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15.11.2018
17:50 Phys.orgTerahertz laser pulses amplify optical phonons in solids

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg/Germany presents evidence of the amplification of optical phonons in a solid by intense terahertz laser pulses. These light bursts excite atomic vibrations to very large amplitudes, where their response to the driving electric field becomes nonlinear and conventional description fails to predict their behavior.

05:10 Arxiv.org PhysicsLaser-induced acoustic desorption of thermally stable and unstable biomolecules. (arXiv:1811.05925v1 [physics.chem-ph])

We evaluated the effect of the laser-induced acoustic desorption (LIAD) process on thermally stable and unstable biomolecules. We found that the thermally labile glycine molecule fragmented following desorption via LIAD, due to the production of hot molecules from the LIAD process. We furthermore observed a rise in translational temperature with increasing desorption laser intensity, while the forward velocity was invariant with respect to the desorption laser intensity for both glycine and adenine molecules. The forward kinetic energy was in the range of the surface stress energy, which supports the previously proposed stress-induced desorption model for the laser-induced acoustic desorption process.

05:10 Arxiv.org PhysicsA novel approach to electron data background treatment in an online wide-angle spectrometer for laser-accelerated ion and electron bunches. (arXiv:1811.05842v1 [physics.plasm-ph])

Laser-based ion acceleration is driven by electrical fields emerging when target electrons absorb laser energy and consecutively leave the target material. A direct correlation between these electrons and the accelerated ions is thus to be expected and predicted by theoretical models. We report on a modified wide-angle spectrometer allowing the simultaneous characterization of angularly resolved energy distributions of both ions and electrons. Equipped with online pixel detectors, the RadEye1 detectors, the investigation of this correlation gets attainable on a single shot basis. In addition to first insights, we present a novel approach for reliably extracting the primary electron energy distribution from the interfering secondary radiation background. This proves vitally important for quantitative extraction of average electron energies (temperatures) and emitted total charge.

05:10 Arxiv.org PhysicsAb initio study of parity and time-reversal violation in laser-coolable triatomic molecules. (arXiv:1811.05749v1 [physics.chem-ph])

Electronic structure enhancement factors of simultaneous parity and time-reversal violation ($\mathcal{P,T}$-violation) caused by an electric dipole moment of the electron (eEDM) and scalar-pseudoscalar nucleon-electron current (SPNEC) interactions are reported for various metal mono-hydroxides, several of which are considered laser--coolable and promising candidates for an eEDM measurement. Electronic structure enhancements are calculated \textit{ab initio} within zeroth order regular approximation (ZORA) for CaOH, SrOH, BaOH, RaOH and YbOH. Scaling behavior with respect to nuclear charge numbers and the ratio of enhancement factors for both discussed sources of $\mathcal{P,T}$-violation are analyzed, which are crucial to obtain stringent bounds on parameters for new physics from experiments.

14.11.2018
07:56 Arxiv.org PhysicsHigh-harmonics of harmonics of a fiber laser: a milliwatt XUV ultrashort source. (arXiv:1811.05178v1 [physics.optics])

Recent progresses in femtosecond ytterbium-doped fiber laser technology areopening new perspectives in strong field physics and attosecond science. Highorder harmonic generation from these systems is particularly interesting because it provides high flux beams of ultrashort extreme ultraviolet radiation. A lot of efforts have been devoted to optimize the macroscopic generation parameters. Here we investigate the possibility of enhancing the single-atom response by producing high-harmonics from the second, third and fourth harmonics of a turnkey Yb-fiber laser at 1030 nm. We show that the harmonic efficiency is optimal when the process is driven by the third harmonic, producing 4.4 1014 photon/s at 18 eV, which corresponds to 1.3 mW average power.

13.11.2018
10:35 Arxiv.org PhysicsStatistical outliers in random laser emission. (arXiv:1811.04789v1 [physics.optics])

We provide theoretical and experimental evidence of statistical outliers in random laser emission that are not accounted for by the, now established, power-law tailed (L\'evy) distribution. Such outliers manifest themselves as single, large isolated spikes over an otherwise smooth background. A statistical test convincingly shows that their probability is larger than the one extrapolated from lower-intensity events. To compare with experimental data, we introduced the anomaly parameter that allows for an identification of such rare events from experimental spectral measurements and that agrees as well with the simulations of our Monte Carlo model. A possible interpretation in terms of Black Swans or Dragon Kings, large events having a different generation mechanism from their peers, is discussed.

10:35 Arxiv.org PhysicsDevelopment of an adjustable Kirkpatrick-Baez microscope for laser driven x-ray sources at CLPU. (arXiv:1811.04762v1 [physics.ins-det])

A promising prototype of a highly adjustable Kirkpatrick-Baez (KB) microscope has been designed, built and tested in a number of laser driven x-ray experiments using the high power (200TW) VEGA-2 laser system of the Spanish Centre for Pulsed Lasers (CLPU). The presented KB version consists of two, perpendicularly mounted, 500{\mu}m thick Silicon wafers, coated with a few tens of nm layer of Platinum unlike the conventional, coated, millimetre thick glass substrates, affording more bending flexibility and large adjustment range. According to simulations, and based on total external reflection, this KB offers a broad-band multi-keV reflection spectra, allowing more spectral tunablity than conventional Bragg crystals. In addition to be vacuum compatible, the prototype is characterised by a relatively small size (21cm x 31cm x 27cm) and permits remote control and modification of both the radius

10:35 Arxiv.org PhysicsRegular pulse generation from a microcavity laser operated at threshold. (arXiv:1811.04571v1 [physics.optics])

The generation of optical pulses at ultra low bias level, thus low energy cost, is explored in a commercial microcavity semiconductor laser in view of testing the principle of energy efficient information encoding in potential integrated schemes. Sequences of regular, highly nonlinear pulses with acceptable amplitude stability are obtained from a commercial device as potential sources of bits where the information is added by post-treatment (pulse removal). A discussion on the energy expenditure per bit is offered, together with the optimal frequency for pulse generation, which is found to lie slightly below the above-threshold value declared by the manufacturer.

10:35 Arxiv.org PhysicsAn all-fiber laser oscillating directly at single TE01 mode through ring-core fibers. (arXiv:1811.04269v1 [physics.optics])

Cylindrical vector beams (CVBs) have a wide range of applications owing to their particular polarization characteristics and optical field distributions. For the first time, an azimuthally polarized fiber laser without any polarization controller is proposed and demonstrated experimentally. The scheme is based on a self-designed ring-core fiber and transverse mode filter (TMF). The ring-core fiber can break the degeneracy of LP11 modes and make the TE01 mode propagate stably in the fiber laser. The TMF, which made from the ring-core fiber by depositing a layer of Aluminum on the cladding surface, can effectively suppress the modes other than TE01 mode. The fiber laser can stably operate at TE01 mode with a narrow 30dB linewidth of 0.18nm, which indicates the laser is polarization-maintained. This study opens a new avenue toward the true application of CVBs fiber lasers.

