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13.11.2019
19:57 LiveScience.comNew, 'Hidden' State of Matter Coaxed into Being by Ultrafast Laser Flashes

Physicists think this might be the first of many hidden states of matter that could be uncovered using laser flashes.

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19:52 ScienceDaily.comLaser: Multi-millijoule 3-cycle pulses at 318 W generated

A team has generated multi-millijoule 3-cycle pulses at 318 W average power level. These results mark a significant milestone in few-cycle laser technology paving the way towards industrial applications.

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14:57 Phys.orgA milestone in ultrashort-pulse laser oscillators

With the demonstration of a sub-picosecond thin-disk laser oscillator delivering a record-high 350-watt average output power, physicists at ETH Zurich set a new benchmark and pave the path toward even more powerful lasers.

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12:41 Phys.orgIEA says world needs 'laser-like focus' to bring down emissions

The world must do much more to slash emissions if it is to defuse the climate change time bomb and deliver sustainable energy for a growing population, the International Energy Agency said Wednesday.

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11:35 Arxiv.org PhysicsAbsolute measurement of laser ionization yield in atmospheric pressure range gases over 14 decades. (arXiv:1911.04990v1 [physics.plasm-ph])

Strong-field ionization is central to intense laser-matter interactions. However, standard ionization measurements have been limited to extremely low density gas samples, ignoring potential high density effects. Here, we measure strong-field ionization in atmospheric pressure range air, N2 and Ar over 14 decades of absolute yield, using mid-IR picosecond avalanche multiplication of single electrons. Our results are consistent with theoretical rates for isolated atoms and molecules and quantify the ubiquitous presence of ultra-low concentration gas contaminants that can significantly affect laser-gas interactions.

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12.11.2019
23:07 ScienceDaily.comA milestone in ultrashort-pulse laser oscillators

With the demonstration of a sub-picosecond thin-disk laser oscillator delivering a record-high 350-W average output power, physicists set a new benchmark and pave the path towards even more powerful lasers.

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12:03 Phys.orgPhysics experiment with ultrafast laser pulses produces a previously unseen phase of matter

Adding energy to any material, such as by heating it, almost always makes its structure less orderly. Ice, for example, with its crystalline structure, melts to become liquid water, with no order at all.

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06:51 Arxiv.org PhysicsSemiclassical analysis of photoelectron interference in a synthesized two-color laser pulse. (arXiv:1911.04035v1 [physics.atom-ph])

We measure the photoelectron energy spectra from strong-field ionization of Kr in a two-color laser pulse consisting of a strong 400-nm field and a weak 800-nm field. The intensities of the main above-threshold ionization (ATI) and sideband peaks in the photoelectron energy spectra oscillate roughly oppositely with respect to the relative phase between the two-color components. We study the photoelectron interferometry in strong-field ATI regime from the view of interference of different electron trajectories in order to extend RABBITT type analysis to the strong-field regime. Based on the strong-field approximation model, we obtain analytical expressions for the oscillations of both ATI and sideband peaks with the relative phase. A phase shift of \pi/4 with respect to the field maximum of the two-color laser pulse is revealed for the interference maximum in the main ATI peak without

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06:51 Arxiv.org PhysicsFemtosecond laser produced periodic plasma in a colloidal crystal probed by XFEL radiation. (arXiv:1911.03752v1 [cond-mat.soft])

With the rapid development of short-pulse intense laser sources, studies of matter under extreme irradiation conditions enter further unexplored regimes. In addition, an application of X-ray Free- Electron Lasers (XFELs), delivering intense femtosecond X-ray pulses allows to investigate sample evolution in IR pump - X-ray probe experiments with an unprecedented time resolution. Here we present the detailed study of periodic plasma created from the colloidal crystal. Both experimental data and theory modeling show that the periodicity in the sample survives to a large extent the extreme excitation and shock wave propagation inside the colloidal crystal. This feature enables probing the excited crystal, using the powerful Bragg peak analysis, in contrast to the conventional studies of dense plasma created from bulk samples for which probing with Bragg diffraction technique is not possible.

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06:51 Arxiv.org PhysicsPulsed laser deposition of single phase n- and p-type Cu2O thin films with low resistivity. (arXiv:1911.03727v1 [cond-mat.mtrl-sci])

Low resistivity (~3-24 mOhm.cm) with tunable n- and p-type phase pure Cu2O thin films have been grown by pulsed laser deposition at 25-200 0C by varying the background oxygen partial pressure (O2pp). Capacitance data obtained by electrochemical impedance spectroscopy was used to determine the conductivity (n- or p-type), carrier density, and flat band potentials for samples grown on indium tin oxide (ITO) at 25 0C. The Hall mobility of the n- and p-type Cu2O was estimated to be ~ 0.85 cm2.V-1s-1 and ~ 4.78 cm2.V-1s-1 respectively for samples grown on quartz substrate at 25 0C. An elevated substrate temperature ~ 200 0C with O2pp = 2 - 3 mTorr yielded p-type Cu2O films with six orders of magnitude higher resistivities in the range ~ 9 - 49 kOhm.cm and mobilities in the range ~ 13.5 - 22.2 cm2.V-1s-1. UV-Vis-NIR diffuse reflectance spectroscopy showed optical bandgaps of Cu2O films in the range

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11.11.2019
09:46 Arxiv.org PhysicsNonlinear dynamics of laser-generated ion-plasma gratings: a unified description. (arXiv:1911.03440v1 [physics.plasm-ph])

Laser-generated plasma gratings are dynamic optical elements for the manipulation of coherent light at high intensities, beyond the damage threshold of solid-stated based materials. Their formation, evolution and final collapse require a detailed understanding. In this paper, we present a model to explain the nonlinear dynamics of high amplitude plasma gratings in the spatially periodic ponderomotive potential generated by two identical counter-propagating lasers. Both, fluid and kinetic aspects of the grating dynamics are analyzed. It is shown that the adiabatic electron compression plays a crucial role as the electron pressure may reflect the ions from the grating and induce the grating to break in an X-type manner. A single parameter is found to determine the behaviour of the grating and distinguish three fundamentally different regimes for the ion dynamics: completely reflecting,

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09:46 Arxiv.org PhysicsTracking with wakefields in dielectric laser acceleration grating structures. (arXiv:1911.03337v1 [physics.acc-ph])

Due to the tiny apertures of dielectric laser acceleration grating structures within the range of the optical wavelength, wakefields limit the bunch charge for relativistic electrons to a few femtocoulomb. In this paper, we present a wakefield upgrade of our six-dimensional tracking scheme DLAtrack6D in order to analyze these limitations. Simulations with CST Studio Suite provide the wake functions to calculate the kicks within each tracking step. Scaling laws and the dependency of the wake on geometrical changes are calculated. The tracking with wakefields is applied to beam and structure parameters following recently performed and planned experiments. We compare the results to analytical models and identify intensity limits due to the transverse beam breakup and strong head-tail instability. Furthermore, we reconstruct phase advance spectrograms and use them to analyze possible

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09:46 Arxiv.org PhysicsAdditive manufactured isotropic NdFeB magnets by stereolithography, fused filament fabrication, and selective laser sintering. (arXiv:1911.02881v1 [physics.app-ph])

Magnetic isotropic NdFeB powder is processed by the following additive manufacturing methods: (i) stereolithography (SLA), (ii) fused filament fabrication (FFF), and (iii) selective laser sintering (SLS). For the first time, a stereolithography based method is used to 3D print hard magnetic materials. FFF and SLA use a polymer matrix material as binder, SLS sinters the powder directly. All methods use the same hard magnetic NdFeB powder material. Complex magnets with small feature sizes in a superior surface quality can be printed with SLA. The magnetic properties for the processed samples are investigated and compared. SLA can print magnets with a remanence of 388 mT and a coercivity of 0.923 T. A complex magnetic design for speed wheel sensing applications is presented and printed with all methods.

