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# Laser

23.06.2022
05:43 Laser cooling a membrane-in-the-middle system close to the quantum ground state from room temperature. (arXiv:2206.11169v1 [quant-ph])

Many protocols in quantum science and technology require initializing a system in a defined, pure quantum state. In the context of the motional state of massive resonators, this enables studying fundamental physics at the elusive quantum-classical transition, and measuring force and acceleration with enhanced sensitivity. Laser cooling has been a method of choice to prepare mechanical resonators in the quantum ground state, one of the simplest pure states. However, in order to overcome the heating and decoherence by the thermal bath, this usually has to be combined with cryogenic cooling. Here, we laser-cool an ultracoherent, soft-clamped mechanical resonator close to the quantum ground state directly from room temperature. To this end, we implement the versatile membrane-in-the-middle setup with one fiber mirror and one phononic crystal mirror, which reaches a quantum cooperativity close to unity already at room temperature. We furthermore introduce a powerful combination of coherent

05:43 Artificial optoelectronic spiking neuron based on a resonant tunnelling diode coupled to a vertical cavity surface emitting laser. (arXiv:2206.11044v1 [cs.ET])

Excitable optoelectronic devices represent one of the key building blocks for implementation of artificial spiking neurons in neuromorphic (brain-inspired) photonic systems. This work introduces and experimentally investigates an opto-electro-optical (O/E/O) artificial neuron built with a resonant tunnelling diode (RTD) coupled to a photodetector as a receiver and a vertical cavity surface emitting laser as a the transmitter. We demonstrate a well defined excitability threshold, above which this neuron produces 100 ns optical spiking responses with characteristic neural-like refractory period. We utilise its fan-in capability to perform in-device coincidence detection (logical AND) and exclusive logical OR (XOR) tasks. These results provide first experimental validation of deterministic triggering and tasks in an RTD-based spiking optoelectronic neuron with both input and output optical (I/O) terminals. Furthermore, we also investigate in theory the prospects of the proposed system for

05:43 Wavelength dependence of laser-induced excitation dynamics in silicon. (arXiv:2206.10817v1 [physics.optics])

Effect of laser wavelength on the carrier-phonon dynamics and damage threshold of silicon is studied numerically. Laser excitation dynamics in silicon is studied using Three-Temperature Model (3TM). We consider the evolution of electron, hole, and lattice temperatures separately and including band-gap re-normalization effect on optical properties of silicon. Finite Difference Time Domain method is used to model the laser field. Damage threshold calculated using the 3TM is in reasonable agreement with the experiments. Our results indicate that the competition of inter-band excitation, plasma heating, and electron-phonon relaxation process defines the damage threshold for various wavelengths and pulse durations.

05:42 Artificial optoelectronic spiking neuron based on a resonant tunnelling diode coupled to a vertical cavity surface emitting laser. (arXiv:2206.11044v1 [cs.ET])

Excitable optoelectronic devices represent one of the key building blocks for implementation of artificial spiking neurons in neuromorphic (brain-inspired) photonic systems. This work introduces and experimentally investigates an opto-electro-optical (O/E/O) artificial neuron built with a resonant tunnelling diode (RTD) coupled to a photodetector as a receiver and a vertical cavity surface emitting laser as a the transmitter. We demonstrate a well defined excitability threshold, above which this neuron produces 100 ns optical spiking responses with characteristic neural-like refractory period. We utilise its fan-in capability to perform in-device coincidence detection (logical AND) and exclusive logical OR (XOR) tasks. These results provide first experimental validation of deterministic triggering and tasks in an RTD-based spiking optoelectronic neuron with both input and output optical (I/O) terminals. Furthermore, we also investigate in theory the prospects of the proposed system for

22.06.2022
08:23 A single liquid chromatography procedure to concentrate, separate and collect size-selected polyynes produced by pulsed laser ablation in water. (arXiv:2206.10325v1 [physics.chem-ph])

Polyynes are linear carbon chains characterized by alternated single and triple bonds and terminated by hydrogen or other terminal substituents. They can be synthesized by pulsed laser ablation in liquid (PLAL) as a scalable, cost-effective, and fast physical technique. Water can be employed as a solvent for PLAL to avoid toxicity problems and to reduce costs compared to organic solvents. However, in this case, the production yield of polyynes reached is extremely low and prevents further characterization and implementation in new functional materials. In this work, we synthesized polyynes by pulsed laser ablation in water and we optimized the process parameters to improve the yield of polyynes by PLAL. Then, we developed a procedure entirely based on reversed-phase high-performance liquid chromatography (RP-HPLC) which effectively enables the concentration, separation and collection of polyynes according to their length. Since the polyynes sample is an aqueous solution, we could

08:23 A low-cost and reliable laser shutter interlock using a software-command interface. (arXiv:2206.09858v1 [physics.ins-det])

A simple and low-cost laser interlock is presented that operates via software commands issued by an ESP32 microcontroller. The architecture of the device is constructed to ensure the laser output is shut off in the event of either an open circuit on the interlock signal line from the laser enclosure or loss of power to the device. Unintentional exposure to the laser beam is prevented by overruling local controls (such as a keypad), until both the enclosure is re-interlocked and the user actively intervenes. The device presented is designed to close the mechanical shutter of a Spectra-Physics Millennia Pro pump laser while it continues to operate internally. The hardware and coding are versatile enough to be deployed on any instrument that receives software commands via a serial interface.

08:23 Absolute frequencies of H13C14N hydrogen cyanide hyper-fine transitions in 1,5 {\mu}m region with saturated spectroscopy and sub-kHz scanning laser. (arXiv:2206.09232v1 [physics.optics])

The wide span and high density of lines in its rovibrational spectrum render the hydrogen cyanide a useful spectroscopic media for referencing absolute frequencies of lasers in optical communication and dimensional metrology.We were first to determine the molecular transitions' center frequencies of the H13C14N isotope in the range from 1526 nm to 1566 nm with 1,3 * 10^{-10} fractional uncertainty. We investigated the molecular transitions with a highly coherent and widely tunable scanning laser that was precisely referenced to a Hydrogen maser through an optical frequency comb. We demonstrated an approach to stabilize the operational conditions needed to maintain constantly low pressure of the hydrogen cyanide to carry out the saturated spectroscopy with the third-harmonic synchronous demodulation. Compared to the previous result, we demonstrated approximately a fourtyfold improvement in the line centers' resolution.

08:23 Sub-recoil clock-transition laser cooling enabling shallow optical lattice clocks. (arXiv:2206.09056v1 [physics.atom-ph])

Laser cooling is a key ingredient for quantum control of atomic systems in a variety of settings. In divalent atoms, two-stage Doppler cooling is typically used to bring atoms to the uK regime. Here, we implement a pulsed radial cooling scheme using the ultranarrow 1S0-3P0 clock transition in ytterbium to realize sub-recoil temperatures, down to tens of nK. Together with sideband cooling along the one-dimensional lattice axis, we efficiently prepare atoms in shallow lattices at an energy of 6 lattice recoils. Under these conditions key limits on lattice clock accuracy and instability are reduced, opening the door to dramatic improvements. Furthermore, tunneling shifts in the shallow lattice do not compromise clock accuracy at the 10-19 level.

08:23 Radiation pressure acceleration of high-quality ion beams using ultrashort laser pulses. (arXiv:2206.09007v1 [physics.plasm-ph])

The generation of compact, high-energy ion beams is one of the most promising applications of intense laser-matter interactions, but the control of the beam spectral quality remains an outstanding challenge. We show that in radiation pressure acceleration of a thin solid target the onset of electron heating is determined by the growth of the Rayleigh-Taylor-like instability at the front surface and must be controlled to produce ion beams with high spectral quality in the light sail regime. The growth rate of the instability imposes an upper limit on the laser pulse duration and intensity to achieve high spectral beam quality and we demonstrate that under this optimal regime, the maximum peak ion beam energy per nucleon is independent of target density, composition, and laser energy (transverse spot size). Our predictions are validated by two- and three-dimensional particle-in-cell simulations, which indicate that for recent and upcoming experimental facilities using ultrashort

20.06.2022
06:43 Laser-induced electron dynamics and surface modification in ruthenium thin films. (arXiv:2206.08690v1 [cond-mat.mtrl-sci])

We performed the experimental and theoretical study of the heating and damaging of ruthenium thin films induced by femtosecond laser irradiation. Results of an optical pump-probe thermoreflectance experiment with rotating sample allowing to significantly reduce heat accumulation in irradiated spot are presented. We show the evolution of surface morphology from growth of a heat-induced oxide layer at low and intermediate laser fluences to cracking and grooving at high fluences. Theoretical analysis of pump-probe signal allows us to relate behavior of hot electrons in ruthenium to the Fermi smearing mechanism. The analysis of heating is performed with the two-temperature modeling and molecular dynamics simulation, results of which demonstrate that the calculated melting threshold is higher than experimental damage threshold. We attribute it to heat-induced surface stresses leading to cracking which accumulates to more severe damage morphology. Our results provide an upper limit for