12.11.2018
21:13 Telegraph.co.ukChina shows off stealth fighter as it unveils new laser weapon that can shoot down missiles and spy planes

06:21 Arxiv.org PhysicsFormation of RbCs dimers using an elliptically polarized laser pulse. (arXiv:1811.03998v1 [physics.atom-ph])

We consider the formation of RbCs by an elliptically polarized laser pulse. By varying the ellipticity of the laser for sufficiently large laser intensity, we see that the formation probability presents a strong dependence, especially around ellipticity 1/ $\sqrt$ 2. We show that the analysis can be reduced to the investigation of the long-range interaction between the two atoms. The formation is mainly due to a small momentum shifts induced by the laser pulse. We analyze these results using the Silberstein's expressions of the polarizabilities, and show that the ellipticity of the field acts as a control knob for the formation probability, allowing significant variations of the dimer formation probability at a fixed laser intensity, especially in the region around an ellipticity of 1/ $\sqrt$ 2.

06:21 Arxiv.org PhysicsProbing fully non-perturbative QED with electron-laser collisions. (arXiv:1811.03990v1 [physics.plasm-ph])

In the present work, a scheme is proposed that can be used to probe the fully non-perturbative regime of quantum electrodynamics. The scheme considers the collision of a 100 GeV-class electron beam with a counterpropagating ultraintense electromagnetic pulse. To reduce the radiative losses by the electrons, it is unavoidable to use a pulse with ultrashort duration. Therefore, in two-dimensional particle-in-cell simulations, it is shown how one can convert a next-generation optical laser to an ultraintense ($I\approx 2.9\times 10^{24}$ Wcm$^{-2}$) attosecond (duration $\approx$ 150 as) pulse. It is shown that the contribution of high-order radiative corrections can be differentiated from the background in the particle spectra generated in the interaction.

06:21 Arxiv.org PhysicsTheoretical investigation of the HgF radical towards laser cooling and eEDM measurement. (arXiv:1811.03908v1 [physics.atom-ph])

In order to realize more sensitive eEDM measurement, it would be worthwhile to find some new laser-cooled molecules with larger internal effective electric field (E$_{eff}$), higher electric polarizability and longer lifetime of the eEDM measurement state. Here we explore the merits of mercuric monofluoride ($^{202}Hg^{19}F$, X$^ 2 {\Sigma}_{1/2}$) for its potential of laser cooling and eEDM measurement. We theoretically investigated the electronic, rovibrational and hyperfine structures and verified the highly diagonal Franck-Condon factors (FCFs) of the main transitions by the Rydberg-Klein-Rees inversion (RKR) method and the Morse approximation. Hyperfine manifolds of the X$^ 2 {\Sigma}_{1/2} (\nu=0$) rotational states were examined with the effective Hamiltonian approach and a feasible sideband modulation scheme was proposed. In order to enhance optical cycling, the microwave remixing

06:21 Arxiv.org PhysicsCompact single-pass laser frequency conversion to 852.3 nm and 780.2 nm based on PPMgO:LN bulk crystals and single-frequency diode-laser-seeded fiber amplifiers. (arXiv:1811.03799v1 [physics.atom-ph])

We report the device to produce single-frequency continuously-tunable 852.3 nm laser by single-pass sum-frequency generation (SFG) of two single-frequency diode-laser-seeded fiber amplifiers at 1560.5 nm and 1878.0 nm in a periodically-poled magnesium-oxide-doped lithium niobate (PPMgO:LN) bulk crystal. 276 mW of 852.3 nm laser is realized, the continuously-tunable range is more than 10 GHz. Also we are able to generate single-frequency continuously-tunable 780.2 nm laser by single-pass second-harmonic generation (SHG) with PPMgO:LN bulk crystals. Employing this laser system we could conveniently perform laser cooling and trapping as well as manipulating both cesium and rubidium atoms simultaneously, it has a great application in biatomic interferometer and cold CsRb dimer experiments.

09.11.2018
17:40 Phys.orgLaser system prevents contamination on aircraft surfaces

Scientists have developed a laser material processing method to produce textured surfaces that repel dirt and water. This technology will primarily be used in the aerospace industry.

07:40 Arxiv.org PhysicsLow-dispersion low-loss dielectric gratings for efficient ultrafast laser pulse compression at high average powers. (arXiv:1811.03091v1 [physics.ins-det])

We have developed low-dispersion (1480 l/mm), resonance-free, diffraction gratings made of dielectric materials resistant to femtosecond laser damage $(SiO_{2}/HfO_{2})$. A 14 cm diameter sample was fabricated resulting in a mean diffraction efficiency of 99.1% at {\lambda} = 810 nm with 0.4% uniformity using equipment which can fabricate gratings up to 1m diagonal. The implementation of these gratings in the compression of 30 fs pulses in an out-of-plane geometry can result in compressor efficiencies of ~95%. The measured laser absorption is 500x lower than current ultrafast petawatt-class compressor gratings which will enable a substantial increase in average power handling capabilities of these laser systems.

08.11.2018
23:59 ExtremeTech.comStudy Suggests Attracting Alien Astronomers with Giant Laser

A study from MIT’s Department of Aeronautics and Astronautics suggests Earth could make itself more visible to invite alien contact.
The post Study Suggests Attracting Alien Astronomers with Giant Laser appeared first on ExtremeTech.

11:56 Technology.orgWe Could Build a Powerful Laser and Contact Civilizations Within 20,000 Light-Years. But Should We?

