize a high-repetition-rate laser to drive a fast plasma flow into a pulsed dipole magnetic field embedded in a uniform magnetized background plasma. 2D maps of magnetic field with high spatial and temporal resolution are measured with magnetic flux probes to examine the evolution of magnetosphere and current density structures for a range of dipole and upstream parameters. The results are further compared to 2D PIC simulations to identify key

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09:44 Arxiv.org Physics Dual-laser self-injection locking to an integrated microresonator. (arXiv:2201.02130v1 [physics.optics])

Diode laser self-injection locking (SIL) to a whispering gallery mode of a high quality factor resonator is a widely used method for laser linewidth narrowing and high-frequency noise suppression. SIL has already been used for the demonstration of ultra-low-noise photonic microwave oscillators and soliton microcomb generation and has a wide range of possible applications. Up to date, SIL was demonstrated only with a single laser. However, multi-frequency and narrow-linewidth laser sources are in high demand for modern telecommunication systems, quantum technologies, and microwave photonics. Here we experimentally demonstrate the dual-laser SIL of two multifrequency laser diodes to different modes of an integrated Si$_3$N$_4$ microresonator. Simultaneous spectrum collapse of both lasers, as well as linewidth narrowing and high-frequency noise suppression , as well as strong nonlinear interaction of the two fields with each other, are observed. Locking both lasers to the same mode

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09:44 Arxiv.org Physics Generating asymmetric aberration laser beams with controlled intensity distribution. (arXiv:2201.02036v1 [physics.optics])

We present generation of asymmetric aberration laser beams (aALBs) with controlled intensity distribution, using a diffractive optical element (DOE) involving phase asymmetry. The asymmetry in the phase distribution is introduced by shifting the coordinates in a complex plane. The results show that auto-focusing properties of aALBs remain invariant with respect to the asymmetry parameters. However, a controlled variation in the phase asymmetry allows to control the spatial intensity distribution of aALBs. In an ideal ALB containing equal intensity three bright lobes (for $m=3$), by introducing asymmetry most of the intensity can be transferred to any one of single bright lobe, and forms a high-power density lobe. A precise spatial position of high-power density lobe can be controlled by the asymmetry parameter $\beta$ and $m$, and we have determined the empirical relations for them. We have found that for the specific values of $\beta$, the intensity in the high-power density lobe can

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09:44 Arxiv.org Physics High fill factor confocal compound eyes fabricated by direct laser writing for better imaging quality. (arXiv:2201.01915v1 [physics.optics])

We fabricate two kinds of 100% fill factor compound eye structures using direct laser writing, including conventional compound eyes (CVCEs) with the same focal length of each microlens unit, and specially designed confocal compound eyes (CFCEs). For CFCEs, the focal length of each microlens unit is determined by its position and is equal to the distance between the microlens unit and the image sensor. In this letter, the optical properties of CVCEs and CFCEs are tested and compared. It is found that compared with CVCEs, CFCEs can improve the focusing efficiency by about 7%, enlarge the imaging area by about 25%, and have better imaging quality at the edge of the field of view.

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06.01.2022
16:23 Phys.org Improving the conductivity of metal nanoelectrodes achieved via plasmon-enhanced laser nanosoldering

In a new publication from Opto-Electronic Advances, the research groups of Professor Xuan-Ming Duan from Jinan University Guangzhou, China and Professor Mei-Ling Zheng from the Institute of Physics and Chemistry of Chinese Academy of Sciences, Beijing, China discuss plasmon-enhanced nanosoldering of silver nanoparticles for high-conductive nanowires electrodes.

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10:03 Ixbt.com Компанией Kyocera SLD Laser установлен мировой рекорд скорости передачи данных по LiFi — в 100 раз выше скорости 5G

Kyocera SLD Laser (KSLD), дочерняя компания корпорации Kyocera, занимающаяся коммерциализацией нового поколения лазерных источников света на основе нитрида галлия для автомобилей, мобильных устройств, осветительных приборов и потребительской электроники, объявила о создании самой быстрой в мире системы LiFi. Обеспечивая скорость передачи данных более 90 Гбит/с, эта система в 100 раз превосходит по этому параметру технологию 5G. В эти дни разработчик демонстрирует систему DataLight, предназначенную для автомобильных и потребительских приложений на выставке CES 2022. «Мы очень рады объявить о достижении KSLD мирового рекорда скорости передачи данных LiFi 90 Гбит/с и о демонстрации этой инновации DataLight на выставке CES 2022 на нашем выставочном стенде, — заявил Джеймс Рэринг (James Raring), генеральный директор Kyocera SLD Laser. — Наша сверхвысокоскоростная технология LiFi — это первопроходец в области освещения и беспроводной связи, она безопасна для

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05:55 Arxiv.org CS Robotic Laser Orientation Planning with a 3D Data-driven Method. (arXiv:2201.01401v1 [cs.RO])

This paper focuses on a research problem of robotic controlled laser orientation to minimize errant overcutting of healthy tissue during the course of pathological tissue resection. Laser scalpels have been widely used in surgery to remove pathological tissue targets such as tumors or other lesions. However, different laser orientations can create various tissue ablation cavities, and incorrect incident angles can cause over-irradiation of healthy tissue that should not be ablated. This work aims to formulate an optimization problem to find the optimal laser orientation in order to minimize the possibility of excessive laser-induced tissue ablation. We first develop a 3D data-driven geometric model to predict the shape of the tissue cavity after a single laser ablation. Modelling the target and non-target tissue region by an obstacle boundary, the determination of an optimal orientation is converted to a collision-minimization problem. The goal of this optimization formulation is

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05:19 Arxiv.org Physics Insensitivity of a turbulent laser-plasma dynamo to initial conditions. (arXiv:2201.01705v1 [physics.plasm-ph])

It has recently been demonstrated experimentally that a turbulent plasma created by the collision of two inhomogeneous, asymmetric, weakly magnetised laser-produced plasma jets can generate strong stochastic magnetic fields via the small-scale turbulent dynamo mechanism, provided the magnetic Reynolds number of the plasma is sufficiently large. In this paper, we compare such a plasma with one arising from two pre-magnetised plasma jets whose creation is identical save for the addition of a strong external magnetic field imposed by a pulsed magnetic field generator (`MIFEDS'). We investigate the differences between the two turbulent systems using a Thomson-scattering diagnostic, X-ray self-emission imaging and proton radiography. The Thomson-scattering spectra and X-ray images suggest that the presence of the external magnetic field has a limited effect on the plasma dynamics in the experiment. While the presence of the external magnetic field induces collimation of the flows in the