06:43 The impact of the substrate on the opto-thermal response of thin metallic targets following irradiation with femtosecond laser pulses. (arXiv:2206.08577v1 [physics.optics])

Femtosecond pulsed lasers have been widely used over the past decades due to their capability to fabricate precise patterns at the micro- and nano- lengths scales. A key issue for efficient material processing is the determination of the laser parameters used in the experimental set ups. Despite a systematic investigation that has been performed to highlight the impact of every parameter independently, little attention has been drawn on the role of the substrate material on which the irradiated solid is placed. In this work, the influence of the substrate is emphasised for films of various thicknesses which demonstrates that both the optical and thermophysical properties of the substrate affect the thermal fingerprint on the irradiated film while the impact is manifested to be higher at smaller film sizes. Two representative materials, silicon and fused silica have been selected as typical substrates for thin films of different optical and thermophysical behaviour (gold and nickel) and

06:43 Machine Learning-Driven Process of Alumina Ceramics Laser Machining. (arXiv:2206.08747v1 [cs.CE])

Laser machining is a highly flexible non-contact manufacturing technique that has been employed widely across academia and industry. Due to nonlinear interactions between light and matter, simulation methods are extremely crucial, as they help enhance the machining quality by offering comprehension of the inter-relationships between the laser processing parameters. On the other hand, experimental processing parameter optimization recommends a systematic, and consequently time-consuming, investigation over the available processing parameter space. An intelligent strategy is to employ machine learning (ML) techniques to capture the relationship between picosecond laser machining parameters for finding proper parameter combinations to create the desired cuts on industrial-grade alumina ceramic with deep, smooth and defect-free patterns. Laser parameters such as beam amplitude and frequency, scanner passing speed and the number of passes over the surface, as well as the vertical distance

17.06.2022
07:52 Intrinsic Spectrum Analysis of Laser Dynamics Based on Fractional Fourier Transform. (arXiv:2206.08059v1 [physics.optics])

Intrinsic spectrum that results from the coupling of spontaneous emission in a laser cavity, can determine the energy concentration and coherence of lasers, which is crucial for the optical high-precision measurement. Up to now, it is hard to analyze the intrinsic spectrum in the high-speed laser dynamics process, especially under the condition of fast wavelength sweeping. In this work, a new method to analyze the laser intrinsic spectrum is proposed with the laser energy decomposition to a series of chirp-frequency signals, which is realized by fractional Fourier transform (FRFT) of the coherently reconstructed laser waveform. The new understanding of the energy distribution of lasers contributes to the accurate characterization of laser dynamical parameters in time-frequency domain. In the proof-of-concept experiment, the time-frequency dynamical process of a commercial wavelength swept laser is tested with different wavelength-scanning speeds, and the most suitable measurement time

07:52 Laser-Induced Fluorescence Spectroscopy (LIFS) of Trapped Molecular Ions in Gas-phase. (arXiv:2206.08034v1 [quant-ph])

This review presents the Laser-Induced Fluorescence Spectroscopy (LIFS) of trapped gas-phase molecular ions. A brief description of the theory and experimental approaches involved in fluorescence spectroscopy, together with state-of-the-art LIFS experiments employing ion traps, is presented. Quadrupole ion traps are commonly used for spatial confinement of ions. One of the main challenges involved in such experiments is poor Signal-to-Noise Ratio (SNR) arising due to weak gas-phase fluorescence emission, high background noise, and small solid angle for the fluorescence collection optics. The experimental approaches based on the integrated high-finesse optical cavities provide a better (typically an order of magnitude more) SNR in the detected fluorescence than the single-pass detection schemes. Another key to improving the SNR is to exploit the maximum solid angle of light collection by choosing high numerical aperture (NA) collection optics. The latter part of the review summarises

07:52 Direct ultrafast parametric amplification pumped by a picosecond thin-disk laser. (arXiv:2206.07929v1 [physics.optics])

Optical quadratic nonlinearity is ultrafast in nature, while parametric interaction usually manifests only the broadband characteristic. Enormous progress has been made toward broadband phase-matching for parametric amplification and wide applications. In existing devices of broadband parametric amplification, the power efficiency of conversion is restricted to approximately the energy efficiency, and the desire for the signal power enhancement necessitates additional pulse compression after amplification. Here, we demonstrate ultrafast parametric amplification having an extraordinary power efficiency of 1155%; this allows the generation of intense femtosecond pulses without the need for a pulse stretcher and compressor. Direct femtosecond signal amplification by picosecond pumping is enabled by an ultrafast parametric environment in which the pre-delayed signal of faster speed gradually overtakes and effectively depletes the pump of slower speed as they propagate in a nonlinear

16.06.2022
23:53 The AGM Glory G1S phone boasts an infrared camera and laser pointer

Jack Wallen kicks the tires of the AGM Glory G1S Android phone -- and comes away seriously impressed by this built-like-a-tank phone with some rather unique features.

10:32 Intensity correlations in quantum cascade laser harmonic frequency combs. (arXiv:2206.07624v1 [physics.optics])

A novel study on harmonic frequency combs emitted by Quantum Cascade Lasers (QCLs) is here presented, demonstrating the presence of intensity correlations between twin modes characterising the emission spectra. These originate from a Four-Wave Mixing (FWM) process driven by the active medium's third-order non-linearity. The study of such correlations is essential for the engineering of a new generation of semiconductor devices with the potential of becoming integrated emitters of light with quantum properties, such as squeezing and entanglement. Starting from experimental results, the limits of state-of-the-art technology are discussed as well as the possible methodologies that could lead to the detection of non-classical phenomena, or alternatively improve the design of QCLs, in the compelling perspective of generating quantum correlations in mid-infrared light.

10:32 Efficient and compact source of tuneable ultrafast deep ultraviolet laser pulses at 50 kHz repetition rate. (arXiv:2206.07103v1 [physics.optics])

We demonstrate a bright, efficient, and compact source of tuneable deep ultraviolet ultrafast laser pulses based on resonant dispersive wave emission in hollow capillary fibre. In a total footprint of only 120 cm $\times$ 75 cm, including the Yb-based drive laser, we generate pulses between 208 nm and 363 nm at 50 kHz repetition rate with a total efficiency of up to 3.6%

05:42 New thulium fiber laser system may provide improved outcomes in pediatric patients with urinary stones

A new thulium fiber laser system may provide improved outcomes in the treatment of urinary stones for pediatric patients, compared to the current standard for laser lithotripsy, reports a study in The Journal of Urology, an Official Journal of the American Urological Association (AUA). The journal is published in the Lippincott portfolio by Wolters Kluwer.

15.06.2022
18:03 Physicists make leaps in reading out qubits with laser light

Qubits are a basic building block for quantum computers, but they're also notoriously fragile—tricky to observe without erasing their information in the process. Now, new research from the University of Colorado Boulder and the National Institute of Standards and Technology (NIST) could be a leap forward for handling qubits with a light touch.

06:03 Mode-coupling effects in an optically-injected dual-wavelength laser. (arXiv:2206.06721v1 [physics.optics])

Lasers designed to emit at multiple and controllable modes, or multi-wavelength lasers, have the potential to become key building blocks for future microwave photonic technologies. While many interesting schemes relying on optical injection have been proposed, the nonlinear mode coupling between different modes of a multi-wavelength laser and their dynamical behavior under optical injection remains vastly unexplored. Here, we experimentally and numerically study the effect of optical injection around the suppressed mode of a dual12 wavelength laser and the resulting interactions with the dominant mode. We highlight a wavelength shift of the dominant mode triggered by injection locking of the suppressed mode and report a strong impact of the mode suppression ratio on the locking range. Finally, we show numerically that the cross-coupling parameter between the two modes might have a key role in this effect.

14.06.2022
17:33 Physicists build an atom laser that can stay on forever

Lasers use coherent waves of light: All the light inside a laser vibrates completely in sync. Meanwhile, quantum mechanics tells us that particles like atoms should also be thought of as waves. As a result, we can build "atom lasers" containing coherent waves of matter. But can we make these matter waves last, so that they may be used in applications? In research that was published in Nature this week, a team of Amsterdam physicists shows that the answer to this question is affirmative.

08:43 Polarization dependent beam pointing jitter in laser wake field accelerators. (arXiv:2206.06133v1 [physics.acc-ph])

We present experimental results, which show a laser polarization dependent contribution to electron beam pointing jitter in laser wakefield accelerators (LWFA). We develop a theoretical model for the polarization dependence in terms of the transverse dynamics of trapped electrons, resonantly driven by bubble centroid oscillations. The latter are generated by the carrier wave phase evolution at the self-steepened laser pulse front. In the model, the polarization dependent jitter originates from shot-to-shot fluctuations of the laser carrier envelope phase. The model is verified by particle in cell simulations and suggests that for non-CEP stabilized systems the polarization dependent jitter may form an ultimate limit to beam pointing stability in LWFAs.