A powerful laser is just the thing to announce our presence as a technological species in this arm

10:16 Arxiv.org PhysicsParametric study of cycle modulation in laser driven ion beams and acceleration field retrieval at femtosecond time scale. (arXiv:1811.03049v1 [physics.plasm-ph])

High frequency modulations appearing in the kinetic energy distribution of laser accelerated ions are proposed for retrieving the acceleration field dynamics at femtosecond time scale. Such an approach becomes possible if the laser-cycling field modulates the particle density in the ion spectra and produces quasi time stamps for analysis. We investigate target and laser parameters determining this effect and discuss the dependencies of the observed modulation. Our findings refine a basic mechanism, the Target Normal Sheath Acceleration, where an intense and ultrafast laser pulse produces a very strong electrical field at a plasma-vacuum interface. The field decays rapidly due to energy dissipation and forms a characteristic spectrum of fast ions streaming away from the interface. We show that the derived decay function of the field is in accordance with model predictions of the accelerating

10:16 Arxiv.org PhysicsMagnetic-enhanced modulation transfer spectroscopy and laser locking for 87Rb repump transition. (arXiv:1811.02852v1 [physics.atom-ph])

Locking of a laser frequency to an atomic or molecular resonance line is a key technique in applications of laser spectroscopy and atomic metrology. Modulation transfer spectroscopy (MTS) provides an accurate and stable laser locking method which has been widely used. Normally, the frequency of the MTS signal would drift due to Zeeman shift of the atomic levels and rigorous shielding of stray magnetic field around the vapor cell is required for the accuracy and stability of laser locking. Here on the contrary, by applying a transverse bias magnetic field, we report for the first time observation of a magnetic-enhanced MTS signal on the transition of 87Rb D2-line Fg=1 to Fe=0 (close to the repump transition of Fg=1 to Fe=2), with signal to noise ratio larger than 100:1. The error signal is immune to the external magnetic fluctuation. Compared to the ordinary MTS scheme, it provides a robust

07.11.2018
15:06 Technology.orgLaser technique may open door to more efficient clean fuels

Research by the University of Liverpool could help scientists unlock the full potential of new clean energy technologies.

06:07 Gizmag Could we – and should we – build a laser lighthouse to make first contact with aliens?

Whether there's life beyond Earth is one of the most profound questions we can ask, and finding out is a cornerstone of many a space mission. But if there is anybody out there, they might also be wondering the same thing, so maybe making ourselves easier to find could be an important part of our first contact strategy. A new MIT study outlines a way to use existing or near-future tech to build a kind of laser lighthouse to signal to our cosmic neighbors.
.. Continue Reading Could we – and should we – build a laser lighthouse to make first contact with aliens? Category: Space Tags: Exoplanet Extraterrestrial Laser MIT SETI Telescope

05:56 Arxiv.org PhysicsCoherent perfect absorber and laser for nonlinear waves in optical waveguide arrays. (arXiv:1811.02247v1 [physics.optics])

A localized non-Hermitian potential can operate as a coherent perfect absorber or as a laser for nonlinear waves. The effect is illustrated for an array of optical waveguides, with the central waveguide being either active or absorbing. The arrays situated to the left and to the right from the center can have different characteristics. The result is generalized to setups with the central waveguide carrying additional nonlinear dissipation or gain and to the two-dimensional arrays with embedded one-dimensional absorbing or lasing sub-arrays.

05:56 Arxiv.org PhysicsTheory of x-ray scattering from laser-driven electronic systems. (arXiv:1811.02246v1 [physics.optics])

We describe, within the framework of quantum electrodynamics, an interaction between a non-resonant hard x-ray pulse and an electronic system in the presence of a temporally periodic laser field driving electron dynamics in this system. We apply Floquet theory to describe the laser-driven electronic system, and then obtain the scattering probability of an arbitrary nonresonant x-ray pulse from such a system employing the density-matrix formalism. We show that the scattering probability can be connected to the time-dependent electron density of the driven electronic system only under certain conditions, in particular, if the bandwidth of the probe x-ray pulse is sufficiently narrow to spectroscopically resolve transitions to different final states. A special focus is laid on application of the theory to laser-driven crystals in a strongly nonperturbative regime. We show how the

06.11.2018
08:49 Arxiv.org PhysicsA micro channel-cut crystal X-ray monochromator for a self-seeded hard X-ray free-electron laser. (arXiv:1811.01860v1 [physics.ins-det])

A channel-cut Si(111) crystal with a channel width of 90 $\mu$m was developed for achieving reflection self-seeding in hard X-ray free-electron lasers (XFELs). With the crystal, a monochromatic seed pulse is produced from a broadband XFEL pulse generated in the first-half undulators with an optical delay of 119 fs at 10 keV. The small optical delay allows a temporal overlap between the seed optical pulse and the electron bunch by using a small magnetic chicane for the electron beam at the middle of the undulator section. A peak reflectivity reached 67%, which is a reasonable value as compared with the theoretical one of 81%. By using this monochromator, a monochromatic seed pulse without broadband background in spectrum was obtained at SACLA with a conversion efficiency from a broadband XFEL pulse of $\sim 2 \times 10^{-2}$, which is $\sim 10$ times higher than that of transmission

08:49 Arxiv.org PhysicsSingle-shot temporal profile measurement of a soft X-ray laser pulse. (arXiv:1811.01858v1 [physics.ins-det])

We report an original method allowing to recover the temporal profile of any kind of soft X-ray laser pulse in single-shot operation. We irradiated a soft X-ray multilayer mirror with an intense infrared femtosecond laser pulse in a traveling wave geometry and took advantage of the sudden reflectivity drop of the mirror to reconstruct the temporal profile of the soft X-ray pulse. We inferred a pulse shape with a duration of a few ps in good agreement with numerical calculations and experimental work.

08:49 Arxiv.org PhysicsCompact highly efficient 2.1-W continuous-wave mid-IR Fe:ZnSe coherent source pumped by Er:ZBLAN fiber laser. (arXiv:1811.01682v1 [physics.optics])

We report the compact and robust coherent source operating in mid-IR based on Fe:ZnSe chalcogenide gain medium optically pumped by Er:ZBLAN fiber laser. The output power of 2.1 W with 59% slope efficiency with respect to absorbed pump power at liquid nitrogen cooling is achieved. We show that strong re-absorption at high pump power and iron ion doping concentrations leads to the continuous tuning of central wavelength from 4012 to 4198 nm. Robustness of high power Er:ZBLAN fiber laser combined with prominent spectroscopic properties of Fe:ZnSe media pave the way for the development of reliable tunable CW mid-IR sources for scientific and industrial purposes.