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05:19 Arxiv.org Physics Ultralow-threshold green fluorescent protein laser based on high Q microbubble resonators. (arXiv:2201.01425v1 [physics.optics])

Biological lasers have attracted vast attention because of their potential medical application prospects, especially the low threshold biological laser, which can be used for ultrasensitive biological detection while ensuring that its luminous gain medium is not damaged by the high-energy pump light. By coupling the low concentration green fluorescent protein (GFP) solution with a high Q whispering gallery mode microbubble resonator, we managed to fabricate a miniature GFP laser with ultralow lasing threshold of 500 nJ/mm^2. The energy used to excite the GFP can be reduced to 380 fJ, two orders of magnitude lower than that of the lowest excitation energy GFP laser known. The Q value of the optical cavity in this biological laser is 5.3 x 10^7, the highest among GFP lasers at present. We further confirmed the long-term stability of the working characteristics of GFP laser for the first time and found that its optical characteristics can be maintained for at least 23 days. Finally, we

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05.01.2022
07:54 Arxiv.org Physics Laser Driven Nuclear physics at ELINP. (arXiv:2201.01068v1 [physics.ins-det])

High power lasers have proven being capable to produce high energy gamma rays, charged particles and neutrons to induce all kinds of nuclear reactions. At ELI, the studies with high power lasers will enter for the first time into new domains of power and intensities.

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04.01.2022
10:19 Arxiv.org Physics Design of a rapid transit to Mars mission using laser-thermal propulsion. (arXiv:2201.00244v1 [physics.space-ph])

The application of directed energy to spacecraft mission design is explored using rapid transit to Mars as the design objective. An Earth-based laser array of unprecedented size (10~m diameter) and power (100~MW) is assumed to be enabled by ongoing developments in photonic laser technology. A phased-array laser of this size and incorporating atmospheric compensation would be able to deliver laser power to spacecraft in cislunar space, where the incident laser is focused into a hydrogen heating chamber via an inflatable reflector. The hydrogen propellant is then exhausted through a nozzle to realize specific impulses of 3000 s. The architecture is shown to be immediately reusable via a burn-back maneuver to return the propulsion unit while still within range of the Earth-based laser. The ability to tolerate much greater laser fluxes enables realizing the combination of high thrust and high specific impulse, making this approach favorable in comparison to laser-electric propulsion and

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03.01.2022
16:59 Phys.org Minimizing laser phase noise with machine learning

Ultra-precise lasers can be used for optical atomic clocks, quantum computers, power cable monitoring, and much more. But all lasers make noise, which researchers from DTU Fotonik want to minimize using machine learning.

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05:57 Arxiv.org Physics Realistic parameters of a continuous superradiant laser based on Sr-88. (arXiv:2112.15420v1 [physics.atom-ph])

The prospects of superradiant lasing on the 7.5 kHz wide $^1$S$_0$-$^3$P$_1$ transition in $^{88}$Sr is explored by using numerical simulations of two systems based on realistic experimental numbers [C. B. Silva et al, Towards a continuous superradiant laser on the strontium $^1$S$_0$-$^3$P$_0$ transition. Bulletin of the APS (2021)] [C.-C. Chen et al, Phys. Rev. Applied 12, 044014 (2019)]. One system uses the idea of demonstrating continuous superradiance in a simple, hot atom beam with high flux [H. Liu et al, Phys. Rev. Lett. 125, 253602 (2020)], and the other system is based on using ultra-cold atoms in a dipole guide. We find that the hot beam system achieves lasing above 3 $\cdot$ 10$^{12}$ atoms/s. It is capable of outputting hundreds of nW and suppressing cavity noise by a factor of 20-30. The second order Doppler shift causes a shift in the lasing frequency on the order of 500 Hz. For the cold atom beam we find that the output power is on the order of hundreds of pW, however

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30.12.2021
09:40 Arxiv.org Physics Group delay dispersion tuned femtosecond Kerr-lens mode-locked Ti:sapphire laser. (arXiv:2112.14516v1 [physics.optics])

We report on a new design for a femtosecond Ti:sapphire oscillator in which dispersion compensation is realized exclusively using mirrors, including special mirrors with third order dispersion. This makes the oscillator dynamically tunable over a spectral range of 45 nm using an intracavity wedge-pair; and it delivers 40 fs pulses at 80 MHz repetition rate. Due to the all-mirror design, the oscillator represents an attractive base for a tunable frequency comb for high precision spectroscopy applications.

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09:40 Arxiv.org Physics The role of tunneling in the ionization of atoms by ultrashort and intense laser pulses. (arXiv:2112.14336v1 [physics.atom-ph])

Using the improved soft-core potential of Majorosi et al, it is shown that classically allowed transport competes with quantum tunneling during the ionization of atoms by ultrashort and intense laser pulses. This is done by comparing exact probability densities with the ones obtained from purely classical propagation using the Truncated Wigner Approximation. Not only is classical transport capable of moving trajectories away from the core, but it can also furnish ionization probabilities of the same order as the quantum ones for intensities currently employed in experiments. Our results have implications ranging from a conceptual correction to the three-step model of higher-harmonics generation to the ongoing debate about tunneling time measurements in attoclocks.

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09:40 Arxiv.org Physics Design of AlGaAs Laser Power Converters for the First Transmission Window. (arXiv:2112.14110v1 [physics.app-ph])

Thermalization losses in Laser Power Converters for the first transmission window occur due to the energy difference between 808 nm wavelength photons and the GaAs bandgap energy which results in lower efficiency. In this work, we analyze the potential of increasing the bandgap using AlGaAs to minimize the energy difference. The optimum aluminum content is 7 % in both single and triple junction converters reaching a maximum ideal efficiency of 71% at 1 W/cm2 and 77% at 50 W/cm2.

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09:40 Arxiv.org Physics Quasi-probability Q for a single-atom laser generating in the 'semi-classical' regime. (arXiv:2112.13929v1 [quant-ph])

In the paper a model of a single-atom laser with incoherent pumping is theoretically investigated. In the stationary case, a linear homogeneous differential equation for the phase-averaged Hussimi Q-function is derived from the equation for the density operator of the system. In the regime when the coupling of the field with an atom is many times stronger than the coupling of the field with the reservoir providing its decay, an asymptotic solution of this equation is found. This solution makes it possible to describe some statistical features of a single-atom laser, in particular the weak sub-Poissonian photon statistics.