08:43 Localized absorption of laser energy in X-mode configuration of magnetized plasma. (arXiv:2206.05470v1 [physics.plasm-ph])

The heating of ions via lower hybrid waves has been observed in several astrophysical as well as laboratory plasmas. We have conducted Particle-In-Cell simulations to demonstrate absorption of the incident laser pulse at a chosen localized point in the target by manipulating the plasma density profile. We show that a part of the incident laser propagates inside plasma target, when its frequency lies below the lower hybrid resonance frequency. Thereafter, as it experiences a negative density gradient, it approaches the resonance point where its group velocity approaches zero. This is where the electromagnetic energy prominently gets converted into electrostatic and eventually into kinetic energy of ions. Thus by tailoring the plasma density profile one can have the absorption of incident electromagnetic wave energy at a designated location inside the plasma. This may have importance in various applications where energy deposition/heating of plasma at a localized region is desirable.

08:43 Laser cooling assisted thermal management of lightsails. (arXiv:2206.05383v1 [physics.optics])

A lightsail can be accelerated to ultra-high speed by the radiation pressure of a laser having an intensity of the order of GW/m$^2$, which though presents a critical challenge in the thermal management of lightsails. In this letter, we explore the applicable regimes of solid-state laser cooling in dissipating heat in additional to the previously explored radiative cooling approach. We begin by examining the cooling capacity of laser cooling, and show that the cooling rate from a micron-thick layer doped with ytterbium ions can exceed that of blackbody thermal emission. This allows more intense laser illumination upon material damage, and consequently shortened acceleration distance. Next, we explore the impact of the limited operating bandwidth of laser cooling to account for the Doppler shift of the pumping laser, and conclude that laser cooling is helpful for target velocities $\lesssim5\%$ for room-temperature operations.

08:42 Imagination-augmented Navigation Based on 2D Laser Sensor Observations. (arXiv:2206.05775v1 [cs.RO])

Autonomous navigation of mobile robots is an essential task for various industries. Sensor data is crucial to ensure safe and reliable navigation. However, sensor observations are often limited by different factors. Imagination can assist to enhance the view and aid navigation in dangerous or unknown situations where only limited sensor observation is available. In this paper, we propose an imagination-enhanced navigation based on 2D semantic laser scan data. The system contains an imagination module, which can predict the entire occupied area of the object. The imagination module is trained in a supervised manner using a collected training dataset from a 2D simulator. Four different imagination models are trained, and the imagination results are evaluated. Subsequently, the imagination results are integrated into the local and global cost map to benefit the navigation procedure. The approach is validated on three different test maps, with seven different paths for each map. The

13.06.2022
19:23 Physicists build an atom laser that can stay on forever

A team of physicists has managed to solve the difficult problem of creating a continuous Bose-Einstein Condensate.

10.06.2022
16:32 Magnetizing laser-driven inertial fusion implosions

Nuclear fusion is a widely studied process through which atomic nuclei of a low atomic number fuse together to form a heavier nucleus, while releasing a large amount of energy. Nuclear fusion reactions can be produced using a method known as inertial confinement fusion, which entails the use of powerful lasers to implode a fuel capsule and produce plasma.

09.06.2022
14:23 Palaeontologist reveals a dinosaur belly button using laser imaging

Paleontologists have set a new record for the oldest belly button ever found in reptiles and mammals, after scientists from The Chinese University of Hong Kong (CUHK) and from around the world used a high-tech laser imaging technology to finally reveal the finest details of a 125-million-year old dinosaur fossil found in China 20 years ago.

08.06.2022
10:42 Semiconductor ring laser frequency combs with active directional couplers. (arXiv:2206.03379v1 [physics.optics])

Rapid development of Fabry-Perot quantum cascade laser frequency combs has converted them from laboratory devices to key components of next-generation fast molecular spectrometers. Recently, free-running ring quantum cascade lasers allowed generation of new frequency comb states induced by phase turbulence. In absence of efficient light outcoupling, ring quantum cascade lasers are not suited for applications as they are limited in their power output to microwatt levels. Here we demonstrate electrically pumped ring quantum cascade lasers with integrated active directional couplers. These devices generate self-starting frequency combs and have output power above ten milliwatts at room temperature. We study the transmission of the ring-waveguide resonator system below the lasing threshold, which reveals the ability to individually control the mode indices in the coupled resonators, their quality factors, and the coupling coefficient. When the ring resonator is pumped above the lasing

10:42 Generation of extreme ultraviolet laser by single-photon process. (arXiv:2206.03119v1 [physics.optics])

To generate laser with short wavelength is a bottle-neck problem in laser technology. The extreme ultraviolet (EUV) lasers are usually produced with low efficiency by nonlinear multi-photon process. Here we show the generation of 58.4 nm laser by a single-photon-excitation related stimulated anti-Stokes Raman scattering (ASRS) with an efficiency higher than that of high harmonic generation (HHG). Utilizing microwave excited helium in the metastable 1s2s state irradiated by a resonant femto-second 2058 nm laser, we obtain pulsed 58.4 nm laser with a divergence of 1.9 mrad, suggesting its coherent character. The pulse decay time of 426 ps shorter than the lifetime of spontaneous emission also shows its stimulated property. Our results show an applicable path towards up-conversion by single-photon process to generate intense laser with wavelength shorter than 58.4 nm.

10:42 Effects of Laser-Annealing on Fixed-Frequency Superconducting Qubits. (arXiv:2206.03099v1 [quant-ph])

As superconducting quantum processors increase in complexity, techniques to overcome constraints on frequency crowding are needed. The recently developed method of laser-annealing provides an effective post-fabrication method to adjust the frequency of superconducting qubits. Here, we present an automated laser-annealing apparatus based on conventional microscopy components and demonstrate preservation of highly coherent transmons. In one case, we observe a two-fold increase in coherence after laser-annealing and perform noise spectroscopy on this qubit to investigate the change in defect features, in particular two-level system defects. Finally, we present a local heating model as well as demonstrate aging stability for laser-annealing on the wafer scale. Our work constitutes an important first step towards both understanding the underlying physical mechanism and scaling up laser-annealing of superconducting qubits.

07.06.2022
06:13 Mapping the direction of electron ionization to phase delay between VUV and IR laser pulses. (arXiv:2206.02595v1 [physics.atom-ph])

We theoretically demonstrate a one-to-one mapping between the direction of electron ionization and the phase delay between a linearly polarized VUV and a circular IR laser pulse. To achieve this, we use an ultrashort VUV pulse that defines the moment in time and space when an above threshold electron is released in the IR pulse. The electron can then be accelerated to high velocities escaping in a direction completely determined by the phase delay between the two pulses. The dipole matrix element to transition from an initial bound state of the N$_2$ molecule, considered in this work, to the continuum is obtained using quantum mechanical techniques that involve computing accurate continuum molecular states. Following release of the electron in the IR pulse, we evolve classical trajectories, neglecting the Coulomb potential and accounting for quantum interference, to compute the distribution of the direction and magnitude of the final electron momentum. The concept we theoretically

06:13 Laser-induced crystallization of copper oxide thin films: A comparison made between Gaussian and chevron-beam profiles provides a clue for the failure of Gaussian-beam profile. (arXiv:2206.02532v1 [physics.app-ph])

The use of laser with a Gaussian-beam profile is frequently adopted in attempts of crystallizing non-single-crystal thin films; however, it merely results in the formation of poly-crystal thin films. In this paper, selective area crystallization of non-single-crystal copper(II) oxide (CuO) is described. The crystallization is induced by laser, laser-induced crystallization, with a beam profile in the shape of chevron. The crystallization is verified by the exhibition of a transition from a non-single-crystal phase consisting of small 100 nm x 100 nm grains of CuO to a single-crystal phase of copper(I) oxide (Cu2O). The transition is identified by electron back scattering diffraction and Raman spectroscopy, which clearly suggests that a single-crystal domain of Cu2O with size as large as 5 {\mu}m x 1 mm develops. Provided these experimental findings, a theoretical assessment based on a cellular automaton model, with the behaviors of localized recrystallization and stochastic nucleation,

06:13 Powerful laser-produced quasi-half-cycle THz pulses. (arXiv:2206.02464v1 [physics.plasm-ph])

The Maxwell equations based 3D analytical solution for the terahertz half-cycle electromagnetic wave transition radiation pulse has been found. This solution describes generation and propagation of transition radiation into free space from laser-produced relativistic electron bunch crossing a target-vacuum interface as a result of ultrashort laser pulse interaction with a thin high-conductivity target. The analytical solution found complements the theory of laser initiated transition radiation by describing the generated THz wave shape at the arbitrary distance from the generating target surface domain including near-field zone rather than the standard far-field characterization. The analytical research has also been supplemented with the 3D simulations using the finite-diference time-domain (FDTD) method, which makes it possible for description of much wider spatial domain as compared to that from the particle-in-cell (PIC) approach. The results reported fundamentally shed light on