08:49 Arxiv.org PhysicsParticle Velocity Distributions in Developing Magnetized Collisionless Shocks in Laser-Produced Plasmas. (arXiv:1811.01528v1 [physics.plasm-ph])

We present the first laboratory observations of time-resolved electron and ion velocity distributions in forming, magnetized collisionless shocks. Thomson scattering of a probe laser beam was used to observe the interaction of a laser-driven, supersonic piston plasma expanding through a magnetized ambient plasma. From the Thomson-scattered spectra we measure time-resolved profiles of electron density, temperature, and ion flow speed, as well as spatially-resolved magnetic fields from proton radiography. We observe direct evidence of the sweeping up and acceleration of ambient ions, magnetic field compression, and the subsequent deformation of the piston ion flow, key steps in shock formation. Even before the shock has fully formed, we observe strong density compressions and electron heating associated with the pile up of piston ions. The results demonstrate that laboratory experiments can

08:49 Arxiv.org PhysicsSupervised learning of an opto-magnetic neural network with ultrashort laser pulses. (arXiv:1811.01375v1 [cs.ET])

The explosive growth of data and its related energy consumption is pushing the need to develop novel, brain-inspired and energy-efficient schemes and materials for data processing and storage. Here, we demonstrate experimentally that Co/Pt films can be used as artificial synapses by manipulating their magnetization state using circularly-polarized ultrashort optical pulses at room temperature. We also show an efficient implementation of supervised perceptron learning on an opto-magnetic neural network, built from such magnetic synapses. Importantly, we demonstrate that the optimization of synaptic weights can be achieved using a global feedback mechanism, such that the learning does not rely on external storage or additional optimization schemes. These results suggest there is high potential for realizing artificial neural networks using optically-controlled magnetization in technologically

08:49 Arxiv.org PhysicsControlling the size distribution of nanoparticles through the use of physical boundaries during laser ablation in liquids. (arXiv:1811.01365v1 [physics.plasm-ph])

A simple, yet effective method of controlling the size and size distributions of nanoparticles produced as a result of laser ablation of target material is presented. The method employs the presence of physical boundaries on either sides of the ablation site. In order to demonstrate the potential of the method, experiments have been conducted with copper and titanium as the target materials that are placed in two different liquid media (water and isopropyl alcohol). The ablation of the target material immersed in the liquid medium has been carried out using an Nd:YAG laser. Significant differences in the size and size distributions are observed in the cases of nanoparticles produced with and without confining boundaries. It is seen that for any given liquid medium and the target material, the mean size of the nanoparticles obtained with the boundary-fitted target surface is consistently

08:49 Arxiv.org PhysicsPerturbative approach to the self-focusing of intense X-ray laser beam propagating in thermal quantum plasma. (arXiv:1811.01358v1 [physics.plasm-ph])

In this theoretical study, the problem of self-focusing of an X-ray intense laser beam in the thermal quantum plasma is studied. Using a relativistic fluid model and taking into account the hydrodynamic pressure of degenerate electrons in the zero temperature limit, the nonlinear momentum equation of electrons is solved by means of a perturbative method and the nonlinear current density of the relativistic degenerate electrons is obtained. Saving only the third-order nonlinearity of the laser beam amplitude, a nonlinear equation describing the interaction of laser beam with the quantum plasma is derived. It is shown that considering the nonlinearity of system through solving nonlinear equation of degenerate electron leads to the originally different wave equation in comparison with outcomes of the approach in which the permittivity of longitudinal waves of quantum plasma is problematically

08:49 Arxiv.org PhysicsInteraction of relativistically intense laser pulses with long-scale near critical plasmas for optimization of laser based sources of MeV elec-trons and gamma-rays. (arXiv:1811.01278v1 [physics.plasm-ph])

Experiments were performed to study electron acceleration by intense sub-picosecond laser pulses propagating in sub-mm long plasmas of near critical electron density (NCD). Low density foam layers of 300-500 um thickness were used as targets. The NCD-plasma was produced by a mechanism of a super-sonic ionization when a well-defined separate ns-pulse was sent onto the foam-target forerunning the relativistic main pulse. The effect of the relativistic laser pulse channeling and creation of quasi-static azimuthal magnetic and radial electric fields that keeps electrons in the channel ensured effective coupling of the laser energy into energetic electrons. Application of sub-mm thick low density foam layers provided substantial increase of the electron acceleration path in a NCD-plasma compared to the case of freely expanding plasmas created in the interaction of the ns-laser pulse with solid

08:49 Arxiv.org PhysicsDispersion of the laser pulse through propagation in underdense plasmas. (arXiv:1811.01164v1 [physics.plasm-ph])

The propagation of the laser pulses in the underdense plasma is a very crucial aspect of laser-plasma interaction process. In this work, we explored the two regimes of laser propagation in plasma, one with $a_0 < 1$ and other with $a_0 \gtrsim 10$. For $a_0<1$ case, we used a cold relativistic fluid model, wherein apart from immobile ions no further approximations are made. The effect of the laser pulse amplitude, pulse duration, and plasma density is studied using the fluid model and compared with the expected scaling laws and also with the PIC simulations. The agreement between the fluid model and the PIC simulations are found to be excellent. Furthermore, for $a_0 \gtrsim 10$ case, we used the PIC simulations alone. The delicate interplay between the conversion from the electromagnetic field energy to the longitudinal electrostatic fields results in the dispersion and so the

08:49 Arxiv.org PhysicsMid IR hollow core fiber gas laser emitting at 4.6 um. (arXiv:1811.01140v1 [physics.optics])

Emission at 4.6 um was observed from an N2O filled hollow core fiber laser. 8-ns pump pulses at 1.517 um excited a vibrational overtone resulting in lasing on an R and P branch fundamental transition from the upper pump state. At optimum gas pressure of 80 Torr a photon conversion efficiency of 9% and a slope efficiency of 3% was observed from a mirrorless laser. The laser threshold occurred at an absorbed pump energy of 150 nJ in a 45-cm long fiber with 85 {\mu}m core diameter. The observed dependence of the laser output on gas pressure is shown to be a result of line broadening and relaxation rates.

08:49 Arxiv.org PhysicsOptimization of femtosecond laser processing in liquids. (arXiv:1811.01046v1 [physics.app-ph])

In this paper we analyze femtosecond laser processing of metals in liquids searching for optimal conditions for predictable ablation. Incident laser pulses are stretched or compressed, self-focused and scattered on bubbles and on surface waves in the liquid environment. Influence of these effects on the laser intensity distribution on the target surface is discussed and optimal processing parameters are suggested.

08:49 Arxiv.org CSSupervised learning of an opto-magnetic neural network with ultrashort laser pulses. (arXiv:1811.01375v1 [cs.ET])

The explosive growth of data and its related energy consumption is pushing the need to develop novel, brain-inspired and energy-efficient schemes and materials for data processing and storage. Here, we demonstrate experimentally that Co/Pt films can be used as artificial synapses by manipulating their magnetization state using circularly-polarized ultrashort optical pulses at room temperature. We also show an efficient implementation of supervised perceptron learning on an opto-magnetic neural network, built from such magnetic synapses. Importantly, we demonstrate that the optimization of synaptic weights can be achieved using a global feedback mechanism, such that the learning does not rely on external storage or additional optimization schemes. These results suggest there is high potential for realizing artificial neural networks using optically-controlled magnetization in technologically

03:00 ScienceDaily.comLaser architecture can create complex structures to probe, control matter

A new laser architecture called the universal light modulator is an intriguing new tool to probe and control matter.