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09:40 Arxiv.org Physics Dynamics and stability conditions of semiconductor lasers under external optical feedback from both sides of the laser cavity. (arXiv:2112.13895v1 [physics.optics])

To increase the spectral efficiency of coherent communication systems, lasers with ever-narrower linewidths are required as they enable higher-order modulation formats with lower bit-error rates. In particular, semiconductor lasers are a key component due to their compactness, low power consumption, and potential for mass production. In field-testing scenarios their output is coupled to a fiber, making them susceptible to external optical feedback (EOF). This has a detrimental effect on its stability, thus it is traditionally countered by employing, for example, optical isolators and angled output waveguides. In this work, EOF is explored in a novel way with the aim to reduce and stabilize the laser linewidth. EOF has been traditionally studied in the case where it is applied to only one side of the laser cavity. In contrast, this work gives a generalization to the case of feedback on both sides. It is implemented using photonic components available via generic foundry platforms, thus

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28.12.2021
07:53 Arxiv.org Physics Optimized pulses for population transfer via laser induced continuum structures. (arXiv:2112.13768v1 [quant-ph])

We use optimal control in order to find the optimal shapes of pulses maximizing the population transfer between two bound states which are coupled via a continuum of states. We find that the optimal bounded controls acquire the bang-interior and interior-bang form, with the bang part corresponding to the maximum allowed control value and the interior part to values between zero and the maximum. Then, we use numerical optimal control to obtain the switching times and the interior control values. We compare our results with those obtained using Gaussian STIRAP pulses, and find that the optimal method performs better, with the extent of improvement depending on the effective two-photon detuning and the size of incoherent losses. When we consider effective two-photon resonance, the improvement is more dramatic for larger incoherent losses, while when we take into account the effective two-photon detuning, the improvement is better for smaller incoherent losses. We also obtain how the

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07:53 Arxiv.org Physics Electron trajectories and radiation growth rate in free electron laser with electromagnetic wiggler. (arXiv:2112.13313v1 [physics.plasm-ph])

An analysis of steady-state electron trajectories by simultaneous solution of the equation of motion and the dispersion relation (DR) for electromagnetic wave wiggler in free-electron laser (FEL) with axial magnetic field is presented. The effects of the normalized axial magnetic field and the normalized angular frequency of electromagnetic wave wiggler on axial and transverse velocity for group I and II orbits are investigated. A fluid model is used to obtain the DR for electrostatic wave and the right and the left circularly polarized electromagnetic waves with all relativistic effects included. This dispersion relation is solved numerically to investigation the unstable coupling among all waves. When the transverse velocity is small, only the FEL instability is found. In group II orbits, with large transverse velocity, new coupling between the negative and positive energy space charge waves as well as between the left circular wave and positive energy space charge wave are found.

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27.12.2021
21:53 Phys.org Transmissive-detected laser speckle imaging for blood flow monitoring in thick tissue

Blood flow velocity is an important parameter reflecting vascular function. Abnormal vascular function is closely related to the occurrence and development of many diseases, such as diabetes, arteriosclerosis, thrombosis and so on. Therefore, the monitoring of flow velocity is not only an important research target, but also an important clinical indicator.

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19:18 ScienceDaily.com Fingers made of laser light: Controlled grabbing and rotation of biological micro-objects

Scientists develop concept for feedback-controlled optical tweezers.These tweezers made of highly focused laser light can grab cell clusters in a controlled manner and rotate them in any direction. This will allow objects such as miniature tumors to be studied more specifically under the microscope.

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24.12.2021
11:29 Arxiv.org Physics Saturable absorption of free-electron laser radiation by graphite near the carbon K-edge. (arXiv:2112.12585v1 [physics.optics])

The interaction of intense light with matter gives rise to competing nonlinear responses that can dynamically change material properties. Prominent examples are saturable absorption (SA) and two-photon absorption (TPA), which dynamically increase and decrease the transmission of a sample depending on pulse intensity, respectively. The availability of intense soft X-ray pulses from free-electron lasers (FEL) has led to observations of SA and TPA in separate experiments, leaving open questions about the possible interplay between and relative strength of the two phenomena. Here, we systematically study both phenomena in one experiment by exposing graphite films to soft X-ray FEL pulses of varying intensity, with the FEL energy tuned to match carbon 1s to $\pi^*$ or 1s to $\sigma^*$ transitions. It is observed for lower intensities that the nonlinear contribution to the absorption is dominated by SA attributed to ground-state depletion; for larger intensities ($>10^{14}$ W/cm$^2$), TPA

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11:29 Arxiv.org Physics Low-divergence MeV-class proton beams from kHz-driven laser-solid interactions. (arXiv:2112.12581v1 [physics.acc-ph])

Proton beams with up to 100 pC bunch charge, 0.48 MeV cut-off energy and divergence as low as a $3^{\circ}$ were generated from solid targets at kHz repetition rate by a few-mJ femtosecond laser under controlled plasma conditions. The beam spatial profile was measured using a small aperture scanning time-of-flight detector. Detailed parametric studies were performed by varying the surface plasma scale length from 8 to 80 nm and the laser pulse duration from 4 fs to 1.5 ps. Numerical simulations are in good agreement with observations and, together with an in-depth theoretical analysis of the acceleration mechanism, indicate that high repetition rate femtosecond laser technology could be used to produce few-MeV protons beams for applications.

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11:29 Arxiv.org Physics Chirp-compensated pulsed titanium-sapphire laser system for precision spectroscopy. (arXiv:2112.12476v1 [physics.optics])

Active frequency-chirp compensation for a narrowband pulsed Titanium-Sapphire laser system is demonstrated using an intra-cavity electro-optic modulator resulting in improved spectral resolution and stability. With referencing to an optical frequency comb and further residual frequency chirp detection from shot-to-shot measurements, the resulting laser pulses are frequency up-converted for high-precision spectroscopy measurements in the VUV regime, where the relative uncertainty contribution due to frequency chirp is pushed to the $5 \times 10^{-11}$ level.