06:13 Performance of TPC detector prototype integrated with UV laser tracks for the circular collider. (arXiv:2206.02375v1 [physics.ins-det])

Several new experimental concepts in high-energy particle physics have been proposed in recent years. The physical goals include precisely measuring the properties of particles such as Higgs, Z and W, and even looking for signs of new physics at future colliders. To meet the evolving requirements for particle track detector, Time Projection Chamber(TPC) detector prototype integrated with a UV laser track system was developed for the main track detector at Circular Electron Positron Collider(CEPC). This prototype consists of 6 horizontal laser tracks around TPC detector chamber, a fast electronics readout of 1280 channels, a GEM detector with $200\times 200\,mm^2$ active area, and the DAQ system. The hit resolution, dE/dx resolution and drift velocity were studied by measuring and analyzing using the TPC prototype and UV laser tracks. The dE/dx resolution of the prototype was measured to be $(8.9\pm0.4)\,\%$. Extrapolating this to CEPC TPC with 220 layers and longer track, the

06:13 The synergy of electromagnetic effects and thermophysical properties of metals in the formation of laser induced periodic surface structures. (arXiv:2206.02351v1 [physics.optics])

Femtosecond pulsed lasers have been widely used over the past decades for precise materials structuring at the micro- and nano- scales. In order, though, to realize efficient material processing and account for the formation of laser induced periodic surfaces structures (LIPSS), it is very important to understand the fundamental laser-matter interaction processes. A significant contribution to the LIPSS profile appears to originate from the electromagnetic fingerprint of the laser source. In this work, we follow a systematic approach to predict the pulse-by-pulse formation of LIPSS on metals due to the development of a spatially periodic energy deposition that results from the interference of electromagnetic far fields on a non-flat surface profile. On the other hand, we demonstrate that the induced electromagnetic effects, alone, are not sufficient to allow the LIPSS formation, therefore, we emphasize on the crucial role of electron diffusion and electron-phonon coupling on the

06:13 High-repetition-rate seeded free-electron laser enhanced by the self-modulation. (arXiv:2206.02195v1 [physics.acc-ph])

Recently, the self-modulation scheme of a weakly pre-bunched electron beam has been proposed [Yan et al., Physical Review Letters 126, 084801 (2021)], which is of great promise for high-repetition-rate seeded free-electron lasers (FELs), such as high-gain harmonic generation (HGHG). In this paper, the self-modulation scheme is systematically analyzed and optimized, and further experiments in which the self-modulator is resonant at the second harmonic of the seed laser are conducted. The three-dimensional numerical simulations show that the required seed laser intensity in the self-modulation scheme is around three orders of magnitude lower than that of the standard HGHG through the optimization of the beam size or the peak current. More importantly, by reasonably setting the initial energy modulation and the resonance of the self-modulator, a more prominent bunching factor and lase at the 30th harmonic of the seed laser can be achieved in a single-stage HGHG. Moreover, the experiment

06.06.2022
09:12 Ultrafast laser pulse characterization by THG d-scan using optically enhanced graphene coatings. (arXiv:2206.01676v1 [physics.optics])

We have successfully functionalized 5 layers of TCVD-grown graphene by photoassisted transfer hydrogenation reaction with formic acid, in order to increase its nonlinear optical response and laser-induced damage resilience. Using the functionalized graphene samples, we were able to fully characterize sub-10 fs ultrashort laser pulses using THG dispersion-scan, with results that are in excellent agreement with the ones obtained with pristine graphene samples.

09:12 Pulsed laser ablation in liquid of sp-carbon chains: status and recent advances. (arXiv:2206.01238v1 [physics.chem-ph])

This review provides a discussion of the current state of research on sp-carbon chains synthesized by pulsed laser ablation in liquid. In recent years, pulsed laser ablation in liquid (PLAL) has been widely employed for polyynes synthesis thanks to its flexibility with varying laser parameters, solvents, and targets. This allows the control of sp-carbon chains properties as yield, length, termination and stability. Although many reviews related to PLAL have been published, a comprehensive work reporting the current status and advances related to the synthesis of sp-carbon chains by PLAL is still missing. Here we first review the principle of PLAL and the mechanisms of formation of sp-carbon chains. Then we discuss the role of laser fluence (i.e. energy density), solvent, and target for sp-carbon chains synthesis. Lastly, we report the progress related to the prolonged stability of sp-carbon chains by PLAL encapsulated in polymeric matrices. This review will be a helpful guide for

03.06.2022
10:03 Background-oriented Schlieren technique with vector tomography for measurement of axisymmetric pressure fields of laser-induced underwater shock waves. (arXiv:2206.00811v1 [physics.flu-dyn])

This study aims to overcome the problems that existing background-oriented schlieren (BOS) techniques based on computed tomography (CT-BOS) face when measuring pressure fields of laser-induced underwater shock waves. To do this, it proposes a novel BOS technique based on vector tomography (VT-BOS) of an axisymmetric target. The remarkable feature of the proposed technique is the reconstruction of an axisymmetric vector field with nonzero divergence, such as the field of a laser-induced underwater shock wave. This approach is based on an approximate relation between the projection of the axisymmetric vector field and the reconstructed vector field. For comparison, the pressure fields of underwater shock waves are measured with VT-BOS, CT-BOS, and a needle hydrophone. It is found that VT-BOS is significantly better than CT-BOS in terms of better convergence, less dependence on the spatial resolution of the acquired images, and lower computational cost. The proposed technique can be

10:03 Adversarial Laser Spot: Robust and Covert Physical Adversarial Attack to DNNs. (arXiv:2206.01034v1 [cs.CV])

02.06.2022
10:13 It’s a trap! Laser light ensnared by invisible bonds

In collaboration with the group of Professor Mordechai Segev (Technion, Israel Institute of Technology), physicists from the group

05:22 Design Study of a Dielectric Laser Undulator. (arXiv:2206.00593v1 [physics.acc-ph])

Dielectric laser acceleration (DLA) achieves remarkable gradients from the optical near fields of a grating structure. Tilting the dielectric grating with respect to the electron beam leads to deflection forces and the DLA structure can be utilized as a microchip undulator. We investigate the beam dynamics in such structures analytically and by numerical simulations. A crucial challenge is to keep the beam focused, especially in direction of the narrow channel. An alternating phase focusing scheme is optimized for this purpose and matched lattice functions are obtained. We distinguish synchronous operation with phase jumps in the grating and asynchronous operation with a strictly periodic grating and well-designed synchronicity mismatch. Especially the asynchronous DLA undulator is a promising approach, since a simple, commercially available grating suffices for the focusing lattice design. We pave the way towards experiments of radiation generation in these structures and provide

05:22 Stable and high quality electron beams from staged laser and plasma wakefield accelerators. (arXiv:2206.00507v1 [physics.acc-ph])

We present experimental results on a plasma wakefield accelerator (PWFA) driven by high-current electron beams from a laser wakefield accelerator (LWFA). In this staged setup stable and high quality (low divergence and low energy spread) electron beams are generated at an optically-generated hydrodynamic shock in the PWFA. The energy stability of the beams produced by that arrangement in the PWFA stage is comparable to both single-stage laser accelerators and plasma wakefield accelerators driven by conventional accelerators. Simulations support that the intrinsic insensitivity of PWFAs to driver energy fluctuations can be exploited to overcome stability limitations of state-of-the-art laser wakefield accelerators when adding a PWFA stage. Furthermore, we demonstrate the generation of electron bunches with energy spread and divergence superior to single-stage LW-FAs, resulting in bunches with dense phase space and an angular-spectral charge density beyond the initial drive beam

05:22 LUXE: A new experiment to study non-perturbative QED in $e^-$-laser and $\gamma$-laser collisions. (arXiv:2206.00403v1 [hep-ex])

The LUXE experiment (Laser Und XFEL Experiment) is a new experiment in planning at DESY Hamburg using the electron beam of the European XFEL. At LUXE, the aim is to study collisions between a high-intensity optical laser and up to $16.5\,$GeV electrons from the Eu.XFEL electron beam, or, alternatively, high-energy secondary photons. The physics objectives of LUXE are to measure processes of Quantum Electrodynamics (QED) at the strong-field frontier, where QED is non-perturbative. This manifests itself in the creation of physical electron-positron pairs from the QED vacuum. LUXE intends to measure the positron production rate in a new physics regime at an unprecedented laser intensity. Additionally, the high-intensity Compton photon beam of LUXE can be used to search for physics beyond the Standard Model.