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09:46 Arxiv.org CSMapless Navigation among Dynamics with Social-safety-awareness: a reinforcement learning approach from 2D laser scans. (arXiv:1911.03074v1 [cs.RO])

We propose a method to tackle the problem of mapless collision-avoidance navigation where humans are present using 2D laser scans. Our proposed method uses ego-safety to measure collision from the robot's perspective while social-safety to measure the impact of our robot's actions on surrounding pedestrians. Specifically, the social-safety part predicts the intrusion impact of our robot's action into the interaction area with surrounding humans. We train the policy using reinforcement learning on a simple simulator and directly evaluate the learned policy in Gazebo and real robot tests. Experiments show the learned policy can be smoothly transferred without any fine tuning. We observe that our method demonstrates time-efficient path planning behavior with high success rate in mapless navigation tasks. Furthermore, we test our method in a navigation among dynamic crowds task considering both

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09.11.2019
15:19 WhatReallyHappened.comHACKERS CAN SILENTLY CONTROL YOUR GOOGLE HOME, ALEXA, SIRI WITH LASER LIGHT

SOURCE: THE HACKER NEWS A team of cybersecurity researchers has discovered a clever technique to remotely inject inaudible and invisible commands into voice-controlled devices — all just by shining a laser at the targeted device instead of using spoken words.
Dubbed 'Light Commands,' the hack relies on a vulnerability in MEMS microphones embedded in widely-used popular voice-controllable systems that unintentionally respond to light as if it were sound.
According to experiments done by a team of researchers from Japanese and Michigan Universities, a remote attacker standing at a distance of several meters away from a device can covertly trigger the attack by simply modulating the amplitude of laser light to produce an acoustic pressure wave.
"By modulating an electrical signal in the intensity of a light beam, attackers can trick microphones into producing electrical signals as if

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08.11.2019
15:17 Financial TimesJoshua Wong: ‘We used to play laser tag. Now we face bullets’

The face of the Hong Kong protest movement on defying Beijing

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07.11.2019
04:57 Arxiv.org PhysicsModel-independent inference of laser intensity. (arXiv:1911.02349v1 [physics.plasm-ph])

An ultrarelativistic electron beam passing through an intense laser pulse emits radiation around its direction of propagation into a characteristic angular profile. Here we show that measurement of the variances of this profile in the planes parallel and perpendicular to the laser polarization, and the mean initial and final energies of the electron beam, allows the intensity of the laser pulse to be inferred in way that is independent of the model of the electron dynamics. The method presented applies whether radiation reaction is important or not, and whether it is classical or quantum in nature, with accuracy of a few per cent across three orders of magnitude in intensity. It is tolerant of electron beams with broad energy spread and finite divergence. In laser-electron beam collision experiments, where spatiotemporal fluctuations cause alignment of the beams to vary from shot to shot,

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04:57 Arxiv.org PhysicsLaser Trapping of Circular Rydberg Atoms. (arXiv:1911.02316v1 [physics.atom-ph])

Rydberg atoms are remarkable tools for quantum simulation and computation. They are the focus of an intense experimental activity mainly based on low-angular-momentum Rydberg states. Unfortunately, atomic motion and levels lifetime limit the experimental time-scale to about 100$\mu$s. Here, we demonstrate laser trapping of long-lived circular Rydberg states for up to 10ms. Our method is very general and opens many opportunities for quantum simulation. The 10ms trapping time corresponds to thousands of interaction cycles in a circular-state-based quantum simulator. It is also promising for quantum metrology and quantum information with Rydberg atoms.

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04:57 Arxiv.org PhysicsInformation-Driven Design for Shock Tube / Laser Absorption Studies of Fundamental Rate Constants in Combustion, with Application to Methanol Pyrolysis. (arXiv:1911.02009v1 [physics.chem-ph])

Shock tube experiments, paired with precision laser diagnostics, are ideal venues to provide kinetics data critically needed for the development, validation and optimization of modern combustion kinetics models. However, to design sensitive, accurate, feasible and information-rich experiments that may yield such data often requires sophisticated planning. This study presents a mathematical framework and quantitative approach to guide such experimental design, namely a method to pin-point the optimal conditions for specific experimentation under realistic constraints of the shock tubes and diagnostic tools involved. For demonstration purpose, the current work is focused on a key type of shock tube kinetic experiments -- direct determination of fundamental reaction rate constants. Specifically, this study utilizes a Bayesian approach to maximize the prior-posterior gain in Shannon information

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06.11.2019
18:16 RT.comRussia not joking: Unmatched hypersonic & laser weapons to be supplied to the military, Putin assures commanders

Russia won’t stop boosting its defensive capabilities with state-of-the-art weaponry, but it doesn’t mean that it’s going to threaten other countries with it, Russian President, Vladimir Putin, said. Read Full Article at RT.com

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07:33 Arxiv.org MathThe Yamada model for a self-pulsing laser: bifurcation structure for non-identical decay times of gain and absorber. (arXiv:1911.01835v1 [math.DS])

We consider self-pulsing in lasers with a gain section and an absorber section via a mechanism known as Q-switching, as described mathematically by the Yamada ordinary differential equation model for the gain, the absorber and the laser intensity. More specifically, we are interested in the case that gain and absorber decay on different time scales. We present the overall bifurcation structure by showing how the two-parameter bifurcation diagram in the plane of pump strength versus decay rate of the gain changes with the ratio between the two decay rates. In total, there are ten cases BI to BX of qualitatively different two-parameter bifurcation diagrams, which we present with an explanation of the transitions between them. Moroever, we show for each of the associated eleven cases of structurally stable phase portraits (in open regions of the parameter space) a three-dimensional

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07:33 Arxiv.org PhysicsThe Yamada model for a self-pulsing laser: bifurcation structure for non-identical decay times of gain and absorber. (arXiv:1911.01835v1 [math.DS])

We consider self-pulsing in lasers with a gain section and an absorber section via a mechanism known as Q-switching, as described mathematically by the Yamada ordinary differential equation model for the gain, the absorber and the laser intensity. More specifically, we are interested in the case that gain and absorber decay on different time scales. We present the overall bifurcation structure by showing how the two-parameter bifurcation diagram in the plane of pump strength versus decay rate of the gain changes with the ratio between the two decay rates. In total, there are ten cases BI to BX of qualitatively different two-parameter bifurcation diagrams, which we present with an explanation of the transitions between them. Moroever, we show for each of the associated eleven cases of structurally stable phase portraits (in open regions of the parameter space) a three-dimensional

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05.11.2019
18:34 WhatReallyHappened.comAlexa, Siri, Google Assistant smart speakers – they're all open to remote laser attacks

Researchers have found that MEMS microphones are so sensitive they can interpret light as sound, allowing an attacker to shoot silent commands to voice assistants from afar.

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16:00 Zdnet.comAlexa, Siri, Google Assistant smart speakers – they're all open to remote laser attacks

Researchers show smart speakers can be controlled from afar with laser beams and instructed to open smart locks and garage doors.

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15:35 Phys.orgLaser pulses create topological state in graphene

Discovering ways to control the topological aspects of quantum materials is an important research frontier because it can lead to desirable electrical and spin transport properties for future device technologies. Now MPSD scientists have discovered a pioneering laser-driven approach to generate a topological state in graphene. Their work has just been published in Nature Physics.

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12:45 Phys.orgCell chemistry illuminated by laser light

Raman microspectroscopy is a laboratory technique to produce molecular fingerprints of materials and biological specimens. However, to date fluorescence has interfered with effective application of this technique and limited its use. Now Gordon Taylor, Ph.D., a Professor in the School of Marine and Atmospheric Sciences (SoMAS) at Stony Brook University, and colleagues have devised a photochemical technique that suppresses fluorescence in sample preparation. This new technique may open the door to more efficient and highly resolved investigations of chemical distributions within individual cells. Their findings are published in Scientific Reports.

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10:12 Arxiv.org PhysicsOrientation Dependent Dissociative Ionization of H$_2$ in Strong Elliptic Laser Fields: Molecular Orientation modifies the Release-time. (arXiv:1911.01294v1 [physics.atom-ph])

We investigate the photoelectron angular emission distributions obtained by strong field dissociative ionization of H$_2$ using cold target recoil ion momentum spectroscopy. In case of employing laser light with an ellipticity close to 0.9 and an intensity of 1.0 $\times$ 10$^{14}$ W/cm$^2$, we find that the most probable release-time of the electron does not generally coincide with the time when the laser field maximizes. The release-time is affected by the molecular orientation. In addition, we observe that the width of the release-time distribution depends on molecular orientation. We attribute this observation to a two-center-interference confirming a prediction by Serov et al.

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10:12 Arxiv.org PhysicsSteering of high energy electron beam in laser plasma accelerators. (arXiv:1911.01247v1 [physics.plasm-ph])

By using Dazzler system and tilting compressor grating, we provide an effective way of using the laser group delay dispersion (GDD) to continuously steer the high energy electron beam which is accelerated by asymmetric laser-wakefield. The deviation angle of electrons is as the same as the angular chirped laser pulse from its initial optical axis, which is determined by the laser pulse-front-tilt (PFT). This unique method can be continuously used to control over the pointing direction of electron-pulses to the requisite trajectories, especially for the alignment sensitive devices such as electron-positron collider or undulator. Besides, the effect of PFT on the qualities of electron beam has been investigated.