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23.12.2021
14:48 Nanowerk.com Fingers made of laser light: Controlled grabbing and rotation of biological micro-objects

Scientists develop concept for feedback-controlled optical tweezers. These tweezers made of highly focused laser light can grab cell clusters in a controlled manner and rotate them in any direction. This will allow objects such as miniature tumors to be studied more specifically under the microscope.

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07:04 Arxiv.org Physics Theoretical simulation and experimental verification of dynamic caustic manipulation using a deformable mirror for laser material processing. (arXiv:2112.11843v1 [physics.optics])

The influence of a deformable mirror on spatial light modulation in ultrafast lasers processing is demonstrated. The deformable mirror was integrated into an optical setup which contains an additional lens for generating a nearly linear focus shift in the focal plane behind the f-theta lens. The deformation of the mirror surface can be described by the Zernike terms Defocus, Astigmatism, and a combination of both, resulting in a cylindric lens behavior. The influence of the mirror surface deformation in this optical setup on the intensity distribution in the focal plane was simulated. From the simulation results, the caustic in the focal plane was calculated. The simulation results were compared to experiments using a picosecond laser with a maximum pulse energy of about 60 $\mu$J. We demonstrate that the initial astigmatism of the raw beam can be reduced using the deformable mirror. High linearity in the focus shift ($R^2 >98$%) and the generation of elliptical/ line intensity

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07:04 Arxiv.org Physics Charge and temporal characterisation of silicon sensors using a two-photon absorption laser. (arXiv:2112.11727v1 [physics.ins-det])

First measurements are presented from a newly commissioned two-photon absorption (TPA) setup at Nikhef. The characterisation of the various components of the system is discussed. Two planar silicon sensors, one being electron collecting and one hole collecting, are characterised with detailed measurements of the charge collection and time resolution. The TPA spot is determined to have a radius of 0.975(11) $\mu\text{m}$ and length of 23.8 $\mu\text{m}$ in silicon. The trigger time resolution of the system is shown to be maximally 30.4 ps. For both sensors, uniform charge collection is observed over the pixels, and the pixel side metallisation is imaged directly using the TPA technique. The best time resolution for a single pixel is found to be 600 ps and 560 ps for the electron and hole collecting sensors respectively, and is dominated by ASIC contributions. Further scans at different depths in the sensor and positions within the pixels have been performed and show a uniform response.

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22.12.2021
11:26 Arxiv.org CS Predicting Defects in Laser Powder Bed Fusion using in-situ Thermal Imaging Data and Machine Learning. (arXiv:2112.11212v1 [cs.LG])

Variation in the local thermal history during the laser powder bed fusion (LPBF) process in additive manufacturing (AM) can cause microporosity defects. in-situ sensing has been proposed to monitor the AM process to minimize defects, but the success requires establishing a quantitative relationship between the sensing data and the porosity, which is especially challenging for a large number of variables and computationally costly. In this work, we develop machine learning (ML) models that can use in-situ thermographic data to predict the microporosity of LPBF stainless steel materials. This work considers two identified key features from the thermal histories: the time above the apparent melting threshold (/tau) and the maximum radiance (T_{max}). These features are computed, stored for each voxel in the built material, are used as inputs. The binary state of each voxel, either defective or normal, is the output. Different ML models are trained and tested for the binary classification

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09:52 Arxiv.org Physics Analysis of the spontaneous emission limited linewidth of an integrated III-V/SiN laser. (arXiv:2112.11403v1 [physics.optics])

This paper describes a calculation of the spontaneous emission limited linewidth of a semiconductor laser consisting of hybrid or heterogeneously integrated, silicon and III-V intracavity components. Central to the approach are a) description of the multi-element laser cavity in terms of composite laser/free-space eigenmodes, b) use of multimode laser theory to treat mode competition and multiwave mixing, and c) incorporation of quantum-optical contributions to account for spontaneous emission effects. Application of the model is illustrated for the case of linewidth narrowing in an InAs quantum-dot laser coupled to a high-Q SiN cavity.

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09:52 Arxiv.org Physics Ab initio simulation of laser-induced electronic and vibrational coherence. (arXiv:2112.11083v1 [cond-mat.mtrl-sci])

We introduce an efficient quantum-semiclassical method based on time-dependent density-functional theory (TDDFT) for the parameter-free simulation of laser-induced electronic and vibrational coherences in condensed matter and their subsequent decay on the femtosecond timescale. With the example of (extended) carbon-conjugated molecules, we show that an ensemble-averaging approach with initial configurations taken from a nuclear quantum distribution remedies many of the shortcomings of the quantum-classical combination of real-time TDDFT and Ehrenfest molecular dynamics, naturally introducing a damping of electronic coherence and ultrafast non-adiabatic coupling between excited states. The number of required simulations decreases with the size and rigidity of the investigated compounds so that computational costs remain moderate even for large systems for which the mean-field approach shines. This work paves the way towards first-principles simulations of coherent nonlinear spectroscopy

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09:52 Arxiv.org Physics Exceptional Topological Surface Laser. (arXiv:2112.11017v1 [cond-mat.mes-hall])

Band topology has been studied as a design principle of realizing robust boundary modes. Here, by exploring non-Hermitian topology, we propose a three-dimensional topological laser that amplifies surface modes. The topological surface laser is protected by nontrivial topology around branchpoint singularities known as exceptional points. In contrast to two-dimensional topological lasers, the proposed three-dimensional setup can realize topological boundary modes without judicious gain at the edge or symmetry protection, which are thus robust against a broad range of disorders. We also propose a possible optical setup to experimentally realize the topological surface laser. Our results provide a general guiding principle to construct non-Hermitian topological devices in three-dimensional systems.

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21.12.2021
19:49 ScienceDaily.com IT security: Computer attacks with laser light

Computer systems that are physically isolated from the outside world (air-gapped) can still be attacked. This is demonstrated by IT security experts. They show that data can be transmitted to light-emitting diodes of regular office devices using a directed laser. With this, attackers can secretly communicate with air-gapped computer systems over distances of several meters. In addition to conventional information and communication technology security, critical IT systems need to be protected optically as well.

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15:26 Zdnet.com Glowforge Pro review: Laser cutting and engraving for serious hobbyists and makers

It's not cheap, but if you have the space and can put up with some noise and odour, the Glowforge Pro will allow you to undertake an impressive range of creative projects.