05:22 Wavelength-division multiplexing communications using integrated soliton microcomb laser source. (arXiv:2206.00256v1 [physics.optics])

In this Letter, we investigate the feasibility and performance of wavelength division multiplexed (WDM) optical communications using an integrated dissipative Kerr soliton micro-comb as the multi-channel laser source. First, we confirm that soliton microcomb pumped directly by a DFB laser self-injection locked to the host micro-cavity has sufficiently low frequency and amplitude noises to encode advanced data formats. Second, perfect soliton crystals are exploited to boost the power level of each microcomb line, so that they can be directly used for data modulation excluding pre-amplification. Third, in a proof-of-concept experiment we demonstrate 7-channel 16-QAM data transmissions using an integrated perfect soliton microcomb as the laser carriers, excellent data receiving performances are obtained under various fiber link distances and amplifier configurations. Our study reveals that fully integrated Kerr soliton microcombs are viable and advantageous for optical data

01.06.2022
16:53 Using laser technology to measure the rotational cooling of molecular ions colliding with electrons

When it is free in cold space, a molecule will spontaneously cool down by slowing its rotation and losing rotational energy in quantum transitions. Physicists have shown that this rotational cooling process can be accelerated, slowed down and even inverted by the molecule's collisions with surrounding particles.

16:33 It's a trap! Laser light ensnared by invisible bonds

Scientists have demonstrated a novel type of mechanism that can prevent light waves from spreading freely. In their recent experiments, the physicists observed that such light localization is possible, demonstrating the uncanny sensitivity of wave propagation across a wide range of spatial length scales.

07:52 Enhanced energy deposition and carrier generation in silicon induced by two-color intense femtosecond laser pulses. (arXiv:2205.15625v1 [physics.plasm-ph])

We theoretically investigate the optical energy absorption of crystalline silicon subject to dual-color femtosecond laser pulses, using the time-dependent density functional theory (TDDFT). We employ the modified Becke-Johnson (mBJ) exchange-correlation potential which reproduces the experimental direct band gap energy $E_g$. We consider situations where the one color is in the ultraviolet (UV) range above $E_g$ and the other in the infrared (IR) range below it. The energy deposition is examined as a function of mixing ratio $\eta$ of the two colors with the total pulse energy conserved. Energy transfer from the laser pulse to the electronic system in silicon is dramatically enhanced by simultaneous dual-color irradiation and maximized at $\eta\sim 0.5$. Increased is the number of generated carriers, not the absorbed energy per carrier. The effect is more efficient for lower IR photon energy, or equivalently, larger vector-potential amplitude. As the underlying mechanism is identified

31.05.2022
16:13 Functional nonlinear optical nanoparticles synthesized by laser ablation

Nonlinear optics is an important research direction with various applications in laser manufacturing, nanostructures' fabrication, sensor design, optoelectronics, biophotonics, and quantum optics, etc. Nonlinear optical materials are the fundamental building blocks, which are critical for broad fields ranging from scientific research, industrial production, to military. After many years of development, nonlinear optics has become the pillars for various frontier research and widely used optical systems, including laser fabrication, optical imaging, information processing & communications, as well as nanoscale lithography. Advances in this topic can potentially boost many disciplines.

10:23 Laser-induced dynamic alignment of the HD molecule without the Born-Oppenheimer approximation. (arXiv:2205.15229v1 [physics.chem-ph])

We present a computational study of dynamic alignment of the HD molecule induced by a fast-varying laser field The Born-Oppenheimer (BO) approximation is not invoked and the only essential approximation, in addition to the electric-dipole approximation for the matter-field interaction, is the choice of time-independent explicitly correlated Gaussian basis functions. We use a variational, electric-field-dependent basis-set construction procedure, which is validated by comparing with virtually exact grid-based simulations for two one-dimensional model systems: laser-driven electron dynamics in a soft attractive Coulomb potential and nuclear rovibrational dynamics in a Morse potential. While well defined within the BO approximation, the concept of alignment is harder to define uniquely without it. For the HD molecule, however, we may construct an operator in terms of pseudo-proton coordinates that mimics the angular distributions observed experimentally by Coulomb-explosion techniques.

10:23 Perovskite quantum dot topological laser. (arXiv:2205.14932v1 [physics.optics])

Various topological laser concepts have recently enabled the demonstration of robust light-emitting devices that are immune to structural deformations and tolerant to fabrication imperfections. Current realizations of photonic cavities with topological boundaries are often limited by outcoupling issues or poor directionality and require complex design and fabrication that hinder operation at small wavelengths. Here we propose a topological cavity design based on interface states between two one-dimensional photonic crystals with distinct Zak phases and demonstrate a lithography-free, single-mode perovskite laser emitting in the green. Few monolayers of solution processed all-inorganic cesium lead halide perovskite quantum dots are used as ultrathin gain medium. The topological laser has planar design with large output aperture, akin to vertical-cavity surface-emitting lasers (VCSELs) and is robust against variations of the thickness of the gain medium, from deeply subwavelength to

10:23 Radium-containing molecular cations amenable for laser cooling. (arXiv:2205.14429v1 [physics.chem-ph])

Recently a new wave of interest to spectroscopy of radioactive compounds has raised due to successful applications of the new experimental ISOL/CRIS technique to optical spectroscopy of radium monofluoride molecules. This opens great prospects to searches of the effects connected with new physics'' which point on deviations of the physical laws from those established by Standard Model of elementary particles. Considerable advantages in experiments for search for such effects would be provided by the abilities to trap the working molecules, their laser-coolability and presence of co-magnitometer molecular states and also a variety of accessible nuclear isotopes of the elements in the molecule with different nuclear multipole moments. Laser-coolable polyatomic molecular ions containing Ra nuclei shall meet the above criteria and in the present article we are considering a number of prospective molecular ions and calculating their electronic structure and molecular properties.

10:23 Low-Drift-Rate External Cavity Diode Laser. (arXiv:2205.14149v1 [physics.ins-det])

We present the design, construction, and simulation of a simple, low-cost external cavity diode laser with a measured free-running frequency drift rate of 1.4(1)~MHz/h at 852 nm. This performance is achieved via a compact, nearly monolithic aluminum structure to minimize temperature gradients across the laser cavity. We present thermal finite element method simulations which quantify the effects of temperature gradients, and suggest that the drift rate is likely limited by laser-diode aging.

10:23 Liquid-cooled modular gas cell system for high-order harmonic generation using high average power laser systems. (arXiv:2205.14145v1 [physics.ins-det])

We present the design and implementation of a new, modular gas target suitable for high-order harmonic generation using high average power lasers. To ensure thermal stability in this high heat load environment, we implement an appropriate liquid cooling system. The system can be used in multiple-cell configurations allowing to control the cell length and aperture size. The cell design was optimized with heat and flow simulations for thermal characteristics, vacuum compatibility and generation medium properties. Finally, the cell system was experimentally validated by conducting high-order harmonic generation measurements using the 100 kHz high average power HR-1 laser system at the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI ALPS) facility. Such a robust, versatile and stackable gas cell arrangement can easily be adapted to different experimental geometries in both table-top laboratory systems and user-oriented facilities, such as ELI ALPS.

00:03 New laser breakthrough to help understanding of gravitational waves

Gravitational wave scientists from The University of Western Australia have led the development of a new laser mode sensor with unprecedented precision that will be used to probe the interiors of neutron stars and test fundamental limits of general relativity.

30.05.2022
05:53 Laser Generation of Near-GeV Low Emittance Positron Beams. (arXiv:2205.13850v1 [physics.acc-ph])

We report on the first spatial and spectral characterisation of near-GeV positron beams generated in a fully laser-driven configuration. The energy-resolved geometric emittance, source size and spectrum were simultaneously measured for electrons and positrons generated from a laser-wakefield accelerated electron beam impacting on a thin high-Z converter. More than $10^5$ positrons were observed within 5\% of 600 MeV, with a source size smaller than 100 $\mu$m and sub-micron geometric emittance, in agreement with numerical modelling. We conclude that the positron emittance was dominated by the transverse size of the primary electron beam at the converter. Minimising the drift distance between the electron source and the converter would allow for the generation of GeV-scale positron beams with micron-scale source size and normalised emittance of a few microns, using a 150 TW laser system. It is proposed that beams with these characteristics are suited for experimental studies of positron

28.05.2022
00:43 Robotic Laser Guides Dog Owners to Poop That Needs to be Picked Up (Video)

Keeping a dog at home is a very nice thing, providing their owners with lots of joy. But

27.05.2022
06:43 Enhanced collisionless laser absorption in strongly magnetized plasmas. (arXiv:2205.13478v1 [physics.plasm-ph])