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10:12 Arxiv.org PhysicsRectangular SNAP microresonator fabricated with a femtosecond laser. (arXiv:1911.01246v1 [physics.optics])

SNAP microresonators, which are fabricated by nanoscale effective radius variation (ERV) of the optical fiber with sub-angstrom precision, can be potentially used as miniature classical and quantum signal processors, frequency comb generators, as well as ultraprecise microfluidic and environmental optical sensors. Many of these applications require the introduction of nanoscale ERV with a large contrast {\alpha} which is defined as the maximum shift of the fiber cutoff wavelength introduced per unit length of the fiber axis. The previously developed fabrication methods of SNAP structures, which used focused CO2 and femtosecond laser beams, achieved {\alpha} ~ 0.02 nm/um. Here we develop a new fabrication method of SNAP microresonators with a femtosecond laser which allows us to demonstrate a 50-fold improvement of previous results and achieve {\alpha} ~ 1 nm/um. Furthermore, our fabrication

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10:12 Arxiv.org PhysicsCombining fiber Brillouin amplification with a repeater laser station for fiber-based optical frequency dissemination over 1400 km. (arXiv:1911.01215v1 [physics.ins-det])

We investigate optical frequency dissemination over a 1400 km long fiber link in looped configuration over a pair of underground fibers between Braunschweig and Strasbourg. This fiber link is the first to combine fiber Brillouin amplifiers with a repeater laser station. Phase-coherent operation over more than five days is demonstrated. We analyze the repeatability of the performance over four campaigns and present results of 65 days in total. The weighted mean of the fractional frequency offset of the transferred optical frequency over the complete data set is $(-1.1 \pm 0.4) \times 10^{-20}$. By analyzing the stabilization signals of the two individual fibers, the correlation of the phase noise on the two fibers is shown to be >98%.

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10:12 Arxiv.org PhysicsHigh-efficiency and high-power single-frequency fiber laser at 1.6 um based on cascaded energy-transfer pumping. (arXiv:1911.00676v1 [physics.optics])

In this paper, a technique combing cascaded energy-transfer pumping (CEP) method and master-oscillator power-amplifier (MOPA) configuration is proposed for power scaling of 1.6-um-band single-frequency fiber lasers (SFFLs), where the Er3+ ion has a limited gain. The CEP technique is fulfilled by coupling a primary signal light at 1.6 um and a C-band auxiliary laser. The numerical model of the fiber amplifier with the CEP technique reveals that the energy transfer process involves the pump competition and the in-band particle transition between the signal and auxiliary lights. Moreover, for the signal emission, the population density in the upper level is enhanced and the effective population inversion is achieved due to the CEP. A single-frequency MOPA laser at 1603 nm with an output power of 52.6 W is obtained experimentally. Besides, a slope efficiency of 30.4% is improved by more than 10%

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04.11.2019
22:28 NYT TechnologyWith a Laser, Researchers Say They Can Hack Alexa, Google Home or Siri

Researchers in Japan and at the University of Michigan said they have found a way to take over the voice-controlled digital assistants.

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05:37 Arxiv.org PhysicsRevealing laser-coherent electron features using phase-of-the-phase spectroscopy. (arXiv:1911.00477v1 [physics.atom-ph])

Phase-of-the-phase (PoP) spectroscopy is extended to two-color laser fields having a circularly counter-rotating polarization. In particular, the higher harmonics of the (two-color) phase information are analyzed in order to extract the laser-coherent part of the photoelectron spectra taken under complex target conditions. We illustrate this with a proof-of-principle simulation by considering strong-field electron emission from argon atoms within helium nanodroplets under realistic experimental conditions, i.e., a limited number of photoemission events. Multiple elastic scattering on neutral helium atoms creates a laser-incoherent background, but the higher harmonics of the PoP-signal allow to resolve the coherent contribution to the photoemission.

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05:37 Arxiv.org PhysicsElectron rotational asymmetry in strong-field photodetachment from F$^-$ by circularly polarized laser pulses. (arXiv:1911.00290v1 [physics.atom-ph])

We use the $R$-matrix with time-dependence method to study detachment from F$^-$ in circularly-polarized laser fields of infrared wavelength. By decomposing the photoelectron momentum distribution into separate contributions from detached $2p_1$ and $2p_{-1}$ electrons, we demonstrate that the detachment yield is distributed asymmetrically with respect to these initial orbitals. We observe the well-known preference for strong-field detachment of electrons that are initially counter-rotating relative to the field, and calculate the variation in this preference as a function of photoelectron energy. The wavelengths used in this work provide natural grounds for comparison between our calculations and the predictions of analytical approaches tailored for the strong-field regime. In particular, we compare the ratio of counter-rotating electrons to corotating electrons as a function of

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03.11.2019
20:26 Technology.orgHow to Laser-Cut 3D Objects

With a 3d printer, it is straightforward to create complex 3d shapes. However, the problem is that you

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01.11.2019
06:35 Arxiv.org PhysicsGeneration and Characterization of Attosecond Micro-Bunched Electron Pulse Trains via Dielectric Laser Acceleration. (arXiv:1910.14343v1 [physics.acc-ph])

Dielectric laser acceleration is a versatile scheme to accelerate and control electrons with the help of femtosecond laser pulses in nanophotonic structures. We demonstrate here the generation of a train of electron pulses with individual pulse durations as short as $270\pm80$ attoseconds(FWHM), measured in an indirect fashion, based on two subsequent dielectric laser interaction regions connected by a free-space electron drift section, all on a single photonic chip. In the first interaction region (the modulator), an energy modulation is imprinted on the electron pulse. During free propagation, this energy modulation evolves into a charge density modulation, which we probe in the second interaction region (the analyzer). These results will lead to new ways of probing ultrafast dynamics in matter and are essential for future laser-based particle accelerators on a photonic chip.

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06:35 Arxiv.org PhysicsLaser-free trapped-ion entangling gates with simultaneous insensitivity to qubit and motional decoherence. (arXiv:1910.14178v1 [quant-ph])

The dominant error sources for state-of-the-art laser-free trapped-ion entangling gates are decoherence of the qubit state and motion. The effect of these decoherence mechanisms can be suppressed with additional control fields, or through other techniques that reduce gate speed. Here, we propose using a near-motional-frequency magnetic field gradient to make a laser-free gate that is simultaneously resilient to both types of decoherence, does not require additional control fields, and has a relatively smaller cost in gate speed.

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31.10.2019
09:19 Arxiv.org PhysicsCharacterization of a supersonic gas jet via laser-induced photoelectron ionization. (arXiv:1910.13950v1 [physics.ins-det])

We describe the characterization of a pulsed supersonic rare gas beam which is intended to serve as an ultracold neutral atom target for the production of an ultrashort ion pulse via femtosecond photoionization. The velocity distribution of atoms entrained in the beam is measured and characterized by temperatures $T_\parallel$ and $T_\perp$ in directions along and perpendicular to the beam propagation, respectively. It is shown that $T_\perp$ values in the mK regime are achieved at distances of the order of 1000 mm from the nozzle. Moreover, the center beam density at this position is measured to be of the order of $10^{11} atoms/cm^{3}$. Both findings are essential for the intended application and confirm the targeted beam specifications. Comparison with theoretical estimates reveals the well-known skimmer interference effect, which is found to reduce the beam density by more than one order

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09:19 Arxiv.org PhysicsLaser-produced magnetic-Rayleigh-Taylor unstable plasma slabs in a 20 T magnetic field. (arXiv:1910.13778v1 [physics.plasm-ph])

Magnetized laser-produced plasmas are central to many novel laboratory astrophysics and inertial confinement fusion studies, as well as in industrial applications. Here we provide the first complete description of the three-dimensional dynamics of a laser-driven plasma plume expanding in a 20 T transverse magnetic field. The plasma is collimated by the magnetic field into a slender, rapidly elongating slab, whose plasma-vacuum interface is unstable to the growth of the "classical", fluid-like magnetized Rayleigh-Taylor instability.