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07:03 Arxiv.org CS Supervised laser-speckle image sampling of skin tissue to detect very early stage of diabetes by its effects on skin subcellular properties. (arXiv:2112.10024v1 [eess.IV])

This paper investigates the effectiveness of an expert system based on K-nearest neighbors algorithm for laser speckle image sampling applied to the early detection of diabetes. With the latest developments in artificial intelligent guided laser speckle imaging technologies, it may be possible to optimise laser parameters, such as wavelength, energy level and image texture measures in association with a suitable AI technique to interact effectively with the subcellular properties of a skin tissue to detect early signs of diabetes. The new approach is potentially more effective than the classical skin glucose level observation because of its optimised combination of laser physics and AI techniques, and additionally, it allows non-expert individuals to perform more frequent skin tissue tests for an early detection of diabetes.

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05:31 Arxiv.org Physics Absolute keV X-ray yield and conversion efficiency in over dense Si petawatt laser plasma. (arXiv:2112.10757v1 [physics.plasm-ph])

Laser-produced plasmas are bright, short sources of X-rays often used for time-resolved imaging and spectroscopy. Absolute measurement requires accurate knowledge of laser-to-x-ray conversion efficiencies, spectrum, photon yield and angular distribution. Here we report on soft X-ray emission from a thin Si foil irradiated by a sub-PW picosecond laser pulse. These absolute measurements cover a continuous and broad spectral range that extends from 4.75 to 7.5 Angstroms (1.7-2.6 keV). The X-ray spectrum consists of spectral line transitions from highly charged ions and broadband emission with contributions from recombination, and free-free processes that occur as electrons decelerate in plasma electromagnetic fields. These quantitative measurements are compared to particle-in-cell simulations allowing us to distinguish bremsstrahlung and synchrotron contributions to the free-free emission. We found that experiment and simulation estimations of laser-to-bremsstrahlung conversion efficiency

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05:31 Arxiv.org Physics Laser Cooling Scheme for the Carbon Dimer ($^{12}$C$_2$). (arXiv:2112.10745v1 [physics.atom-ph])

We report on a scheme for laser cooling of $^{12}$C$_2$. We have calculated the branching ratios for cycling and repumping transitions and calculated the number of photon scatterings required to achieve deflection and laser cooling of a beam of $C_2$ molecules under realistic experimental conditions. Our results demonstrate that C$_2$ cooling using the Swan ($d^3\Pi_\text{g} \leftrightarrow a^3\Pi_\text{u}$) and Duck ($d^3\Pi_\text{g} \leftrightarrow c^3\Sigma_\text{u}^+$) bands is achievable via techniques similar to state-of-the-art molecular cooling experiments. The Phillips ($A^1\Pi_\text{u} \leftrightarrow X^1\Sigma_\text{g}^+$) and Ballik-Ramsay ($b^3\Sigma_\text{g}^- \leftrightarrow a^3\Pi_\text{u}$) bands offer the potential for narrow-line cooling. This work opens up a path to cooling of molecules with carbon-carbon bonds and may pave the way toward quantum control of organic molecules.

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05:31 Arxiv.org Physics Enhancing fiber atom interferometer by in-fiber laser cooling. (arXiv:2112.10088v1 [physics.atom-ph])

We demonstrate an inertia sensitive atom interferometer optically guided inside a 22-cm-long negative curvature hollow-core photonic crystal fiber with an interferometer time of 20 ms. The result prolongs the previous fiber guided atom interferometer time by three orders of magnitude. The improvement arises from the realization of in-fiber {\Lambda}-enhanced gray molasses and delta-kick cooling to cool atoms from 32 {\mu}K to below 1 {\mu}K in 4 ms. The in-fiber cooling overcomes the inevitable heating during the atom loading process and allows a shallow guiding optical potential to minimize decoherence. Our results permit bringing atoms close to source fields for sensing and could lead to compact inertial quantum sensors with a sub-millimeter resolution.

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05:31 Arxiv.org Physics Supervised laser-speckle image sampling of skin tissue to detect very early stage of diabetes by its effects on skin subcellular properties. (arXiv:2112.10024v1 [eess.IV])

This paper investigates the effectiveness of an expert system based on K-nearest neighbors algorithm for laser speckle image sampling applied to the early detection of diabetes. With the latest developments in artificial intelligent guided laser speckle imaging technologies, it may be possible to optimise laser parameters, such as wavelength, energy level and image texture measures in association with a suitable AI technique to interact effectively with the subcellular properties of a skin tissue to detect early signs of diabetes. The new approach is potentially more effective than the classical skin glucose level observation because of its optimised combination of laser physics and AI techniques, and additionally, it allows non-expert individuals to perform more frequent skin tissue tests for an early detection of diabetes.

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20.12.2021
19:34 WhatReallyHappened.com Sea Glows Red as Navy Fires New Laser Weapon in the Middle East

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09:39 Arxiv.org CS Two-level Method Part-scale Thermal Analysis of Laser Powder Bed Fusion Additive Manufacturing. (arXiv:2112.09461v1 [math.NA])

Numerical simulations of a complete laser powder bed fusion (LPBF) additive manufacturing (AM) process are extremely challenging or even impossible to achieve without a radical model reduction of the complex physical phenomena occurring during the process. However, even when we adopt reduced model with simplified physics, the complex geometries of parts usually produced by LPBF AM processes make this kind of analysis computationally expensive. In fact, small geometrical features - which might be generated when the part is design following the principal of the so-called design for AM, for instance, by means of topology optimization procedures - often require complex conformal meshes. Immersed boundary methods seem to offer a valid alternative to deal with this kind of complexity. The two-level method lies within this family of numerical methods and presents a very flexible tool to deal with multi-scale problems. In this contribution, we apply the recently introduced two-level method to

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08:06 Arxiv.org Math Two-level Method Part-scale Thermal Analysis of Laser Powder Bed Fusion Additive Manufacturing. (arXiv:2112.09461v1 [math.NA])

Numerical simulations of a complete laser powder bed fusion (LPBF) additive manufacturing (AM) process are extremely challenging or even impossible to achieve without a radical model reduction of the complex physical phenomena occurring during the process. However, even when we adopt reduced model with simplified physics, the complex geometries of parts usually produced by LPBF AM processes make this kind of analysis computationally expensive. In fact, small geometrical features - which might be generated when the part is design following the principal of the so-called design for AM, for instance, by means of topology optimization procedures - often require complex conformal meshes. Immersed boundary methods seem to offer a valid alternative to deal with this kind of complexity. The two-level method lies within this family of numerical methods and presents a very flexible tool to deal with multi-scale problems. In this contribution, we apply the recently introduced two-level method to