05.11.2018
22:32 ScienceDaily.comLaser tech could be fashioned into Earth's 'porch light' to attract alien astronomers

If extraterrestrial intelligence exists somewhere in our galaxy, a new study proposes that laser technology on Earth could, in principle, be fashioned into something of a planetary porch light -- a beacon strong enough to attract attention from as far as 20,000 light years away.

20:23 Phys.orgLaser architecture can create complex structures to probe, control matter

Lasers have a unique ability to precisely drive, manipulate, control, and probe matter utilizing an incredible variety of methods. While they often operate behind the scenes, lasers are the backbone of revolutionary science and technology—including research advances that were the basis for the 2018 Nobel Prize in Physics.

19:56 ScienceDaily.comLaser blasting antimatter into existence

Antimatter is an exotic material that vaporizes when it contacts regular matter. If you hit an antimatter baseball with a bat made of regular matter, it would explode in a burst of light. It is rare to find antimatter on Earth, but it is believed to exist in the furthest reaches of the universe. Amazingly, antimatter can be created out of thin air...

18:41 Phys.orgLaser blasting antimatter into existence

Antimatter is an exotic material that vaporizes when it contacts regular matter. If you hit an antimatter baseball with a bat made of regular matter, it would explode in a burst of light. It is rare to find antimatter on Earth, but it is believed to exist in the furthest reaches of the universe. Amazingly, antimatter can be created out of thin air—scientists can create blasts of matter and antimatter simultaneously using light that is extremely energetic.

16:39 Phys.orgExisting laser technology could be fashioned into Earth's 'porch light' to attract alien astronomers

If extraterrestrial intelligence exists somewhere in our galaxy, a new MIT study proposes that laser technology on Earth could, in principle, be fashioned into something of a planetary porch light—a beacon strong enough to attract attention from as far as 20,000 light years away.

11:26 Arxiv.org PhysicsConfiguration of vortex-antivortex lattices at output mirror of wide-area microchip laser. (arXiv:1811.01008v1 [nlin.PS])

Square vortex lattices predicted theoretically and experimentally observed in diode-pumped solid state microchip lasers are shown to have a remarkable symmetry. These lattices are formed by counter-rotating vortices. The interaction of vortices with nonlinear gain medium leads to precession of vortices and collective excitations with dynamics identical to acoustical and optical vibrations of atomic lattices.

11:26 Arxiv.org PhysicsRelative Intensity Noise in a Multi-Stokes Brillouin Laser. (arXiv:1811.00861v1 [physics.ins-det])

We investigate the Relative Intensity Noise (RIN) properties of a multi-Stokes Brillouin fiber ring laser. We experimentally analyse intensity noise of each Stokes waves and study the noise dynamics of the cascaded Brillouin scattering process. We observe up to 20 dB/Hz intensity noise reduction compared to that of the RIN input pump laser. We examine the impact of the fiber ring quality factor on the laser RIN features such as amplitude reduction and relaxation frequency. A numerical model based on a set of coupled-mode equations replicate the experimental observations; confirming the class B like behavior of a multi-Stokes Brillouin laser. Our study enables to determine the optimal parameter values to operate the multi-Stokes laser in the low noise regime.

08:19 News-Medical.NetRussian physicists develop method for narrowing emission spectrum of diode laser

Russian physicists have developed a method for drastically narrowing the emission spectrum of an ordinary diode laser, like that in a laser pointer. This makes their device a useful replacement for the more complex and expensive single-frequency lasers, enabling the creation of compact chemical analyzers that can fit into a smartphone, cheap lidars for self-driving cars, as well as security and structural health monitoring systems on bridges, gas pipelines, and elsewhere.

03.11.2018
14:34 Technology.orgNASA Team Investigates Ultrafast Laser Machining for Multiple Spaceflight Applications

An ultrafast laser that fires pulses of light just 100 millionths of a nanosecond in duration could potentially

02.11.2018
14:39 Phys.orgPhysicists upgrade cheap diode laser for use in precise measurements

Russian physicists have developed a method for drastically narrowing the emission spectrum of an ordinary diode laser, like that in a laser pointer. This makes their device a useful replacement for the more complex and expensive single-frequency lasers, enabling the creation of compact chemical analyzers that can fit into smartphones, cheap lidars for self-driving cars, as well as security and structural health monitoring systems on bridges, gas pipelines and elsewhere. The study was published Oct. 26 in Nature Photonicsand was co-authored by researchers from the Russian Quantum Center (RQC), the Moscow Institute of Physics and Technology (MIPT), Lomonosov Moscow State University (MSU), and Samsung R&D Institute Russia.

05:43 Arxiv.org PhysicsLaser Calibration System in JUNO. (arXiv:1811.00354v1 [physics.ins-det])

A UV laser calibration system is developed for the Jiangmen Underground Neutrino Observatory (JUNO), a 20-kton liquid scintillator-based, long baseline reactor anti-neutrino experiment. This system is capable of delivering fast laser pulses (<1 ns) into the detector with a photon intensity ranging from hundreds of keV to a few TeV equivalent energy. An independent intensity monitoring system is developed for this laser, which has achieved a < 0.3% relative uncertainty. Such a system will be used to calibrate the response of JUNO photosensors and electronics in situ to a sub-percent precision.

05:43 Arxiv.org PhysicsApplication of laser biospeckle analysis for assessment of seed priming techniques. (arXiv:1811.00324v1 [physics.optics])

Seed priming is one of the well-established and low cost method to improve seed germination properties, productivity, and stress tolerance in different crops. It is a pre-germination treatment that partially hydrates the seed and allows controlled imbibition. This stimulates and induces initial germination process, but prevents radicle emergence. Consequently, treated seeds are fortified with enhanced germination characteristics, improved physiological parameters, uniformity in growth, and improved capability to cope up with different biotic and abiotic stresses. Existing techniques for evaluating the effectiveness of seed priming suffer from several drawbacks, including very high operating time, indirect and destructive analysis, bulky experimental arrangement, high cost, and require extensive analytical expertise. To circumvent these drawbacks, we propose a biospeckle based technique to

05:43 Arxiv.org PhysicsThe Mu-MASS (MuoniuM lAser SpectroScopy) experiment. (arXiv:1811.00310v1 [physics.atom-ph])

We present a new experiment, Mu-MASS, aiming for a 1000-fold improvement in the determination of the 1S-2S transition frequency of Muonium (M), the positive-muon/electron bound state. This substantial improvement beyond the current state-of-the-art relies on the novel cryogenic M converters and confinement techniques we developed, on the new excitation and detection schemes which we implemented for positronium spectroscopy and the tremendous advances in generation of UV radiation. This experiment is planned to be performed at the Paul Scherrer Institute (PSI). Interesting anomalies in the muon sector have accumulated: notably the famous anomalous muon magnetic moment (g-2) and the muonic hydrogen Lamb shift measurement which prompted the so-called proton charge radius puzzle. These tantalizing results triggered vibrant activity on both experimental and theoretical sides. Different

01.11.2018
19:15 Phys.orgNASA team investigates ultrafast laser machining for multiple spaceflight applications

An ultrafast laser that fires pulses of light just 100 millionths of a nanosecond in duration could potentially revolutionize the way that NASA technicians manufacture and ultimately assemble instrument components made of dissimilar materials.