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09:19 Arxiv.org PhysicsExtreme nonlinear Raman interaction of an ultrashort nitrogen ion laser with an impulsively excited molecular wavepacket. (arXiv:1910.13596v1 [physics.optics])

We report generation of cascaded rotational Raman scattering up to 58th orders in coherently excited CO_2 molecules. The high-order Raman scattering, which produces a quasiperiodic frequency comb with more than 600 sidebands, is obtained using an intense femtosecond laser to impulsively excite rotational coherence and the femtosecond-laser-induced N_2^+ lasing to generate cascaded Raman signals. The novel configuration allows this experiment to be performed with a single femtosecond laser beam at free-space standoff locations. It is revealed that the efficient spectral extension of Raman signals is attributed to the specific spectra-temporal structures of N_2^+ lasing, the ideal spatial overlap of femtosecond laser and N2+ lasing, and the guiding effect of molecular alignment. The Raman spectrum extending above 2000 cm^-1 naturally corresponds to a femtosecond pulse train due to the periodic

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30.10.2019
04:51 Arxiv.org PhysicsFemtometer-resolved simultaneous measurement of multiple laser wavelengths in a speckle wavemeter. (arXiv:1910.13411v1 [physics.optics])

Many areas of optical science require an accurate measurement of optical spectra. Devices based on laser speckle promise compact wavelength measurement, with attometer-level sensitivity demonstrated for single wavelength laser fields. The measurement of multimode spectra using this approach would be attractive, yet this is currently limited to picometer resolution. Here, we present a method to improve the resolution and precision of speckle-based multi-wavelength measurements. We measure multiple wavelengths simultaneously, in a device comprising a single 1 m-long step-index multimode fiber and a fast camera. Independent wavelengths separated by as little as 1 fm are retrieved with 0.2 fm precision using Principal Component Analysis. The method offers a viable way to measure sparse spectra containing multiple individual lines and is likely to find application in the tracking of multiple

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04:51 Arxiv.org PhysicsFloquet topological insulator laser. (arXiv:1910.13363v1 [physics.optics])

We introduce a class of topological lasers based on the photonic Floquet topological insulator concept. The proposed system is realized as a truncated array of the lasing helical waveguides, where the pseudo-magnetic field arises due to twisting of the waveguides along the propagation direction that breaks the time-reversal symmetry and opens up a topological gap. When sufficient gain is provided in the edge channels of the array then the system lases into the topological edge states. Topological lasing is stable only in certain intervals of the Bloch momenta, that ensure a dynamic, but stable balance between the linear amplification and nonlinear absorption leading to the formation of the breathing edge states. We also illustrate topological robustness of the edge currents by simulating lattice defects and triangular arrangements of the waveguides.

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04:51 Arxiv.org PhysicsLaser-induced dynamics of molecules with strong nuclear quadrupole coupling. (arXiv:1910.13275v1 [physics.atm-clus])

We present a general variational approach for computing the laser-induced rovibrational dynamics of molecules taking into account the hyperfine effects of the nuclear quadrupole coupling. The method combines the general variational approach TROVE, which provides accurate rovibrational hyperfine energies and wave functions for arbitrary molecules, with the variational method RichMol, designed for generalized simulations of the rovibrational dynamics in the presence of external electric fields. We investigate the effect of the nuclear quadrupole coupling on the short-pulse laser alignment of a prototypical molecule CFClBrI, which contains nuclei with large quadrupole constants. The influence of the nuclear quadrupole interactions on the post-pulse molecular dynamics is negligible at early times, first several revivals, however at longer timescales the effect is entirely detrimental and strongly

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04:51 Arxiv.org PhysicsExperimental observation and computational modeling of radial Weibel instability in high intensity laser-plasma interactions. (arXiv:1910.12940v1 [physics.plasm-ph])

When a relativistic intensity laser interacts with the surface of a solid density target, suprathermal electron currents are subject to Weibel instability filamentation when propagating through the thermal population of the bulk target. We present time resolved shadowgraphy of radial ionization front expansion and Weibel instability filamentation within a thin, sub-micron, sheet initiated by irradiation with a short pulse, high intensity laser. High temporal (100 fs) and spatial (1 $\mu$m) resolution shadowgraphy of the interaction reveals a relativistic expansion of the ionization front within a 120 $\mu$m diameter region surrounding the laser-target interaction, corroborated by simulations to expand at $0.77c$, where $c$ is the speed of light. Filamentation within the patch persists for several picoseconds and seeds the eventual recombination and heating dynamics on the nanosecond

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04:51 Arxiv.org PhysicsMathieu-Gauss diffraction of a multi segment-shaped laser beam. (arXiv:1910.12938v1 [physics.optics])

We studied the field structure on diffraction of a multi segment shaped laser beam. Diffraction of a laser beam with the shape of the multi circular segments was investigated.

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29.10.2019
07:38 Arxiv.org MathMathematical Modeling of Vaporization during Laser-Induced Thermotherapy in Liver Tissue. (arXiv:1910.12515v1 [math.AP])

Laser-induced thermotherapy (LITT) is a minimally invasive method causing tumor destruction due to heat ablation and coagulative effects. Computer simulations can play an important role to assist physicians with the planning and monitoring of the treatment. Our recent study with ex-vivo porcine livers has shown that the vaporization of the water in the tissue must be taken into account when modeling LITT. We extend the model used for simulating LITT to account for vaporization using two different approaches. Results obtained with these new models are then compared with the measurements from the original study.

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07:38 Arxiv.org PhysicsPump depletion and hot electron generation in long density scale length plasma with shock ignition high intensity laser. (arXiv:1910.12323v1 [physics.plasm-ph])

Two-dimension Particle-in-cell simulations for laser plasma interaction with laser intensity of $10^{16} W/cm^2$, plasma density range of 0.01-0.28$n_c$ and scale length of $230 -330 \mu m$ showed significant pump depletion of the laser energy due to stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) in the low density region ($n_e=0.01-0.2 n_c$). The simulations identified hot electrons generated by SRS in the low density region with moderate energy and by two-plasmon-decay (TPD) near $n_e=0.25n_c$ with higher energy. The overall hot electron temperature (46 keV) and conversion efficiency (3%) were consistent with the experiment measurements. The simulations also showed artificially reducing SBS would lead to stronger SRS and a softer hot electron spectrum.

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28.10.2019
21:22 Technology.orgEndurance Lasers announces 11-th giveaway: One more chance to win a 10-watt laser module

Endurance Lasers, specialists in the field of high-power laser cutting and engraving equipment, have just announced their new

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17:18 Phys.orgResearchers transmit energy with laser in 'historic' power-beaming demonstration

It was the second day of a three-day-long tech demonstration at the David Taylor Model Basin at the Naval Surface Warfare Center in Bethesda, Maryland, where attendees had gathered to stand around in the dark to look at something they mostly couldn't see.

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10:07 Arxiv.org PhysicsKnowledge of Process-Structure-Property Relationships to Engineer Better Heat Treatments for Laser Powder Bed Fusion Additive Manufactured Inconel 718. (arXiv:1909.12290v2 [physics.app-ph] UPDATED)

Dislocation structures, chemical segregation, {\gamma ^{\prime}, {\gamma ^{\prime \prime}}, {\delta} precipitates and Laves phase were quantified within the microstructures of Inconel 718 (IN718) produced by laser powder bed fusion additive manufacturing (AM) and subjected to standard, direct aging, and modified multi-step heat treatments. Additionally, heat-treated samples still attached to the build plates vs. those removed were also documented for a standard heat treatment. The effects of the different resulting microstructures on room temperature strengths and elongations to failure is revealed. Knowledge derived from these process structure property relationships was used to engineer a super solvus solution anneal at 1020 degC for 15 minutes, followed by aging at 720 degC for 24 hours heat treatment for AM-IN718 that eliminates Laves and {\delta} phases, preserves AM specific dislocation

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25.10.2019
17:57 Phys.orgRetrieving physical properties from two-colour laser experiments

When photons of light interact with particles of matter, a diverse variety of physical processes can unfold in ultrafast timescales. To explore them, physicists currently use 'two-colour pump-probe' experiments, in which an ultrashort, infrared laser pulse is first fired at a material, causing its constituent electrons to move. After a controllable delay, this pulse is followed by a train of similarly short, extreme-ultraviolet pulses, ionising the material.

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17:51 ScienceDaily.comRetrieving physical properties from two-color laser experiments

Analytical and numerical analysis gives the first indications of how physically useful information can be extracted from two-colour pump probe experiments, and how it can be distinguished from the signatures arising from the initial infrared laser, according to a new article.

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16:41 Phys.orgRapid laser solver for the phase retrieval problem

Physicists can explore tailored physical systems to rapidly solve challenging computational tasks by developing spin simulators, combinatorial optimization and focusing light through scattering media. In a new report on Science Advances, C. Tradonsky and a group of researchers in the Departments of Physics in Israel and India addressed the phase retrieval problem by reconstructing an object from its scattered intensity distribution. The experimental process addressed an existing problem in disciplines ranging from X-ray imaging to astrophysics that lack techniques to reconstruct an object of interest, where scientists typically use indirect iterative algorithms that are inherently slow.