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08:06 Arxiv.org Physics Laser stimulation of muscle activity with simultaneous detection using a diamond colour centre biosensor. (arXiv:2112.09516v1 [physics.bio-ph])

The detection of physiological activity at the microscopic level is key for understanding the function of biosystems and relating this to physical structure. Current sensing methods often rely on invasive probes to stimulate and detect activity, bearing the risk of inducing damage in the target system. In recent years, a new type of biosensor based on color centers in diamond offers the possibility to passively, noninvasively sense and image living biological systems. Here, we use such a sensor for the \textit{in-vitro} recording of the local magnetic field generated by tightly focused, high intensity pulsed laser optogenetic neuromuscular stimulation of the extensor digitorum longus muscles. Recordings captured a compound action potential response and a slow signal component which we seek to explain using a detailed model of the biological system. We show that our sensor is capable of recording localized neuromuscular activity from the laser stimulation site without photovoltaic or

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08:06 Arxiv.org Physics Nanoscale laser flash measurements of diffuson transport in amorphous Ge and Si. (arXiv:2112.09289v1 [physics.app-ph])

Thermal properties of amorphous materials have attracted significant attention due to their technological importance in electronic devices. Additionally, the disorder induced breakdown of the phonon gas model makes vibrational transport in amorphous materials a topic of fundamental interest. In the past few decades, theoretical concepts such as propagons, diffusons, and locons have emerged to describe different types of vibrational modes in disordered solids. But experiments can struggle to accurately determine which types of vibrational states carry the majority of the heat. In the present study, we describe a new experimental method for characterizing vibrational transport in nanoscale amorphous layers. We use nanoscale laser flash measurements (front/back time-domain thermoreflectance) to investigate thermal transport mechanisms in amorphous Ge and amorphous Si thin-films. We observe a nearly linear relationship between the amorphous film's thermal resistance and the film's

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08:06 Arxiv.org Physics 36 Hz integral linewidth laser based on a photonic integrated 4.0-meter coil resonator. (arXiv:2112.09246v1 [physics.optics])

Laser stabilization sits at the heart of many precision scientific experiments and applications, including quantum information science, metrology and atomic timekeeping. These systems narrow the laser linewidth and stabilize the carrier by use of Pound-Drever-Hall (PDH) locking to a table-scale, ultra-high quality factor (Q), vacuum spaced Fabry-Perot reference cavity. Integrating these cavities, to bring characteristics of PDH stabilization to the chip-scale, is critical to reduce their size, cost, and weight, and enable a wide range of portable and system-on-chip applications. We report a significant advance in integrated laser linewidth narrowing, stabilization and noise reduction, by use of a photonic integrated 4.0-meter-long coil resonator to stabilize a semiconductor laser. We achieve a 36 Hz 1/{\pi}-integral linewidth, an Allan deviation (ADEV) of 1.8x10^{-13} at 10 ms measurement time, and a 2.3 kHz/sec drift, to the best of our knowledge the lowest integral linewidth and

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17.12.2021
10:14 Arxiv.org CS Computational metrics and parameters of an injection-locked large area semiconductor laser for neural network computing. (arXiv:2112.08947v1 [cs.ET])

Artificial neural networks have become a staple computing technique in many fields. Yet, they present fundamental differences with classical computing hardware in the way they process information. Photonic implementations of neural network architectures potentially offer fundamental advantages over their electronic counterparts in terms of speed, processing parallelism, scalability and energy efficiency. Scalable and high performance photonic neural networks (PNNs) have been demonstrated, yet they remain scarce. In this work, we study the performance of such a scalable, fully parallel and autonomous PNN based on a large area vertical-cavity surface-emitting laser (LA-VCSEL). We show how the performance varies with different physical parameters, namely, injection wavelength, injection power, and bias current. Furthermore, we link these physical parameters to the general computational measures of consistency and dimensionality. We present a general method of gauging dimensionality in

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09:13 Arxiv.org Physics Role of focusing distance in picosecond laser-induced Cu plasma spectra. (arXiv:2112.08942v1 [physics.plasm-ph])

To study the effects of focusing distance on the characteristics of copper plasma, a picosecond laser was utilized to ablate a pure copper plate to generate a plasma spectrum. Following numerous experiments on the subject, three significant factors have been determined: lens focal length, pulse energy and the lens-to-sample distance. These factors were employed to analyze the spectral intensity, plasma temperature and electron density in the local thermodynamic equilibrium (LTE) and optically thin condition. Due to the shielding effects of mixed plasma, the strongest spectral intensity can be obtained in the pre-focused case rather than on the focus, no matter how much beam irradiance was employed. The more intensive the beam irradiance is, the more the optimal position is distant from the focal point. Similarly, the evolution of plasma temperature and electron density was shown a peak in the pre-focused case, which is consistent with the trend of spectral intensity. For the case of

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09:13 Arxiv.org Physics Two-color grating magneto-optical trap for narrow-line laser cooling. (arXiv:2112.08833v1 [physics.atom-ph])

We demonstrate for the first time the two-color cooling and trapping of alkaline-earth atoms in a grating magneto-optical trap (gMOT). The trap is formed by a single incident laser beam together with four secondary beams that are generated via diffraction from a nanostructured wafer. A grating structure for a gMOT operating with strontium atoms is optimized and fabricated. We trap $10^6$ $^{88}$Sr atoms on the $^1$S$_0$ $\rightarrow$ $^1$P$_1$ transition at $461\;\mathrm{nm}$ and transfer $25\;\%$ of these atoms to the second cooling stage on the narrower $^1$S$_0$ $\rightarrow$ $^3$P$_1$ intercombination transition at $689\;\mathrm{nm}$, preparing a sample of $2.5\times 10^5$ atoms at $5\;\mu$K. These results demonstrate for the first time the applicability of the gMOT technology in conjunction with two widely differing wavelengths and enable the continued miniaturization of alkaline-earth based quantum technologies like optical atomic clocks.