18:07 Phys.orgLaser-activated silk sealants outperform sutures for tissue repair

NIBIB funded researchers have developed laser-activated nanomaterials that integrate with wounded tissues to form seals that are superior to sutures for containing body fluids and preventing bacterial infection.

08:36 Arxiv.org PhysicsNm-sized cryogenic hydrogen clusters for a laser-driven proton source. (arXiv:1810.13371v1 [physics.plasm-ph])

A continuous cryogenic hydrogen cluster-jet target has been developed for laser-plasma interaction studies, in particular as a source for the acceleration of protons. Major advantages of the cluster-jet target are the compatibility with pulsed high repetition lasers and the absence of debris. The cluster-jet target was characterized using the Mie-scattering technique allowing to determine the cluster size and to compare it with an empirical prediction. In addition, an estimation of the cluster beam density was performed. The system was implemented at the high power laser system ARCTURUS and first successful measurements show the acceleration of protons after irradiation by high intensity laser pulses with a repetition rate of five Hertz.

08:36 Arxiv.org PhysicsWavelength agile multi-photon microscopy with a fiber amplified diode laser. (arXiv:1810.13018v1 [physics.optics])

Multi-photon microscopy is a powerful tool in biomolecular research. Less complex and more cost effective excitation light sources will make this technique accessible to a broader community. Especially semiconductor diode seeded fiber lasers have proven to be robust, low cost and easy to use. However, their wavelength tuning range is often limited, so only a limited number of fluorophores can be accessed. Therefore, different approaches have been proposed to extend the spectral coverage of these lasers. Recently, we showed that four-wave mixing (FWM) assisted stimulated Raman scattering (SRS) can be harnessed to red-shift high power pulses from 1064 nm to a narrowband output at 1122 nm and 1186 nm and therefore extend the number of accessible fluorophores. In this contribution, we show the applicability of all three wavelengths for multi-photon microscopy and analyze the

03:22 NewScientist.ComA zap from a laser could make bigger quantum computers possible

A breakthrough in controlling entanglement with laser or microwave pulses could let us make more accurate quantum computers without having to cool them down

31.10.2018
18:37 RFI.frHow laser eye surgery was discovered - RFI's interview with 2018 Nobel laureate

French Nobel laureate for physics Gérard Mourou, one of the inventors of the laser technology with which eye-correction surgery is done, talks about the incredible accident that led to its discovery.

17:32 Nanowerk.comLaser-activated silk nanosealants outperform sutures for tissue repair

Researchers have developed laser-activated nanomaterials that integrate with wounded tissues to form seals that are superior to sutures for containing body fluids and preventing bacterial infection.

04:14 Arxiv.org PhysicsSub-cycle quantum electrodynamics in strongly laser-driven semiconductors. (arXiv:1810.12721v1 [physics.optics])

Electrodynamical processes induced in complex systems like semiconductors by strong electromagnetic fields, have traditionally/conventionally been described using semi-classical approaches. Although these approaches, allowed the investigation of ultrafast dynamics in solids culminating in multi-petahertz electronics, they do not provide any access in the quantum optical nature of the interaction as they treat the driving-field classically and unaffected by the interaction. Here, using a full quantum-optical approach, we demonstrate that the sub-cycle electronic response in a strongly driven semiconductor crystal is imprinted in the quantum-state of the driving-field resulting in non-classical light-states carrying the information of the interaction. This vital step towards strong-field ultrafast quantum electrodynamics unravels information inaccessible by conventional approaches and leads to

04:14 Arxiv.org PhysicsFirst demonstration of temperature control enabled high power mode-switchable fiber laser. (arXiv:1810.12485v1 [physics.optics])

A transverse mode-switching method was proposed and demonstrated in a high-power ytterbium-doped fiber oscillator. 17.8 W LP11 mode laser was obtained, and it could be switched to 16.5 W LP01 mode laser through temperature control.

30.10.2018
23:11 Phys.orgLaser technique may open door to more efficient clean fuels

Research by the University of Liverpool could help scientists unlock the full potential of new clean energy technologies.

23:07 ScienceDaily.comLaser technique may open door to more efficient clean fuels

Electrocatalysts have shown promise as a way to efficiently convert waste CO2 into clean fuels, but the mechanisms by which they operate are often unknown making it hard for researchers to design new ones in a rational manner. New research demonstrates a laser-based spectroscopy technique that can be used to study the electrochemical reduction of CO2 in-situ and provide much-needed insights into these complex chemical pathways.

20:28 WhatReallyHappened.comRUSSIA DEVELOPING 21ST CENTURY PULSE AND LASER WEAPONS TO DESTROY U.S SATELLITES

As we approach the third decade of the 21st century, the battle over space will feature prominently. We recall back in the 1980’s, the infamous war-hawk U.S president, Reagan, promised that the Americans would be able to produce a ‘Star Wars’ weapons system, and the program was based on the use of lasers.
But it’s Russia that has made leaps and bounds in the development of space weapons, and weapons that can reach space. The S-500 for example, can reach those objects in near earth orbit which we casually refer to as ‘space’.