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04:04 Arxiv.org PhysicsLaser-Cooled Polyatomic Molecules for Improved Electron Electric Dipole Moment Searches. (arXiv:1910.11318v1 [physics.atom-ph])

Doppler and Sisyphus cooling of $^{174}$YbOH are achieved and studied. This polyatomic molecule has high sensitivity to physics beyond the Standard Model and represents a new class of species for future high-precision probes of new T-violating physics. The transverse temperature of the YbOH beam is reduced by nearly two orders of magnitude to $< 600 \, \mu$K and the phase-space density is increased by a factor of $>6$ via Sisyphus cooling. We develop a full numerical model of the laser cooling of YbOH and find excellent agreement with the data. We project that laser cooling and magneto-optical trapping of long-lived samples of YbOH molecules are within reach and these will allow a high sensitivity probe of the electric dipole moment (EDM) of the electron. The approach demonstrated here is easily generalized to other isotopologues of YbOH that have enhanced sensitivity to other

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04:04 Arxiv.org PhysicsGamma ray emission via an ultrahigh intensity laser pulse interaction with a laser-wakefield accelerated electron beam. (arXiv:1910.10891v1 [physics.plasm-ph])

We investigate a method to generation of $\gamma$ ray photons in collision of an ultrahigh intensity laser pulse with a laser-wakefield accelerated electron beam. We consider the composed target of a homogeneous underdense preplasma in front of an ultrathin solid foil. By using of two dimensional particle-in-cell simulations, we show that the electrons in the underdense plasma are trapped and accelerated by the laser wakefield. When the laser pulse is reflected by the thin solid foil, the wakefield accelerated electron beam continue to move forward and passing through the target almost without the influence of the reflected laser pulse and the foil. Consequently, two groups of $\gamma$ ray flashes are generated by the wakefield accelerated electron beam interacting with the reflected laser pulse in front of the foil as well as interacting another counter propagating pitawatt laser pulse in

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04:04 Arxiv.org PhysicsDeep learning enabled laser speckle wavemeter with a high dynamic range. (arXiv:1910.10702v1 [physics.optics])

The speckle pattern produced when a laser is scattered by a disordered medium has recently been shown to give a surprisingly accurate or broadband measurement of wavelength. Here we show that deep learning is an ideal approach to analyse wavelength variations using a speckle wavemeter due to its ability to identify trends and overcome low signal to noise ratio in complex datasets. This combination enables wavelength measurement at high resolution and over a broad operating range in a single step, which has not been possible with previous approaches. We demonstrate attometre-scale wavelength resolution over an operating range from 488 nm to 976 nm. This dynamic range is six orders of magnitude beyond the state of the art.

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04:04 Arxiv.org CSA Maximum Likelihood Approach to Extract Finite Planes from 3-D Laser Scans. (arXiv:1910.11146v1 [cs.RO])

Whether it is object detection, model reconstruction, laser odometry, or point cloud registration: Plane extraction is a vital component of many robotic systems. In this paper, we propose a strictly probabilistic method to detect finite planes in organized 3-D laser range scans. An agglomerative hierarchical clustering technique, our algorithm builds planes from bottom up, always extending a plane by the point that decreases the measurement likelihood of the scan the least. In contrast to most related methods, which rely on heuristics like orthogonal point-to-plane distance, we leverage the ray path information to compute the measurement likelihood. We evaluate our approach not only on the popular SegComp benchmark, but also provide a challenging synthetic dataset that overcomes SegComp's deficiencies. Both our implementation and the suggested dataset are available at

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04:04 Arxiv.org CSA Maximum Likelihood Approach to Extract Polylines from 2-D Laser Range Scans. (arXiv:1910.10711v1 [cs.RO])

Man-made environments such as households, offices, or factory floors are typically composed of linear structures. Accordingly, polylines are a natural way to accurately represent their geometry. In this paper, we propose a novel probabilistic method to extract polylines from raw 2-D laser range scans. The key idea of our approach is to determine a set of polylines that maximizes the likelihood of a given scan. In extensive experiments carried out on publicly available real-world datasets and on simulated laser scans, we demonstrate that our method substantially outperforms existing state-of-the-art approaches in terms of accuracy, while showing comparable computational requirements. Our implementation is available under https://github.com/acschaefer/ple.

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04:04 Arxiv.org CSDeep learning enabled laser speckle wavemeter with a high dynamic range. (arXiv:1910.10702v1 [physics.optics])

The speckle pattern produced when a laser is scattered by a disordered medium has recently been shown to give a surprisingly accurate or broadband measurement of wavelength. Here we show that deep learning is an ideal approach to analyse wavelength variations using a speckle wavemeter due to its ability to identify trends and overcome low signal to noise ratio in complex datasets. This combination enables wavelength measurement at high resolution and over a broad operating range in a single step, which has not been possible with previous approaches. We demonstrate attometre-scale wavelength resolution over an operating range from 488 nm to 976 nm. This dynamic range is six orders of magnitude beyond the state of the art.

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24.10.2019
06:46 Arxiv.org PhysicsLaser Cooling of Silica Glass. (arXiv:1910.10609v1 [physics.optics])

Laser cooling of a solid is achieved when a coherent laser illuminates the material in the red tail of its absorption spectrum, and the heat is carried out by anti-Stokes fluorescence of the blue-shifted photons. Solid-state laser cooling has been successfully demonstrated in several materials, including rare-earth-doped crystals and glasses. Silica glass, being the most widely used optical material, has so far evaded all laser cooling attempts. In addition to its fundamental importance, many potential applications can be conceived for anti-Stokes fluorescence cooling of silica. These potential applications range from the substrate cooling of optical circuits for quantum information processing and cryogenic cooling of mirrors in high-sensitivity interferometers for gravitational wave detection to the heating reduction in high-power fiber lasers and amplifiers. Here we report the net cooling

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06:46 Arxiv.org PhysicsThe pure-quartic soliton laser. (arXiv:1910.10314v1 [physics.optics])

The generation of ultrashort pulses hinges on the careful management of dispersion. Traditionally, this has exclusively involved second-order dispersion, while higher-order dispersion was treated as a nuisance to be minimized. Here we show that high-order dispersion can be strategically leveraged to access an uncharted regime of ultrafast laser operation. In particular, we demonstrate a mode-locked laser, with an intra-cavity spectral pulse-shaper, that emits pure-quartic soliton pulses, which arise from the interaction of the fourth-order dispersion and the Kerr nonlinearity. Using phase-resolved measurements we demonstrate that the energy of these pulses is proportional to the third power of the inverse pulse duration. This implies a dramatic increase in the energy of ultrashort pulses compared to those emitted by soliton lasers to date. These results not only demonstrate a novel approach

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23.10.2019
09:31 Arxiv.org PhysicsPost-Heat Treatment Design of High-Strength Low-Alloy Steels Processed by Laser Powder Bed Fusion. (arXiv:1910.09939v1 [cond-mat.mtrl-sci])

In this study, a post-heat treatment design for additively manufactured copper-bearing high-strength low-alloy (HSLA)-100 steel is performed by understanding the process-structure-property relationships. Hot isostatic pressing (HIP) is designed to reduce the porosity from 3% to less than 1% for the HSLA-100 steel processed by laser powder bed fusion (LPBF). Quenching dilatometry is employed to design the HIP parameters with the optimized cooling rate for the maximum amount of martensite transformed after HIP. Afterward, a post-heat treatment step with cyclic re-austenitization is introduced for an effective grain refinement to compensate the coarsened microstructure after HIP. Finally, tempering is optimized through microstructure characterization and microhardness. A two-fold increase in the yield strength of the HSLA with tailored microstructure during post-heat treatment is achieved in

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22.10.2019
05:00 Arxiv.org MathIdentification of the Blood Perfusion Rate for Laser-Induced Thermotherapy in the Liver. (arXiv:1910.09199v1 [math.OC])

Using PDE-constrained optimization we introduce a parameter identification approach which can identify the blood perfusion rate from MR thermometry data obtained during the treatment with laser-induced thermotherapy (LITT). The blood perfusion rate, i.e., the cooling effect induced by blood vessels, can be identified during the first stage of the treatment. This information can then be used by a simulation to monitor and predict the ongoing treatment. The approach is tested with synthetic measurements with and without artificial noise as input data.

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05:00 Arxiv.org PhysicsXPM-forced frequency-oscillating soliton in mode-locked fiber laser. (arXiv:1910.09225v1 [physics.optics])

Cross phase modulation (XPM) could induce soliton trapping in nonlinear medium, which has been employed to achieve vector soliton, optical switching and optical analog of gravity-like potentials. These results are generally within the definition in Hamilton system. Here, we report on the observation of a XPM-forced frequency-oscillating soliton (XFOS) whose wavelength exhibits redshift and blueshift periodically like dancing in a mode-locked fiber laser under moderate birefringence. XFOS consists of two orthogonally polarized components exhibiting simultaneous frequency oscillation driven by XPM and gain effect, which allows withstanding higher pulse energy. The pulse trapping is maintained by differentiating the frequency-shift rate. Numerical simulations agree very well with experimental results, revealing an idiosyncratic evolution dynamic for asymmetry pulses in nonlinear dissipative

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05:00 Arxiv.org PhysicsUltrafast energy absorption and photoexcitation of bulk plasmon in crystalline silicon subjected to intense ultrashort laser pulses. (arXiv:1910.09023v1 [physics.optics])