Strongly magnetizing a plasma adds a range of waves that do not exist in unmagnetized plasmas and enlarges the laser-plasma interaction (LPI) landscape. In this paper, we use particle-in-cell (PIC) simulations to investigate strongly magnetized LPI in one dimension under conditions relevant for magneto-inertial fusion experiments, focusing on a regime where the electron-cyclotron frequency is greater than the plasma frequency and the magnetic field is at an oblique angle with respect to the wave vectors. We show that when the electron cyclotron frequency is about half the laser frequency, the laser light resonantly decays to magnetized plasma waves via primary and secondary instabilities with large growth rates. These distinct magnetic-field-controlled instabilities, which we collectively call two-magnon decays, are analogous to two-plasmon decays in unmagnetized plasmas. Since the oblique magnetic field introduces additional phase mixing mechanisms during wave-particle interactions,

06:43 Cost-Optimal System Performance Maps for Laser-Accelerated Sailcraft. (arXiv:2205.13138v1 [astro-ph.IM])

Breakthrough Starshot is an initiative to explore the Centauri system using laser-accelerated sailcraft. Earlier work produced a point design for a 0.2 c mission carrying 1 g of payload. The present work widens the design space to missions having 0.1 mg to 100 kt payload and 0.0001-0.99 c (6-60,000 au/yr) cruise velocity. Also, the beam director may now draw up to 5 GW of power directly from the grid to augment the power drawn from its energy storage system. Augmenting stored energy with grid power shrinks beam director capital cost by 1-5 orders of magnitude. The wider design space encompasses new possibilities: A 0.1 mg microbiome accelerated to 0.01 c in only 2 min by a beam director that expends \$6k worth of energy. A 10 kg Solar system cubesat accelerated to 0.001 c (60 au/yr) by a \$600M beam director that expends \$60M worth of energy per mission. A progression from cost-optimized point designs to whole performance maps has been made possible by replacing numerical trajectory 26.05.2022 09:32 On-demand multimode optical storage in a laser-written on-chip waveguide. (arXiv:2205.12762v1 [physics.optics]) Quantum memory is a fundamental building block for large-scale quantum networks. On-demand optical storage with a large bandwidth, a high multimode capacity and an integrated structure simultaneously is crucial for practical application. However, this has not been demonstrated yet. Here, we fabricate an on-chip waveguide in a$\mathrm {^{151}Eu^{3+}:Y_2SiO_5}$crystal with insertion losses of 0.2 dB, and propose a novel pumping scheme to enable spin-wave atomic frequency comb (AFC) storage with a bandwidth of 11 MHz inside the waveguide. Based on this, we demonstrate the storage of 200 temporal modes using the AFC scheme and conditional on-demand storage of 100 temporal modes using the spin-wave AFC scheme. The interference visibility between the readout light field and the reference light field is$99.0\% \pm 0.6\%$and$97\% \pm 3\%$for AFC and spin-wave AFC storage, respectively, indicating the coherent nature of this low-loss, multimode and integrated storage device. 09:32 Unveiling the relative timing jitter in counter propagating all normal dispersion (CANDi) dual-comb fiber laser. (arXiv:2205.12516v1 [physics.optics]) Counter-propagating all-normal dispersion (CANDi) fiber laser is an emerging high-energy single-cavity dual-comb laser source. Its relative timing jitter (RTJ), a critical parameter for dual-comb timing precision and spectral resolution, has not been comprehensively investigated. In this paper, we enhance the state-of-the-art CANDi fiber laser pulse energy from 1 nJ to 8 nJ. We then introduce a novel reference-free RTJ characterization technique that provides shot-to-shot measurement capability at femtosecond precision for the first time. The measurement noise floor reaches 1.6x10-7 fs2/Hz, and the corresponding integrated measurement precision is only 1.8 fs (1 kHz, 20 MHz). With this new characterization tool, we are able to study the physical origin of CANDi laser's RTJ in detail. We first verify that the cavity length fluctuation does not contribute to the RTJ. Then we measure the integrated RTJ to be 39 fs (1 kHz, 20 MHz) and identify the pump relative intensity noise (RIN) to be 25.05.2022 23:10 Archaeologists reveal pre-Hispanic cities in Bolivia with laser technology Several hundred settlements from the time between 500 and 1400 AD lie in the Bolivian Llanos de Mojos savannah and have fascinated archaeologists for years. Researchers have now visualized the dimensions of the largest known settlement of the so-called Casarabe culture. Mapping with the laser technology LIDAR indicates that it is an early urbanism with a low population density -- the only known case so far from the Amazon lowlands. The results shed new light on how globally widespread and diverse early urban life was and how earlier societies lived in the Amazon. 17:22 Fabrication of Microfluidic Chips Using Laser Click Deposition Sens. Diagn.DOI: 10.1039/D2SD00060A, Paper Open Access This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.Mengqi Lv, Xinyu He, Kai Zhou, Ben Niu, Wei Wei, Haoran Li, Shasha Liu, Hua Su, Wei WangHere we proposed a programmable and low-cost laser click deposition (LCD) method to form complicated CuO patterns as master templates for fabricating microfluidic chips. It was based on the heat-induced...The content of this RSS Feed (c) The Royal Society of Chemistry 05:06 Laser control strategies in full dimensional funneling dynamics: The case of pyrazine. (arXiv:2205.12163v1 [physics.chem-ph]) Motivated by the major role funneling dynamics plays in light-harvesting processes, we built some laser control strategies inspired from basic mechanisms such as interference and kicks, and apply them to the case of pyrazine. We are studying the internal conversion between the two excited states, the highest and directly reachable from the initial ground state being considered as a donor, and the lowest as an acceptor. The ultimate control objective is the maximum population deposit in the otherwise dark acceptor, from a two-step process: radiative excitation of the donor, followed by a conical-intersection-mediated funneling towards the acceptor. The overall idea is to first obtain the control field parameters (individual pulses leading frequency and intensity, duration and inter-pulse time delay) for tractable reduced dimensional models basically describing the conical intersection branching space. Once these parameters are optimized, they are fixed and used in full dimensional 05:06 Injection induced by coaxial laser interference in laser wakefield accelerators. (arXiv:2205.12083v1 [physics.plasm-ph]) A new injection scheme using the interference of two coaxial laser pulses is proposed for generating high quality beams in laser wakefield accelerators. In this scheme, a relatively loosely focused laser pulse drives the plasma wakefield, and a tightly focused laser pulse with similar intensity triggers interference ring pattern which creates onion-like multi sheaths in the plasma wakefield. Due to the wavefront curvature change after the focal position of the tightly focused laser, the innermost sheath of the wakefield expands, which slows down the effective phase velocity of the wakefield and triggers injection of plasma electrons. Particle-in-cell simulations show that high quality electron beams with low energy spread (a few per mill), high charge (hundred picocoulomb) and small emittance (sub millimeter milliradian) at the same time can be generated using moderate laser parameters for properly chosen phase differences between the two lasers. 04:25 Novel ultrasound-assisted laser technique removes arterial plaque safely and efficiently Atherosclerosis, a buildup of plaque, can lead to heart disease, artery disease, and chronic kidney disease and is traditionally treated by inserting and inflating a balloon to expand the artery. 24.05.2022 23:13 Emulating impossible 'unipolar' laser pulses paves the way for processing quantum information A laser pulse that sidesteps the inherent symmetry of light waves could manipulate quantum information, potentially bringing us closer to room temperature quantum computing. 13:43 Emulating impossible ‘unipolar’ laser pulses paves the way for processing quantum information A laser pulse that sidesteps the inherent symmetry of light waves could manipulate quantum information, potentially bringing us 08:02 Laser-actuated hermetic seals for integrated atomic devices. (arXiv:2205.10440v1 [physics.atom-ph]) Atomic devices such as atomic clocks and optically-pumped magnetometers rely on the interrogation of atoms contained in a cell whose inner content has to meet high standards of purity and accuracy. Glass-blowing techniques and craftsmanship have evolved over many decades to achieve such standards in macroscopic vapor cells. With the emergence of chip-scale atomic devices, the need for miniaturization and mass fabrication has led to the adoption of microfabrication techniques to make millimeter-scale vapor cells. However, many shortcomings remain and no process has been able to match the quality and versatility of glass-blown cells. Here, we introduce a novel approach to structure, fill and seal microfabricated vapor cells inspired from the century-old approach of glass-blowing. In particular we demonstrate opening and closing single-use zero-leak microfabricated valves, actuated exclusively by laser, and operating in the same way as the "make-seals" and "break-seals" found in the 23.05.2022 20:42 Emulating impossible 'unipolar' laser pulses paves the way for processing quantum information A laser pulse that sidesteps the inherent symmetry of light waves could manipulate quantum information, potentially bringing us closer to room temperature quantum computing. 10:43 Characteristics of ion beams by laser acceleration in the Coulomb explosion regime. (arXiv:2205.10140v1 [physics.plasm-ph]) In the Coulomb explosion acceleration regime, an ion bunch with a narrow energy range exhibits a thin shell shape with a certain diameter. The ion cloud has a layered structure of these ion bunches with different energies. The divergences of the ion bunch in the laser inclination direction and perpendicular to it are different in an oblique incidence laser. This indicates that the smaller the spot diameter of the laser pulse, the larger the divergence of the ion beam. In addition, theoretical formulas for the radius of the generated ion beam and the energy spectrum are derived, and they are shown to be in good agreement with the simulation results. 21.05.2022 09:23 Mixing laser- and x-ray-beams Unlike fictional laser swords, real laser beams do not interact with each other when they cross - unless the beams meet within a suitable material allowing for nonlinear light-matter interaction. In such a case, wave mixing can give rise to beams with changed colors and directions. 20.05.2022 22:50 Mixing laser- and x-ray-beams Unlike fictional laser swords, real laser beams do not interact with each other when they cross -- unless the beams meet within a suitable material allowing for nonlinear light-matter interaction. In such a case, wave mixing can give rise to beams with changed colors and directions. 21:03 Mixing laser beams and X-ray beams Unlike fictional laser swords, real laser beams do not interact with each other when they cross—unless the beams meet within a suitable material allowing for nonlinear light-matter interaction. In such a case, wave mixing can give rise to beams with changed colors and directions. 04:13 High-quality femtosecond laser surface micro/nano-structuring assisted by a thin frost layer. (arXiv:2205.09650v1 [physics.optics]) Femtosecond laser ablation has been demonstrated to be a versatile tool to produce micro/nanoscale features with high precision and accuracy. However, the use of high laser fluence to increase the ablation efficiency usually results in unwanted effects, such as redeposition of debris, formation of recast layer and heat-affected zone in or around the ablation craters. Here we circumvent this limitation by exploiting a thin frost layer with a thickness of tens of microns, which can be directly formed by the condensation of water vapor from the air onto the exposed surface whose temperature is below the freezing point. When femtosecond laser beam is focused onto the target surface covered with a thin frost layer, only the local frost layer around the laser-irradiated spot melts into water, helping to boost ablation efficiency, suppress the recast layer and reduce the heat-affect zone, while the remaining frost layer can prevent ablation debris from adhering to the target surface. By this 04:13 Parallel bandit architecture based on laser chaos for reinforcement learning. (arXiv:2205.09543v1 [cs.ET]) Accelerating artificial intelligence by photonics is an active field of study aiming to exploit the unique properties of photons. Reinforcement learning is an important branch of machine learning, and photonic decision-making principles have been demonstrated with respect to the multi-armed bandit problems. However, reinforcement learning could involve a massive number of states, unlike previously demonstrated bandit problems where the number of states is only one. Q-learning is a well-known approach in reinforcement learning that can deal with many states. The architecture of Q-learning, however, does not fit well photonic implementations due to its separation of update rule and the action selection. In this study, we organize a new architecture for multi-state reinforcement learning as a parallel array of bandit problems in order to benefit from photonic decision-makers, which we call parallel bandit architecture for reinforcement learning or PBRL in short. Taking a cart-pole 04:13 Parallel bandit architecture based on laser chaos for reinforcement learning. (arXiv:2205.09543v1 [cs.ET]) Accelerating artificial intelligence by photonics is an active field of study aiming to exploit the unique properties of photons. Reinforcement learning is an important branch of machine learning, and photonic decision-making principles have been demonstrated with respect to the multi-armed bandit problems. However, reinforcement learning could involve a massive number of states, unlike previously demonstrated bandit problems where the number of states is only one. Q-learning is a well-known approach in reinforcement learning that can deal with many states. The architecture of Q-learning, however, does not fit well photonic implementations due to its separation of update rule and the action selection. In this study, we organize a new architecture for multi-state reinforcement learning as a parallel array of bandit problems in order to benefit from photonic decision-makers, which we call parallel bandit architecture for reinforcement learning or PBRL in short. Taking a cart-pole 19.05.2022 17:01 Russia's laser weapon claim derided as propaganda Moscow says it has destroyed a drone with a laser, but Kyiv says it can't mask battlefield failure. 