07:02 Arxiv.org PhysicsVortex modes supported by spin-orbit coupling in a laser with saturable absorption. (arXiv:1810.12208v1 [nlin.PS])

We introduce a system of two component two-dimensional (2D) complex Ginzburg-Landau equations (CGLEs) with spin-orbit-coupling (SOC) describing a wide-aperture microcavity laser with saturable gain and absorption. We report families of two-component self-trapped dissipative laser solitons in this system. The SOC terms are represented by the second-order differential operators, which sets the difference, $|\Delta S|=2$, between the vorticities of the two components. We have found stable solitons of two types: vortex-antivortex (VAV) and semi-vortex (SV) bound states, featuring vorticities $\left( -1,+1\right)$ and $\left( 0,2\right)$, respectively. In previous works, 2D localized states of these types were found only in models including a trapping potential, while we are dealing with the self-trapping effect in the latteraly unconfined (free-space) model. The SV states are stable in a narrow

07:02 Arxiv.org PhysicsDirect observation of plasma waves and dynamics induced by laser-accelerated electron beams. (arXiv:1810.11813v1 [physics.acc-ph])

Plasma wakefield acceleration (PWFA) is a novel acceleration technique with promising prospects for both particle colliders and light sources. However, PWFA research has so far been limited to a few large-scale accelerator facilities world-wide. Here, we present first results on plasma wakefield generation using electron beams accelerated with a 100-TW-class Ti:Sa laser. Due to their ultrashort duration and high charge density, the laser-accelerated electron bunches are suitable to drive plasma waves at electron densities in the order of $10^{19}$ cm$^{-3}$. We capture the beam-induced plasma dynamics with femtosecond resolution using few-cycle optical probing and, in addition to the plasma wave itself, we observe a distinctive transverse ion motion in its trail. This previously unobserved phenomenon can be explained by the ponderomotive force of the plasma wave acting on the ions, resulting

07:02 Arxiv.org PhysicsStochastic electron heating in the laser and quasi-static electric and magnetic fields. (arXiv:1810.11574v1 [physics.plasm-ph])

The dynamics of ultrarelativistic electrons in the intense laser radiation and quasi-static electromagnetic fields both along and across to the laser propagating direction are studied in the 3/2 dimensional Hamiltonian framework. It is shown that the unperturbed oscillations of the ultrarelativistic electron in these electric fields could exhibit a long tail of harmonics which makes an onset of stochastic electron motion be a primary candidate for electron heating. The Poincar\'e mappings describing the electron motions in the laser and electric fields only are derived from which the criterions for instability are obtained. It follows that for both transverse and longitudinal electric fields, there exist upper limits of the stochastic electron energy depending on the laser intensity and electric field strength. Specifically, these maximum stochastic energies are enhanced by a strong laser

29.10.2018
09:35 Arxiv.org PhysicsAn extended-cavity diode laser at 497 nm for laser cooling and trapping of neutral strontium. (arXiv:1810.11434v1 [physics.atom-ph])

We present the first extended-cavity diode laser in Littrow configuration operating in the cyan wavelength range around 497 nm. The gallium-nitride based diode laser features a free-space output with up to 60 mW, operates in a single frequency mode, is tunable over a range of more than 8 nm and has a Lorentzian linewidth of less than 90 kHz. A detailed characterization of the tuning capabilities of the diode laser and its emission spectrum is provided. This compact, simple and low cost laser source replaces more complex systems based on frequency doubling and therefore simplifies the development of future compact and mobile optical clocks based on neutral strontium. Applications include efficient repumping of strontium atoms from the $5s5p$ $^3P_2$ state and the 9.8 MHz broad $5s5p$ $^3P_2 \rightarrow 5s5d$ $^3D_3$ transition might be of interest for sub-Doppler cooling.

09:35 Arxiv.org PhysicsMode-locked dysprosium fiber laser: picosecond pulse generation from 2.97 to 3.30 {\mu}m. (arXiv:1810.11114v1 [physics.optics])

Mode-locked fiber laser technology to date has been limited to sub-3 {\mu}m wavelengths, despite significant application-driven demand for compact picosecond and femtosecond pulse sources at longer wavelengths. Erbium- and holmium-doped fluoride fiber lasers incorporating a saturable absorber are emerging as promising pulse sources for 2.7--2.9 {\mu}m, yet it remains a major challenge to extend this coverage. Here, we propose a new approach using dysprosium-doped fiber with frequency shifted feedback (FSF). Using a simple linear cavity with an acousto-optic tunable filter, we generate 33 ps pulses with up to 2.7 nJ energy and 330 nm tunability from 2.97 to 3.30 {\mu}m (3000--3400 cm^-1)---the first mode-locked fiber laser to cover this spectral region and the most broadly tunable pulsed fiber laser to date. Numerical simulations show excellent agreement with experiments and also offer new

28.10.2018
13:59 Gizmag US Marines want non-lethal laser weapon that shouts at people a kilometer away

The US Marine Corps wants a new laser weapon system that is not only non-lethal, but can yell at people. In a recently closed call for applications, the Marines outlined the requirements for the new vehicle-mobile Scalable Compact Ultra-short Pulse Laser System (SCUPLS) that can disorient and cause pain without injury, yet can also send clear, audible warnings as far as 1,000 m (3,300 ft).
.. Continue Reading US Marines want non-lethal laser weapon that shouts at people a kilometer away Category: Military Tags: Laser weapon US Marines

26.10.2018
23:38 Gizmag Window-mounted laser device tells firefighters where to go

When firefighters arrive at a house fire, it's crucial that they know the location of people who may need their help the most. The LED- and laser-equipped Beam Ready BR-1000H is designed with that in mind, and it's just hit Kickstarter.
.. Continue Reading Window-mounted laser device tells firefighters where to go Category: Around The Home Tags: Emergencies Firefighting Home Kickstarter

15:57 Phys.orgA fine-tuned laser welds more effectively

Using laser technology Empa scientists optimized a technique to weld the electronics of implantable pacemakers and defibrillators into a titanium case. The medtech company Medtronic is now using the method worldwide to produce these devices.

11:22 Technology.orgNew laser breakthrough

In the last half-century, laser technology has grown into a multi-billion-dollar global industry and used in everything from

10:59 Technology.orgGas-detecting laser device gets an upgrade

University of Michigan researchers have refined a gas-sniffing device so that it can detect poisonous gases and explosives

03:39 Arxiv.org PhysicsRaman Spectroscopy of Diesel and Gasoline Engine-Out Soot Using Different Laser Power. (arXiv:1810.10701v1 [physics.app-ph])

We studied engine-out soot samples collected from a heavy-duty direct-injection diesel engine and a port-fuel injection gasoline spark-ignition engine. The two types of soot samples were characterized using Raman spectroscopy with different laser power. A Matlab program using least-square-method with trust-region-reflective algorithm was developed for curve fitting. We used a DOE (design of experiments) method to avoid local convergence. This method was used for two-band fitting and three-band fitting. The fitting results were used to determine the intensity ratio of D and G Raman bands. We find that high laser power may cause oxidation of soot samples, which gives higher D/G intensity ratio. Diesel soot has consistently higher amorphous/graphitic carbon ratio and thus higher oxidation reactivity, in comparison to gasoline soot, which is revealed by the higher D/G intensity ratio in Raman