We investigate the non-linear response and energy absorption in bulk silicon irradiated by intense 12fs near-infrared laser pulses. Depending on the laser intensity, we distinguish two regimes of non-linear absorption of the laser energy: for low intensities, energy deposition and photoionization involve perturbative three-photon transition through the direct bandgap of silicon. For laser intensities near and above $10^{14}$ W/cm$^2$, corresponding to photocarrier density of order 10$^{22}$ cm$^{-3}$, we find that absorption at near-infrared wavelengths is greatly enhanced due to excitation of bulk plasmon resonance. In this regime, the energy deposited onto electrons exceeds a few times the thermal melting threshold of Si. The optical reflectivity of the photoexcited solid is found in good qualitative agreement with existing experimental data. In particular, the model predicts that the main

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05:00 Arxiv.org PhysicsLaser ablation in liquid: bridge from a plasma stage to bubble formation. (arXiv:1910.08924v1 [physics.comp-ph])

Laser ablation through liquid is an important process that have to be studied for applications which use laser ablation in liquid (LAL) and laser shock peening (LSP). LAL is employed for production of suspensions of nanoparticles, while LSP is applied to increase hardness and fatique/corrosion resistance properties of a surface layer. A bubble appears in liquid around the laser spot focused at a target surface after strong enough laser pulse. In the paper we connect the early quasi-plane heated layer created by a pulse in liquid and the bubble forming at much later stages. In the previous works these early stage from one side and the late stage from another side existed mainly as independent entities. At least, quantitative links between them were unknown. We consider how the quasi-plane heated layer of liquid forms thank to thermal conduction, how gradually conduction becomes weaker, and how

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21.10.2019
07:34 Arxiv.org PhysicsSpectral and spatial shaping of laser-driven proton beams using a pulsed high-field magnet beamline. (arXiv:1910.08430v1 [physics.acc-ph])

Intense laser-driven proton pulses, inherently broadband and highly divergent, pose a challenge to established beamline concepts on the path to application-adapted irradiation field formation, particularly for 3D. Here we experimentally show the successful implementation of a highly efficient (50% transmission) and tuneable dual pulsed solenoid setup to generate a homogeneous (8.5% uniformity laterally and in depth) volumetric dose distribution (cylindrical volume of 5 mm diameter and depth) at a single pulse dose of 0.7 Gy via multi-energy slice selection from the broad input spectrum. The experiments have been conducted at the Petawatt beam of the Dresden Laser Acceleration Source Draco and were aided by a predictive simulation model verified by proton transport studies. With the characterised beamline we investigated manipulation and matching of lateral and depth dose profiles to various

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07:34 Arxiv.org PhysicsEngineering quantum wave-packet dispersion with a strong non-resonant femtosecond laser pulse. (arXiv:1910.08241v1 [physics.optics])

A non-dispersing wave packet has been attracting much interest from various scientific and technological viewpoints. However, most quantum systems are accompanied by anharmonicity, so that retardation of quantum wave-packet dispersion is limited to very few examples only under specific conditions and targets. Here we demonstrate a conceptually new and universal method to retard or advance the dispersion of a quantum wave packet through programmable time shift induced by a strong non-resonant femtosecond laser pulse. A numerical simulation has verified that a train of such retardation pulses stops wave-packet dispersion.

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07:34 Arxiv.org PhysicsUltra-narrow linewidth hybrid integrated semiconductor laser. (arXiv:1910.08141v1 [physics.optics])

We demonstrate a hybrid integrated and widely tunable diode laser with an intrinsic linewidth as narrow as 40 Hz, achieved with a single roundtrip through a low-loss feedback circuit that extends the cavity length to 0.5 meter on a chip. Employing solely dielectrics for single-roundtrip, single-mode resolved feedback filtering enables linewidth narrowing with increasing laser power, without limitations through nonlinear loss. We achieve single-frequency oscillation with up to 23 mW fiber coupled output power, 70-nm wide spectral coverage in the 1.55 $\mu$m wavelength range with 3 mW output, and obtain more than 60 dB side mode suppression. Such properties and options for further linewidth narrowing render the approach of high interest for direct integration in photonic circuits serving microwave photonics, coherent communications, sensing and metrology with highest resolution.

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07:34 Arxiv.org PhysicsUltrafast-laser-absorption spectroscopy for single-shot, mid-infrared measurements of temperature, CO, and CH$_4$ in flames. (arXiv:1910.08116v1 [physics.app-ph])

This manuscript describes the development of an ultrafast (i.e.,femtosecond), mid-infrared, laser-absorption diagnostic and its initial application to measuring temperature, CO, and CH$_4$ in flames. The diagnostic employs a Ti:Sapphire oscillator emitting 55-fs pulses near 800 nm which were amplified and converted into the mid-infrared (mid-IR) though optical parametric amplification (OPA) at a repetition rate of 5 kHz. The pulses were directed through the test gas and into a high-speed mid-infrared spectrograph to image spectra across a $\approx$30 nm bandwidth with a spectral resolution of $\approx$0.3 nm. Gas properties were determined by least-squares fitting a spectroscopic model to measured single-shot absorbance spectra. The diagnostic was validated with measurements of temperature, CO, and CH$_4$ in a static-gas cell with an accuracy of 0.7% to 1.8% of known values. Single-shot, 5

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18.10.2019
07:54 Arxiv.org MathStochastic Geometry-Based Analysis of Airborne Base Stations with Laser-powered UAVs. (arXiv:1910.07794v1 [cs.IT])

One of the most promising solutions to the problem of limited flight time of unmanned aerial vehicles (UAVs), is providing the UAVs with power through laser beams emitted from Laser Beam Directors (LBDs) deployed on the ground. In this letter, we study the performance of a laser-powered UAV-enabled communication system using tools from stochastic geometry. We first derive the energy coverage probability, which is defined as the probability of the UAV receiving enough energy to ensure successful operation (hovering and communication). Our results show that to ensure energy coverage, the distance between the UAV and its dedicated LBD must be below a certain threshold, for which we derive an expression as a function of the system parameters. Considering simultaneous information and power transmission through the laser beam using power splitting technique, we also derive the joint energy and the

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07:54 Arxiv.org PhysicsSingle-Shot Multi-Stage Damage and Ablation of Silicon by Femtosecond Mid-infrared Laser Pulses. (arXiv:1910.07953v1 [cond-mat.mtrl-sci])

Although ultrafast laser materials processing has advanced at a breakneck pace over the last two decades, most applications have been developed with laser pulses at near-IR or visible wavelengths. Recent progress in mid-infrared (MIR) femtosecond laser source development may create novel capabilities for material processing. This is because, at high intensities required for such processing, wavelength tuning to longer wavelengths opens the pathway to a special regime of laser-solid interactions. Under these conditions, due to the ${\lambda}^2$ scaling, the ponderomotive energy of laser-driven electrons may significantly exceed photon energy, band gap and electron affinity and can dominantly drive absorption, resulting in a paradigm shift in the traditional concepts of ultrafast laser-solid interactions. Irreversible high-intensity ultrafast MIR laser-solid interactions are of primary interest

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07:54 Arxiv.org PhysicsCoherence transfer in an akinetic swept source OCT laser with optical feedback. (arXiv:1910.07791v1 [physics.optics])

We theoretically investigate the influence of optical feedback onto the dynamics of a semiconductor swept source laser. In particular, we show that optical feedback can be used to lock the phase of the successive lasing modes of a multi-section semiconductor laser commonly used for Optical Coherence Tomography (OCT) applications. We also identify two different regimes called sliding frequency self-mixing and sliding frequency mode-locking. The second regime demonstrates sub-nanosecond sliding frequency pulses for non-linear optics applications.

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07:54 Arxiv.org CSStochastic Geometry-Based Analysis of Airborne Base Stations with Laser-powered UAVs. (arXiv:1910.07794v1 [cs.IT])

One of the most promising solutions to the problem of limited flight time of unmanned aerial vehicles (UAVs), is providing the UAVs with power through laser beams emitted from Laser Beam Directors (LBDs) deployed on the ground. In this letter, we study the performance of a laser-powered UAV-enabled communication system using tools from stochastic geometry. We first derive the energy coverage probability, which is defined as the probability of the UAV receiving enough energy to ensure successful operation (hovering and communication). Our results show that to ensure energy coverage, the distance between the UAV and its dedicated LBD must be below a certain threshold, for which we derive an expression as a function of the system parameters. Considering simultaneous information and power transmission through the laser beam using power splitting technique, we also derive the joint energy and the

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17.10.2019
23:41 ScienceDaily.comWeaving quantum processors out of laser light

Researchers open a new avenue to quantum computing with a breakthrough experiment: a large-scale quantum processor made entirely of light.

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21:06 Phys.orgWeaving quantum processors out of laser light

An international team of scientists from Australia, Japan and the United States has produced a prototype of a large-scale quantum processor made of laser light.