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09:13 Arxiv.org Physics Thermal Model for Time-Domain Thermoreflectance Experiments in a Laser Flash Geometry. (arXiv:2112.08734v1 [physics.app-ph])

Time domain thermoreflectance (TDTR) is a well established pump/probe method for measuring thermal conductivity and interface conductance of multilayers.Interpreting signals in a TDTR experiment requires a thermal model. We present a frequency-domain solution to the heat-diffusion equation of a multilayer in response to nonhomogenous laser heating. The model allows analysis of experiments where pump and probe beams irradiate opposite sides of a multilayer. We call such a geometry a front/back experiment to differentiate such experiments from standard TDTR experiments. In standard front/front TDTR experiments, both pump and probe beams irradiate the surface of a multilayer. As an example, we consider amorphous Ge. We consider how signals differ in a front/front vs. front/back geometry and compare model predictions to experimental data.

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09:13 Arxiv.org Physics Retinal blood flow imaging with combined full-field swept-source optical coherence tomography and laser Doppler holography. (arXiv:2112.08494v1 [physics.med-ph])

Full-field swept-source optical coherence tomography (FF-SS-OCT) and laser Doppler holography (LDH) are two holographic imaging techniques presenting unique capabilities for ophthalmology. We report on interlaced FF-SS-OCT and LDH imaging with a single instrument. Effectively, retinal blood flow and pulsation could be quasi-simultaneously monitored. This instrument holds potential for a wide scope of ophthalmic applications.

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16.12.2021
20:54 WhatReallyHappened.com US Navy Warship Fires Laser To Destroy Floating Target In Gulf Of Aden Where Iran-Backed Houthi Rebels Have Used Bomb-Laden Drone Boats To Attack Ships

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11:54 Arxiv.org Physics Towards a direct measurement of the quantum vacuum Lagrangian coupling coefficients using two counter propagating super-intense laser pulses. (arXiv:2112.08302v1 [physics.optics])

In this paper we will show that photon-photon collision experiments using extreme lasers can provide measurable effects giving fundamental information about the essence of QED, its Lagrangian. A possible scenario with two counterpropagating ultraintense lasers for an experiment to detect scattering between optical photons is analyzed. We discuss the importance of the pulse widths and waists, the best scenario for overlapping the beams and signal detection, as well as ways to distinguish the signal from the noise. This would need a high-precision measurement, with control of temporal jitter and noise. We conclude that such experiment is barely feasible at 10^{23} W/cm^2 and very promising at 10^{24} W/cm^2

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11:54 Arxiv.org Physics An Innovative Transverse Emittance Cooling Technique using a Laser-Plasma Wiggler. (arXiv:2112.08163v1 [physics.acc-ph])

We propose an innovative beam cooling scheme based on laser driven plasma wakefields to address the challenge of high luminosity generation for a future linear collider. For linear colliders, beam cooling is realised by means of damping rings equipped with wiggler magnets and accelerating cavities. This scheme ensures systematic reduction of phase space volume through synchrotron radiation emission whilst compensating for longitudinal momentum loss via an accelerating cavity. In this paper, the concept of a plasma wiggler and its effective model analogous to a magnetic wiggler are introduced; relation of plasma wiggler characteristics with damping properties are demonstrated; underpinning particle-in-cell simulations for laser propagation optimisation are presented. The oscillation of transverse wakefields and resulting sinusoidal probe beam trajectory are numerically demonstrated. The formation of an order of magnitude larger effective wiggler field compared to conventional wigglers

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11:54 Arxiv.org Physics A simple approach of broadband mid-infrared pulse generation with a mode-locked Yb-doped fiber laser. (arXiv:2112.08076v1 [physics.optics])

Broadband mid-infrared (MIR) molecular spectroscopy demands a bright and broadband light source in the molecular fingerprint region. To this end, intra-pulse difference frequency generation (IDFG) has shown excellent properties among various techniques. However, previous IDFG systems have mainly used unconventional long-wavelength 2-${\mu}$m ultrashort pulsed lasers. A few systems have been demonstrated with 1-${\mu}$m lasers, but they use bulky 100-W-class high-power Yb thin-disk lasers. In this work, we demonstrate a simple and robust approach of 1-${\mu}$m-pumped broadband IDFG with a conventional mode-locked Yb-doped fiber laser. We first generate 3.3-W, 12.1-fs ultrashort pulses at 50 MHz by a simple combination of spectral broadening with a short single-mode fiber and pulse compression with chirped mirrors. Then, we use them for pumping a thin orientation-patterned gallium phosphide (OP-GaP) crystal, generating 1.2-mW broadband MIR pulses with the -20-dB bandwidth of 480

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11:54 Arxiv.org Physics Laser-lithographically written micron-wide superconducting nanowire single-photon detectors. (arXiv:2112.07976v1 [physics.ins-det])

We demonstrate the fabrication of micron-wide tungsten silicide superconducting nanowire single-photon detectors on a silicon substrate using laser lithography. We show saturated internal detection efficiencies with wire widths from 0.59$\mu$m to 1.43$\mu$m under illumination at 1550nm. We demonstrate both straight wires, as well as meandered structures. Single-photon sensitivity is shown in devices up to 4mm in length. Laser-lithographically written devices allow for fast and easy structuring of large areas while maintaining a saturated internal efficiency for wire width around 1$\mu$m.

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11:54 Arxiv.org Physics SPring-8 LEPS2 beamline: A facility to produce a multi-GeV photon beam via laser Compton scattering. (arXiv:2112.07832v1 [physics.acc-ph])

We have constructed a new laser-Compton-scattering facility, called the LEPS2 beamline, at the 8-GeV electron storage ring, SPring-8. This facility provides a linearly polarized photon beam in a tagged energy range of 1.3--2.4 GeV. Thanks to a small divergence of the low-emittance storage-ring electrons, the tagged photon beam has a size (sigma) suppressed to about 4 mm even after it travels about 130 m to the experimental building that is independent of the storage ring building and contains large detector systems. This beamline is designed to achieve a photon beam intensity higher than that of the first laser-Compton-scattering beamline at SPring-8 by adopting the simultaneous injection of up to four high-power laser beams and increasing a transmittance for the long photon-beam path up to about 77%. The new beamline is under operation for hadron photoproduction experiments.

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05:27 AntiWar.com US Navy Tests New Laser Weapon Off Yemen Coast

The laser destroyed a floating target The post US Navy Tests New Laser Weapon Off Yemen Coast appeared first on News From Antiwar.com.