16:42 Laser annealing transmon qubits for high-performance superconducting quantum processors Quantum physicists aim to scale the number of qubits during quantum computing, while maintaining high-fidelity quantum gates; this is a challenging task due to the precise frequency requirements that accompany the process. Superconducting quantum processors with more than 50 qubits are currently actively available and these fixed frequency transmons are attractive due to their long coherence and noise immunity. A transmon is a type of a superconducting charge qubit designed to have reduced sensitivity to charge noise. In a new report now published in Science Advances, Eric J. Zhang and a team of scientists at IBM Quantum, IBM T.J. Watson Research Centre, New York, U.S., used laser annealing to selectively tune transmon qubits into the desired frequency patterns. The research team achieved a tuning precision of 18.5 MHz, without any measurable impact on quantum coherence, and envision facilitating selective annealing in this way to play a central role in fixed-frequency architectures. 06:52 Single-electron Nano-chip Free-electron Laser. (arXiv:2205.08741v1 [physics.optics]) A conventional free-electron laser is useful but large, driven by a beam with many relativistic electrons. Although, recently, keV electron beams have been used to excite broadband radiation from material chips, there remains a quest for a chip-size free-electron laser capable of emitting coherent radiation. Unfortunately, those keV emitters from electron microscopes or dielectric laser accelerator usually deliver a small current with discrete moving electrons separated by a distance of a few or tens of microns. To envisage a chip-size free-electron laser as a powerful research tool, we study in this paper achievable laser radiation from a single electron and an array of single electrons atop a nano-grating dielectric waveguide. In our study, thanks to the strong coupling between the electron and the guided wave in a structure with distributed feedback, a single 50-keV electron generates 1.5-um laser-like radiation at the Bragg resonance of a 31-um long silicon grating with a 400-nm 18.05.2022 18:12 Laser weapons used in Ukraine operation – Moscow The Russian military is using powerful lasers capable of destroying enemy drones on the Ukraine battlefield, Vice PM Borisov claimed Read Full Article at RT.com 09:25 Carrier-envelope phase controlled dynamics of relativistic electron beams in a laser-wakefield accelerator. (arXiv:2205.08374v1 [physics.plasm-ph]) In laser-wakefield acceleration, an ultra-intense laser pulse is focused into an underdense plasma in order to accelerate electrons to relativistic velocities. In most cases, the pulses consist of multiple optical cycles and the interaction is well described in the framework of the ponderomotive force where only the envelope of the laser has to be considered. But when using single-cycle pulses, the ponderomotive approximation breaks down, and the actual waveform of the laser has to be taken into account. In this paper, we use near-single cycle laser pulses to drive a laser-wakefield accelerator. We observe variations of the electron beam pointing on the order of 10 mrad in the polarisation direction, as well as 30% variations of the beam charge, locked to the value of the controlled laser carrier-envelope phase, in both nitrogen and helium plasma. Those findings are explained through particle-in-cell simulations indicating that low-emittance, ultra-short electron bunches are 17.05.2022 12:24 Temperatures colder than space achieved here on Earth using superconducting X-ray laser Using a superconducting X-ray laser, researchers at SLAC achieved a temperature 4 degrees Fahrenheit above absolute zero. 05:12 The clamped intensity of femtosecond laser pulses varying with gas pressure in the presence of external focusing. (arXiv:2205.06990v1 [physics.plasm-ph]) We perform a theoretical investigation of the clamped laser intensity inside the filament plasma as a function of gas pressure with external focusing. Unlike the clamped intensity under the selffocusing condition, which is independent on the gas pressure, the clamped intensity with external focusing decreases with the gas pressure. Our findings can explain the changes of the signals of femtosecond-laser-induced 391-nm forward emission and fluorescence with the nitrogen gas pressure. 16.05.2022 07:43 Prototype Development and Validation of a Beam-Divergence Control System for Free-Space Laser Communications. (arXiv:2205.06776v1 [eess.SY]) Being able to dynamically control the transmitted-beam divergence can bring important advantages in free-space optical communications. Specifically, this technique can help to optimize the overall communications performance when the optimum laser-beam divergence is not fixed or known. This is the case in most realistic space laser communication systems, since the optimum beam divergence depends on multiple factors that can vary with time, such as the link distance, or cannot be accurately known, such as the actual pointing accuracy. A dynamic beam-divergence control allows to optimize the link performance for every platform, scenario, and condition. NICT is currently working towards the development of a series of versatile lasercom terminals that can fit a variety of conditions, for which the adaptive element of the transmitted beam divergence is a key element. This manuscript presents a prototype of a beam-divergence control system designed and developed by NICT and Tamron to evaluate 07:43 Prototype Development and Validation of a Beam-Divergence Control System for Free-Space Laser Communications. (arXiv:2205.06776v1 [eess.SY]) Being able to dynamically control the transmitted-beam divergence can bring important advantages in free-space optical communications. Specifically, this technique can help to optimize the overall communications performance when the optimum laser-beam divergence is not fixed or known. This is the case in most realistic space laser communication systems, since the optimum beam divergence depends on multiple factors that can vary with time, such as the link distance, or cannot be accurately known, such as the actual pointing accuracy. A dynamic beam-divergence control allows to optimize the link performance for every platform, scenario, and condition. NICT is currently working towards the development of a series of versatile lasercom terminals that can fit a variety of conditions, for which the adaptive element of the transmitted beam divergence is a key element. This manuscript presents a prototype of a beam-divergence control system designed and developed by NICT and Tamron to evaluate 13.05.2022 08:43 LUXE: A new experiment to study non-perturbative QED in electron-LASER and photon-LASER collisions. (arXiv:2205.06096v1 [hep-ex]) The LUXE experiment (LASER Und XFEL Experiment) is a new experiment in planning at DESY Hamburg using the electron beam of the European XFEL. LUXE is intended to study collisions between a high-intensity optical laser and 16.5 GeV electrons from the XFEL electron beam, as well as collisions between the optical LASER and high-energy secondary photons. The physics objective of LUXE are processes of Quantum Electrodynamics (QED) at the strong-field frontier, where the electromagnetic field of the laser is above the Schwinger limit. In this regime, QED is non-perturbative. This manifests itself in the creation of physical electron-positron pairs from the QED vacuum, similar to Hawking radiation from black holes. LUXE intends to measure the positron production rate in an unprecedented LASER intensity regime. An overview of the LUXE experimental setup and its challenges will be given, followed by a discussion of the expected physics reach in the context of testing QED in the non-perturbative 08:43 Plasma shutter for improved heavy ion acceleration by ultra-intense laser pulses. (arXiv:2205.06088v1 [physics.plasm-ph]) In this work, we investigate the application of the plasma shutter for heavy ion acceleration driven by a high intensity laser pulse. We use particle-in-cell (PIC) and hydrodynamic simulations. The laser pulse, transmitted through the shutter, gains a steep-rising front and its peak intensity is locally increased at the cost of losing part of its energy. These effects have a direct influence on subsequent ion acceleration from the ultrathin target behind the shutter. In our 3D simulations of silicon nitride plasma shutter and a silver target, the maximal energy of high-$ Z $ions increases significantly when the shutter is included. Moreover, application of the plasma shutter results in focusing of ions towards the laser axis in the plane perpendicular to the laser polarization. The generated high energy ion beam has significantly lower divergence compared to the broad ion cloud, generated without the shutter. The effects of prepulses are also investigated assuming a double plasma 08:43 Nonadiabatic ab initio molecular dynamics including spin-orbit coupling and laser fields. (arXiv:2205.06051v1 [physics.chem-ph]) Nonadiabatic ab initio molecular dynamics (MD) including spin-orbit coupling (SOC) and laser fields is investigated as a general tool for studies of excited-state processes. Up to now, SOCs are not included in standard ab initio MD packages. Therefore, transitions to triplet states cannot be treated in a straightforward way. Nevertheless, triplet states play an important role in a large variety of systems and can now be treated within the given framework. The laser interaction is treated on a non-perturbative level that allows nonlinear effects like strong Stark shifts to be considered. As MD allows for the handling of many atoms, the interplay between triplet and singlet states of large molecular systems will be accessible. In order to test the method, IBr is taken as a model system, where SOC plays a crucial role for the shape of the potential curves and thus the dynamics. Moreover, the influence of the nonresonant dynamic Stark effect is considered. The latter is capable of 08:43 Controlling chaotic itinerancy in laser dynamics for reinforcement learning. (arXiv:2205.05987v1 [physics.optics]) Photonic artificial intelligence has attracted considerable interest in accelerating machine learning; however, the unique optical properties have not been fully utilized for achieving higher-order functionalities. Chaotic itinerancy, with its spontaneous transient dynamics among multiple quasi-attractors, can be employed to realize brain-like functionalities. In this paper, we propose a method for controlling the chaotic itinerancy in a multi-mode semiconductor laser to solve a machine learning task, known as the multi-armed bandit problem, which is fundamental to reinforcement learning. The proposed method utilizes ultrafast chaotic itinerant motion in mode competition dynamics controlled via optical injection. We found that the exploration mechanism is completely different from a conventional searching algorithm and is highly scalable, outperforming the conventional approaches for large-scale bandit problems. This study paves the way to utilize chaotic itinerancy for effectively 08:43 Controlling chaotic itinerancy in laser dynamics for reinforcement learning. (arXiv:2205.05987v1 [physics.optics]) Photonic artificial intelligence has attracted considerable interest in accelerating machine learning; however, the unique optical properties have not been fully utilized for achieving higher-order functionalities. Chaotic itinerancy, with its spontaneous transient dynamics among multiple quasi-attractors, can be employed to realize brain-like functionalities. In this paper, we propose a method for controlling the chaotic itinerancy in a multi-mode semiconductor laser to solve a machine learning task, known as the multi-armed bandit problem, which is fundamental to reinforcement learning. The proposed method utilizes ultrafast chaotic itinerant motion in mode competition dynamics controlled via optical injection. We found that the exploration mechanism is completely different from a conventional searching algorithm and is highly scalable, outperforming the conventional approaches for large-scale bandit problems. This study paves the way to utilize chaotic itinerancy for effectively 12.05.2022 20:33 Laser bursts drive fastest-ever logic gates A long-standing quest for science and technology has been to develop electronics and information processing that operate near 17:03 SLAC’s superconducting X-ray laser reaches operating temperature colder than outer space The X-ray facility, LCLS-II, will soon sharpen our view of how nature works on ultrasmall, ultrafast scales, impacting 04:32 Damage threshold evaluation of thin metallic films exposed to femtosecond laser pulses: the role of material thickness. (arXiv:2205.05342v1 [cond-mat.mtrl-sci]) The employment of femtosecond pulsed lasers has received significant attention due to its capability to facilitate fabrication of precise patterns at the micro- and nano- lengths scales. A key issue for efficient material processing is the accurate determination of the damage threshold that is associated with the laser peak fluence at which minimal damage occurs on the surface of the irradiated solid. Despite a wealth of previous reports that focused on the evaluation of the laser conditions that lead to the onset of damage, the investigation of both the optical and thermal response of thin films of sizes comparable to the optical penetration depth is still an unexplored area. In this report, a detailed theoretical analysis of the impact of various parameters such as the photon energies and material thickness on the damage threshold for various metals (Au, Ag, Cu, Al, Ni, Ti, Cr, Stainless Steel) is investigated. A multiscale physical model is used that correlates the energy 04:32 On-demand Plasmon Nanoparticle-Embedded Laser-Induced Periodic Surface Structures (LIPSSs) on Silicon for Optical Nanosensing. (arXiv:2205.05294v1 [physics.optics]) Ultrashort laser pulses allows to deliver electromagnetic energy to matter causing its localized heating that can be used for both material removal via ablation/evaporation and drive interface chemical reactions. Here, we showed that both mentioned processes can be simultaneously combined within straightforward laser nanotexturing of Si wafer in functionalizing solution to produce a practically relevant metal-semiconductor surface nano-morphology. Such unique hybrid morphology represent deep-subwavelength Si LIPSSs with a extremely short period down to 70 nm with their high-aspect-ratio nanotrenches loaded with controllable amount of plasmonic nanoparticles formed$via\$ laser-induced decomposition of the precursor noble-metal salts. Moreover, heat localization driving reduction process was utilized to produce surface morphology locally decorated with dissimilar plasmon-active nanoparticles. Light-absorbing deep-subwavelength Si LIPSSs loaded with controllable amount of noble-metal