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10:30 Arxiv.org PhysicsIncreasing the accuracy of laser flash analysis using noise-robust numerical algorithms in PULsE. (arXiv:1910.07499v1 [physics.app-ph])

The laser flash method is highly regarded due to its applicability to a wide temperature range, from cryogenic temperatures to the melting point of refractory metals, and to extreme environments involving radioactive or hazardous materials. Although instruments implementing this method are mostly produced on a commercial basis by major manufacturers, there is always room for improvement both in terms of experimental methods and data treatment procedures. The measurement noise, either due to the detector performance or electromagnetic interferences, presents a significant problem when accurate determination of thermal properties is desired. Noise resilience of the laser flash method is rarely mentioned in published literature; there are currently no data treatment procedures which could guarantee adequate performance under any operating conditions. In this paper, a computational framework

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10:30 Arxiv.org PhysicsLIPSS on thin metallic films: New insights from multiplicity of laser-excited electromagnetic modes and efficiency of metal oxidation. (arXiv:1910.07280v1 [physics.app-ph])

Thin Cr films 28-nm thick deposited on glass substrates were processed by scanning low-intensity femtosecond laser pulses with energy well below single-pulse damage threshold. Two types of laser-induced periodic surface structures (LIPSS) were produced, depending on the scanning velocity, (1) parallel to laser light polarization with periodicity somewhat smaller than laser wavelength and (2) perpendicular to polarization with spatial period much smaller than wavelength. All structures are formed as protrusions above the initial film surface and exhibit a high degree of oxidation. To explain formation of the LIPSS and their conversion from one to another type, a rigorous numerical approach for modeling surface electromagnetic waves in thin-film geometry has been developed, which takes into account the change of optical properties of material due to laser-induced oxidation and porosity. The

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10:30 Arxiv.org PhysicsErbium-doped aluminophosphosilicate all-fiber laser operating at 1584 nm. (arXiv:1910.07008v1 [physics.optics])

We report on an ytterbium-free erbium-doped aluminophosphosilicate all-fiber laser, producing an output power of 25 W at a wavelength of 1584 nm with a slope efficiency of 30% with respect to the 976 nm absorbed pump power. The simple cavity design proposed takes advantage of fiber Bragg gratings written directly in the gain fiber. The single-mode erbium-doped aluminophosphosilicate fiber was fabricated in-house and was doped with 0.06 mol.% of Er2O3, 1.77 mol.% of Al2O3 and 1.04 mol.% of P2O5. The incorporation of aluminium and phosphorus into the fiber core allowed for an increased concentration of erbium without inducing significant clustering, while keeping the numerical aperture low to ensure a single-mode laser operation.

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16.10.2019
06:12 Arxiv.org PhysicsLaser-induced surface relief nanocrowns as a manifestation of nanoscale Rayleigh-Plateau hydrodynamic instability. (arXiv:1910.06702v1 [physics.app-ph])

Nanoscale hydrodynamic instability of ring-like molten rims around ablative microholes produced in nanometer-thick gold films by tightly focused nanosecond-laser pulses was experimentally explored in terms of laser pulse energy and film thickness. These parametric dependencies of basic instability characteristics - order and period of the resulting nanocrowns - were analyzed, revealing its apparently Rayleigh-Plateau character, as compared to much less consistent possible van der Waals and impact origins. Along with fundamental importance, these findings will put forward pulsed laser ablation as an alternative facile inexpensive table-top approach to study such hydrodynamic instabilities developing at nanosecond temporal and nanometer spatial scales.

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15.10.2019
08:59 Arxiv.org PhysicsA single-laser alternating-frequency magneto-optical trap. (arXiv:1910.05540v1 [physics.atom-ph])

In this paper, we present a technique for magneto-optical cooling and trapping of neutral atoms using a single laser. The alternating-frequency magneto-optical trap (AF-MOT) uses an agile light source that sequentially switches between cooling and repumping transition frequencies by tuning the injection current of the laser diode. We report on the experimental demonstration of such a system for 87Rb and 85Rb based on a micro-integrated extended cavity diode laser (ECDL) performing laser frequency jumps of up to 6.6 GHz with a tuning time in the microsecond regime and a repetition rate of up to 7.6 kHz. For that, a combination of a feed-forward for coarse frequency control and a feedback for precise locking was used. We discuss the results of the AF-MOT characterization in terms of atom numbers and cloud temperature for different operation parameters.

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14.10.2019
04:36 Arxiv.org PhysicsX-ray assisted nuclear excitation by electron capture in optical laser-generated plasmas. (arXiv:1910.05326v1 [physics.plasm-ph])

X-ray assisted nuclear excitation by electron capture (NEEC) into inner-shell atomic holes in a plasma environment generated by strong optical lasers is investigated theoretically. The considered scenario involves the interaction of a strong optical laser with a solid-state nuclear target leading to the generation of a plasma. In addition, intense x-ray radiation from an x-ray free electron laser (XFEL) produces inner-shell holes in the plasma ions, into which NEEC may occur. As case study we consider the $4.85$-keV transition starting from the 2.4 MeV long-lived $^{\mathrm{93m}}$Mo isomer that can be used to release the energy stored in this metastable nuclear state. We find that the recombination into $2p_{1/2}$ inner-shell holes is most efficient in driving the nuclear transition. Already at few hundred eV plasma temperature, the generation of inner-shell holes can allow optimal conditions

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04:36 Arxiv.org PhysicsCharge coupling in multi-stage laser wakefield acceleration. (arXiv:1910.04977v1 [physics.acc-ph])

The multi-stage technique for laser driven acceleration of electrons become a critical part of full-optical, jitter-free accelerators. Use of several independent laser drivers and shorter length plasma targets allows the stable and reproducible acceleration of electron bunches (or beam) in the GeV energies with lower energy spreads. At the same time the charge coupling, necessary for efficient acceleration in the consecutive acceleration stage(s), depends collectively on the parameters of the injected electron beam, the booster stage, and the non-linear transverse dynamics of the electron beam in the laser pulse wake. An unmatched electron beam injected in the booster stage(s), and its non-linear transverse evolution may result in perturbation and even reduction of the field strength in the acceleration phase of the wakefield. Analysis and characterization of charge coupling in multi-stage

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04:36 Arxiv.org PhysicsCombined molecular dynamics and quantum trajectories simulation of laser-driven, collisional systems. (arXiv:1910.04837v1 [physics.atom-ph])

We introduce a combined molecular dynamics (MD) and quantum trajectories (QT) code to simulate the effects of near-resonant optical fields on state-vector evolution and particle motion in a collisional system. In contrast to collisionless systems, in which the quantum dynamics of multi-level, laser-driven particles with spontaneous emission can be described with the optical Bloch equations (OBEs), particle velocities in sufficiently collisional systems change on timescales comparable to those of the laser-induced, quantum-state dynamics. These transient velocity changes can cause the time-averaged velocity dependence of the quantum state to differ from the OBE solution. We use this multiscale code to describe laser-cooling in a strontium ultracold neutral plasma. Important phenomena described by the simulation include suppression of electromagnetically induced transparencies through rapid

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04:36 Arxiv.org PhysicsDirect Laser Writing of Birefringent Photonic Crystals for the Infrared Spectral Range. (arXiv:1910.04826v1 [physics.app-ph])

Infrared optical photonic crystals fabricated using direct laser writing, which is based on the two-photon polymerization of suitable monomers, have received substantial interest since the emergence of this process. Two-photon polymerization could be a disruptive technology for the fabrication of all-dielectric photonic crystals in the infrared spectral range, as it allows the synthesis of large scale arrays of uniform structures with arbitrary geometries and arrangements. However, all-dielectric photonic crystals that provide birefringent optical responses in the infrared spectral range have not yet been demonstrated using direct laser writing techniques. Here we explore the form birefringence observed in photonic crystals composed of arrays of subwavelength-sized slanted polymer microwires. The photonic crystals investigated here were fabricated in a single fabrication step using direct

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13.10.2019
18:19 Technology.orgHow to make an Ornamental Lamp using Laser Cutting

Modern 3d printers can be used for much more than just 3d printing. By attaching a diode laser

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12.10.2019
15:45 RT.comLaser beams, an army of pacesetters & special Nike shoes: How Eliud Kipchoge ran the first sub 2-hour marathon

Kenya's Eliud Kipchoge carved out his own piece of history by becoming the first person to run a marathon in less than two hours in Vienna on Saturday, with every element of the run being scrutinized beforehand. Read Full Article at RT.com

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11.10.2019
05:17 Arxiv.org PhysicsLaser scanning reflection-matrix microscopy for label-free in vivo imaging of a mouse brain through an intact skull. (arXiv:1910.04681v1 [physics.bio-ph])

We present a laser scanning reflection-matrix microscopy combining the scanning of laser focus and the wide-field mapping of the electric field of the backscattered waves for eliminating higher-order aberrations even in the presence of strong multiple light scattering noise. Unlike conventional confocal laser scanning microscopy, we record the amplitude and phase maps of reflected waves from the sample not only at the confocal pinhole, but also at other non-confocal points. These additional measurements lead us to constructing a time-resolved reflection matrix, with which the sample-induced aberrations for the illumination and detection pathways are separately identified and corrected. We realized in vivo reflectance imaging of myelinated axons through an intact skull of a living mouse with the spatial resolution close to the ideal diffraction limit. Furthermore, we demonstrated

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05:17 Arxiv.org PhysicsImproved phase locking of laser arrays with nonlinear coupling. (arXiv:1910.04430v1 [physics.optics])

An arrangement based on a degenerate cavity laser for forming an array of non-linearly coupled lasers with an intra-cavity saturable absorber is presented. More than $30$ lasers were spatially phase locked and temporally Q-switched. The arrangement with nonlinear coupling was found to be $25$ times more sensitive to loss differences and converged $5$ times faster to the lowest loss phase locked state than with linear coupling, thus providing a unique solution to problems that have several near-degenerate solutions.