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15.12.2021
20:52 RT.com US Navy tests laser weapon in Middle East

The US Navy has used a high-energy laser weapon to destroy a floating target in the Gulf of Aden. The test took place in a war-ravaged waterway known for its strategic importance. Read Full Article at RT.com

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07:35 Arxiv.org Physics Dense Polarized Positrons from Laser-Irradiated Foil Targets in the QED Regime. (arXiv:2112.07451v1 [physics.plasm-ph])

Dense positrons are shown to be effectively generated from laser-solid interactions in the strong-field quantum electrodynamics (QED) regime. Whether these positrons are polarized has not yet been reported, limiting their potential applications. Here, by QED particle-in-cell simulations including electron-positron spin and photon polarization effects, we investigate a typical laser-solid setup that an ultraintense linearly polarized laser irradiates a foil target with $\mu$m-scale-length preplasma. We find that once the positron yield becomes appreciable with the laser intensity exceeding $10^{24}~\rm W/\rm cm^2$, the positrons are obviously polarized. The polarized positrons can acquire $>30\%$ polarization degree and $>30$ nC charge with a flux of $10^{12}\,{\rm sr}^{-1}$. The polarization relies on the deflected angles and can reach 60\% at some angles and energies. The angularly-dependent polarization is attributed to the asymmetrical laser fields positrons undergo in the skin

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07:35 Arxiv.org Physics Laser-induced periodic surface structured electrodes with a 45 % energy saving in electrochemical fuel generation through field localization. (arXiv:2112.07044v1 [physics.chem-ph])

Electrochemical oxidation-reduction of radicals is a green and environmentally friendly approach to generating fuels. These reactions, however, suffer from sluggish kinetics due to a low local concentration of radicals around the electrocatalyst. A large electrode potential can enhance the fuel generation efficiency via enhancing the radical concentration around the electrocatalyst sites, but this comes at the cost of electricity. Here, we report about a 45 percent saving in energy to achieve an electrochemical hydrogen generation rate of 10 mA per cm2 through localized electric field-induced enhancement in the reagent concentration (LEFIRC) at laser-induced periodic surface structured (LIPSS) electrodes. The finite element model is used to simulate the spatial distribution of the electric field to understand the effects of LIPSS geometric parameters in field localization. When the LIPSS patterned electrodes are used as substrates to support Pt-C and RuO2 electrocatalysts, the

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14.12.2021
10:15 Arxiv.org Physics Effect of homogenization on precipitation behavior and strengthening of 17-4PH stainless steel fabricated using laser powder bed fusion. (arXiv:2112.06289v1 [cond-mat.mtrl-sci])

Effective post-heat treatment is critical to achieve desired microstructure for high-performance in additively manufactured (AM) components. In this work, the influence of homogenization on microstructure-property relationship in 17-4PH steels has been investigated. Precipitation of NbC, oxides, and {\epsilon}-Cu were observed in the as-built 17-4PH steels. To design an optimum post-heat treatment, homogenization was performed at 1050oC for different times followed by aging at 482oC for 1 hour. It was identified that homogenization for 1 hour followed by aging leads to the best combination of strength and ductility due to the refinement of martensite and prior austenite grains. Improved tensile properties were achieved for the post-heat-treated alloys that exceeded the traditionally fabricated 17-4PH steels. Through comprehensive microstructure characterization, it was deduced that the incoherent {\epsilon}-Cu precipitates in the as-built alloy were dissolved through homogenization,

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10:15 Arxiv.org Physics Laser array of coherent beam combination system revisited: angular domain perspective and fractal-based optimization. (arXiv:2112.06012v1 [physics.optics])

Coherent beam combination (CBC) of fiber lasers holds promise for achieving high brightness laser systems, which have given rise to widespread applications such as particle accelerator, space debris removal, and industrial fabrication. The emitting laser array of CBC systems offers intriguing features in terms of agile beam steering, flexible beam shaping, and high scalability for output power and array elements. However, the theoretical model of the laser array in CBC systems is less well explored beyond the routine angular-spectrum method, where methods for optimizing the laser array configuration are more limited. Here, we explore the theory for the laser array of CBC systems in the view of angular domain. The laser array is represented by the composition of angular harmonics, the orthogonal basis over the azimuthal plane, and we elucidate the formation of mainlobe and sidelobes of the far-field interference pattern by using the orbital angular momentum spectrum analysis and

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11.12.2021
15:57 RT.com Turkey makes drone that can destroy bombs with laser beam

Turkey creates drone that can destroy bombs with its laser beam Turkey builds bomb-destroying drone Tukey has developed a bomb disposal drone equipped with a laser beam that can burn through carbon steel. Read Full Article at RT.com

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10.12.2021
18:25 ScienceDaily.com Atom laser creates reflective patterns similar to light

Cooled to almost absolute zero, atoms not only move in waves like light but also can be focused into shapes called caustics, similar to the reflecting or refracting patterns light makes on the bottom of a swimming pool or through a curved wine glass. In experiments, scientists have developed a technique to see these matter wave caustics by placing attractive or repulsive obstacles in the path of a cold atom laser. The results are curving cusps or folds, upward or downward 'V' shapes. These caustics have potential applications for highly precise measurement or timing devices such as interferometers and atomic clocks.

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13:05 Phys.org Atom laser creates reflective patterns similar to light

Cooled to almost absolute zero, atoms not only move in waves like light but also can be focused into shapes called caustics, similar to the reflecting or refracting patterns light makes on the bottom of a swimming pool or through a curved wine glass.

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07:03 Arxiv.org Physics Biomimetic Hierarchical Structuring of PLA by Ultra-Short Laser Pulses for Processing of Tissue Engineered Matrices: Study of Cellular and Antibacterial Behavior. (arXiv:2112.05026v1 [physics.bio-ph])

The influence of ultra-short laser modification on the surface morphology and possible chemical alteration of poly-lactic acid (PLA) matrix in respect to the optimization of cellular and antibacterial behavior were investigated in this study. Scanning electron microscopy (SEM) morphological examination of the processed PLA surface showed the formation of diverse hierarchical surface microstructures, generated by irradiation with a range of laser fluences (F) and scanning velocities (V) values. By controlling the laser parameters, diverse surface roughness can be achieved, thus influencing cellular dynamics. This surface feedback can be applied to finely tune and control diverse biomaterial surface properties like wettability, reflectivity, and biomimetics. The triggering of thermal effects, leading to the ejection of material with subsequent solidification and formation of raised rims and 3D-like hollow structures along the processed zones, demonstrated a direct correlation to the

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