04:32 A red fluorescent protein laser based on microbubble cavity with high stability and ultra-low threshold. (arXiv:2205.05220v1 [physics.optics])

Biological lasers show considerable potential in the biomedical field. Fluorescent protein (FP) is a type of biomaterial with good luminescence efficiency that can be used as the luminescent gain medium in biological lasers. Red FPs (RFPs) show higher cell/tissue permeability, lower cell phototoxicity, and relatively less background fluorescence than FPs based on other colors. RFPs can be used in vivo for deep tissue imaging. mCherry is the most extensively used high-quality RFP because of its short maturation time and stable luminescence properties. In this study, we employ mCherry FPs with a whispering gallery mode microbubble cavity to fabricate a protein laser. The laser resonator achieves a maximum quality factor (Q factor) of 10^8, which is the highest Q factor among the currently available FP lasers. Moreover, this laser exhibits the lowest threshold of 169 fJ, which can effectively ensure that the pump light does not damage the luminescent material. The prepared laser shows

11.05.2022
20:40 Laser bursts drive extremely fast logic gates

By clarifying the role of 'real' and 'virtual' charge carriers in laser-induced currents, researchers have taken a decisive step toward creating ultrafast computers.

19:33 Laser bursts drive fastest-ever logic gates

A long-standing quest for science and technology has been to develop electronics and information processing that operate near the fastest timescales allowed by the laws of nature.

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