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10.10.2019
18:43 Nanowerk.comElectrochemistry to benefit photonics: nanotubes can control laser pulses

An international team of scientists has shown that the nonlinear optical response of carbon nanotubes can be controlled by electrochemical gating. This approach enables designing a device for controlling the laser pulse duration.

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16:19 Phys.orgElectrochemistry to benefit photonics: nanotubes can control laser pulses

An international team of scientists led by researchers from the Laboratory of Nanomaterials at the Skoltech Center for Photonics and Quantum Materials (CPQM) has shown that the nonlinear optical response of carbon nanotubes can be controlled by electrochemical gating. This approach enabled designing a device for controlling the laser pulse duration. The results of the study were published in the prestigious international journal Nano Letters.

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09.10.2019
10:44 Arxiv.org PhysicsFar-field Compound Super-resolution Lens for direct laser writing of arbitrary nano patterns and beyond. (arXiv:1910.03454v1 [physics.optics])

A low-cost compound super-resolution lens, consisting of a Plano-Convex lens and a Microsphere lens (PCM), was proposed and demonstrated for subwavelength direct laser scanning writing application. The PCM lens can achieve a far-field super-resolution of ~{\lambda}/3.5 in air (~6 um away from lens) which surpasses resolution limit of existing commercial objective lenses and is the first of its kind. Arbitrary nano-patterns can now be directly fabricated on various substrates in a simpleand low-cost manner using developed PCM lens. The lens can also be used for other applications including nano-imaging and sensing as well in a confocal configuration. This work may lead to the development of next-generation low-cost direct laser nanofabrication machine and superresolution imaging nanoscope.

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10:44 Arxiv.org PhysicsLongitudinal optical force of laser pulses in continuous media. (arXiv:1910.03183v1 [physics.optics])

From long time transverse and longitudinal optical forces are used for non-contact and noninvasive manipulation of small particle. The following question arises: What is the impact of these forces on the continuous media as air and silica. In this work we obtain analytical expressions for radiation force and radiation potential in dipole approximation of laser pulses propagating in dielectric media. The longitudinal force is proportional to the second time derivative of the intensity profile. At fixed initial energy of a laser pulse, as shorter is the pulse as bigger is the force. It is possible the neutral particles in gases solids be confined in the pulse envelope and to move with group velocity. In silica the longitudinal force of a femtosecond pulse is of few order of magnitude greater than molecular forces. Thus, the ablation in silica can be realized through broken molecular

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10:44 Arxiv.org PhysicsA fiber-based beam profiler for high-power laser beams in confined spaces and ultra-high vacuum. (arXiv:1910.03086v1 [physics.ins-det])

Laser beam profilometry is an important scientific task with well-established solutions for beams propagating in air. It has, however, remained an open challenge to measure beam profiles of high-power lasers in ultra-high vacuum and in tightly confined spaces. Here we present a novel scheme that uses a single multi-mode fiber to scatter light and guide it to a detector. The method competes well with commercial systems in position resolution, can reach through apertures smaller than $500\times 500~\mu m^2$ and is compatible with ultra-high vacuum conditions. The scheme is simple, compact, reliable and can withstand laser intensities beyond 2 MW/cm$^2$.

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10:44 Arxiv.org PhysicsRobust kHz-linewidth distributed Bragg reflector laser with optoelectronic feedback. (arXiv:1910.03041v1 [physics.optics])

We demonstrate a combination of optical and electronic feedback that significantly narrows the linewidth of distributed Bragg reflector lasers (DBRs). We use optical feedback from a long external fiber path to reduce the high-frequency noise of the laser. An electro-optic modulator placed inside the optical feedback path allows us to apply electronic feedback to the laser frequency with very large bandwidth, enabling robust and stable locking to a reference cavity that suppresses low-frequency components of laser noise. The combination of optical and electronic feedback allows us to significantly lower the frequency noise power spectral density of the laser across all frequencies and narrow its linewidth from a free-running value of 1.1 MHz to a stabilized value of 1.9 kHz, limited by the detection system resolution. This approach enables the construction of robust lasers with sub-kHz

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08.10.2019
06:21 Arxiv.org PhysicsDrop fragmentation by laser-pulse impact. (arXiv:1910.02522v1 [physics.flu-dyn])

We study the fragmentation of a liquid drop that is hit by a laser pulse. The drop expands into a thin sheet that breaks by the radial expulsion of ligaments from its rim and the nucleation and growth of holes on the sheet. By combining experimental data from two liquid systems with vastly different time- and length scales we show how the early-time laser-matter interaction affects the late-time fragmentation. We identify two Rayleigh--Taylor instabilities of different origins as the prime cause of the fragmentation and derive scaling laws for the characteristic breakup time and wavenumber. The final web of ligaments results from a subtle interplay between these instabilities and deterministic modulations of the local sheet thickness, which originate from the drop deformation dynamics and spatial variations in the laser-beam profile.

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06:21 Arxiv.org PhysicsEnergy gain by laser-accelerated electrons in a strong magnetic field. (arXiv:1910.02196v1 [physics.plasm-ph])

The manuscript deals with electron acceleration by a laser pulse in a plasma with a static uniform magnetic field $B_*$. The laser pulse propagates perpendicular to the magnetic field lines with the polarization chosen such that $({\bf{E}}_{laser} \cdot {\bf{B}}_*) = 0$. The focus of the work is on the electrons with an appreciable initial transverse momentum that are unable to gain significant energy from the laser in the absence of the magnetic field due to strong dephasing. It is shown that the magnetic field can initiate an energy increase by rotating such an electron, so that its momentum becomes directed forward. The energy gain continues well beyond this turning point where the dephasing drops to a very small value. In contrast to the case of purely vacuum acceleration, the electron experiences a rapid energy increases with the analytically derived maximum energy gain dependent on the

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06:21 Arxiv.org PhysicsObservation of Electric-Dipole Transitions in the Laser-Cooling Candidate Th$^-$. (arXiv:1910.02188v1 [physics.atom-ph])

Despite the fact that the laser cooling method is a well-established technique to obtain ultra-cold neutral atoms and atomic cations, it has so far never been applied to atomic anions due to the lack of suitable electric-dipole transitions. Efforts of more than a decade currently has La$^-$ as the only promising candidate for laser cooling. Our previous work showed that Th$^-$ is also a potential candidate. Here we report on a combination of experimental and theoretical studies to determine the relevant transition frequencies, transition rates, and branching ratios in Th$^-$. The resonant frequency of the laser cooling transition is determined to be $\nu/c$ = 4118.0 (10) cm$^{-1}$. The transition rate is calculated as A=1.17x10^4 s$^{-1}$. The branching fraction to dark states is very small, 1.47x10$^{-10}$, thus this represents an ideal closed cycle for laser cooling. Since Th has zero

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06:21 Arxiv.org PhysicsSolid-state laser refrigeration of a semiconductor optomechanical resonator. (arXiv:1910.02153v1 [physics.app-ph])

Photothermal heating represents a major constraint that limits the performance of many nanoscale optoelectronic and optomechanical devices including nanolasers, quantum optomechanical resonators, and integrated photonic circuits. Although radiation-pressure damping has been reported to cool an individual vibrational mode of an optomechanical resonator to its quantum ground state, to date the internal material temperature within an optomechanical resonator has not been reported to cool via laser excitation. Here we demonstrate the direct laser refrigeration of a semiconductor optomechanical resonator >20K below room temperature based on the emission of upconverted, anti-Stokes photoluminescence of trivalent ytterbium ions doped within a yttrium-lithium-fluoride (YLF) host crystal. Optically-refrigerating the lattice of a dielectric resonator has the potential to impact several fields

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07.10.2019
09:49 Technology.orgTiny, biocompatible laser could function inside living tissues

Researchers have developed a tiny nanolaser that can function inside living tissues without harming them. Just 50 to

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