03:39 Arxiv.org PhysicsElectron dynamics in laser and quasi-static transverse electric and longitudinal magnetic fields. (arXiv:1810.10670v1 [physics.plasm-ph])

By deriving the 3/2 dimensional Hamiltonian method for electrons in the intense laser radiation and quasi-static transverse electric and longitudinal magnetic fields, the electron heating mechanisms are examined both for low harmonic resonance of electron frequency in the static fields with the laser frequency and for high harmonic resonances where the overlap of broadened resonances causes the stochastic heating. In the former case, it shows that the efficient electron heating is only possible for the first harmonic resonance where the electron gyrofrequency in the strong longitudinal magnetic field is matching the laser frequency. In the latter case it demonstrates that the stochasticity is weakened due to the presence of weak magnetic field which will terminate the stochastic heating when exceeding a critical strength. The maximum electron energies in the measurement of ponderomotive

25.10.2018
06:21 Arxiv.org PhysicsCoexisting frequency combs spaced by an octave in a monolithic quantum cascade laser. (arXiv:1810.10203v1 [physics.optics])

Quantum cascade lasers are proving to be instrumental in the development of compact frequency comb sources at mid-infrared and terahertz frequencies. Here we demonstrate a heterogeneous terahertz quantum cascade laser with two active regions spaced exactly by one octave. Both active regions are based on a four-quantum well laser design and they emit a combined 3~mW peak power at 15~K in pulsed mode. The two central frequencies are 2.3~THz (bandwidth 300~GHz) and 4.6~THz (bandwidth 270~GHz). The structure is engineered in a way that allows simultaneous operation of the two active regions in the comb regime, serving as a double comb source as well as a test bench structure for all waveguide internal self-referencing techniques. Narrow RF beatnotes ($\sim$ 15~kHz) are recorded showing the simultaneous operation of the two combs, whose free-running coherence properties are investigated by means

06:21 Arxiv.org CSDeepLSR: Deep learning approach for laser speckle reduction. (arXiv:1810.10039v1 [cs.CV])

We present a deep learning approach for laser speckle reduction ('DeepLSR') on images illuminated with a multi-wavelength, red-green-blue laser. We acquired a set of images from a variety of objects illuminated with laser light, both with and without optical speckle reduction, and an incoherent light-emitting diode. An adversarial network was then trained for paired image-to-image translation to transform images from a source domain of coherent illumination to a target domain of incoherent illumination. When applied to a new image set of coherently-illuminated test objects, this network reconstructs incoherently-illuminated images with an average peak signal-to-noise ratio and structural similarity index of 36 dB and 0.91, respectively, compared to 30 dB and 0.88 using optical speckle reduction, and 30 dB and 0.88 using non-local means processing. We demonstrate proof-of-concept for

24.10.2018
21:52 ScienceDaily.comFirst demonstration of 'random, transistor' laser which can be manipulated at nanoscale

Lasers are poised to take another step forward. Researchers have been able to control the direction of a laser's output beam by applying external voltage.

09:05 Arxiv.org PhysicsFree space laser telecommunication through fog. (arXiv:1810.09800v1 [physics.optics])

Atmospheric clearness is a key issue for free space optical communications (FSO). We present the first active method to achieve FSO through clouds and fog, using ultrashort high intensity laser filaments. The laser filaments opto-mechanically expel the droplets out of the beam and create a cleared channel for transmitting high bit rate telecom data at 1.55 microns. The low energy required for the process allows considering applications to Earth-satellite FSO and secure ground based optical communication, with classical or quantum protocols.

23.10.2018
22:40 Phys.orgResearchers demonstrate 'random, transistor' laser that can be manipulated at nanoscale

In the last half-century, laser technology has grown into a multi-billion-dollar global industry and has been used in everything from optical-disk drives and barcode scanners to surgical and welding equipment.

15:51 Phys.orgGas-detecting laser device gets an upgrade

University of Michigan researchers have refined a gas-sniffing device so that it can detect poisonous gases and explosives in less than half a second.

04:37 Arxiv.org Quantitative BiologyModel of vibrones in quantum photosynthesis as an analog of model of laser. (arXiv:1810.09334v1 [physics.chem-ph])

Mechanism of vibronic amplification of transport of excitons was discussed in relation to quantum photosynthesis. Vibrones (some modes of vibrations of molecules) are observed experimentally in photosynthetic systems. In the present paper we discuss a model of vibronic amplification of quantum transfer where generation of vibrones as a coherent vibrational mode is described by an analog of semiclassical theory of laser. We consider two models --- a model of nonequilibrium three level system with vibronic mode, and some variant of a model of laser without inversion. We conjecture that dark states discussed in relation to quantum photosynthesis might be related to mechanism of vibronic "laser" without inversion which amplifies the transfer of excitons. We prove that in presence of vibronic mode transfer rate of excitons increases and compute dependence of the transfer rate on parameters of the

04:37 Arxiv.org PhysicsModel of vibrones in quantum photosynthesis as an analog of model of laser. (arXiv:1810.09334v1 [physics.chem-ph])

Mechanism of vibronic amplification of transport of excitons was discussed in relation to quantum photosynthesis. Vibrones (some modes of vibrations of molecules) are observed experimentally in photosynthetic systems. In the present paper we discuss a model of vibronic amplification of quantum transfer where generation of vibrones as a coherent vibrational mode is described by an analog of semiclassical theory of laser. We consider two models --- a model of nonequilibrium three level system with vibronic mode, and some variant of a model of laser without inversion. We conjecture that dark states discussed in relation to quantum photosynthesis might be related to mechanism of vibronic "laser" without inversion which amplifies the transfer of excitons. We prove that in presence of vibronic mode transfer rate of excitons increases and compute dependence of the transfer rate on parameters of the

04:37 Arxiv.org PhysicsRadiation friction force effects on electron dynamics in ultra-intensity laser pulse. (arXiv:1810.09254v1 [physics.plasm-ph])

The electron dynamics in the ultra-high intensity laser pulse with radiation friction force in theLandau-Lifshitz form are studied. It is demonstrated that widely used approximation, where onlythe term dominating the dissipation of electron kinetic energy is retained in the expression for theradiation friction, is incorrect for the case of diverging electron trajectories. As a matter of fact, forlarge friction force effects, all components of the radiation friction force in the Landau-Lifshitz formhave the same order in the equation of electron motion, being equally important for both electrontrajectory and thus energy gain in the case of diverging electron trajectories (e.g. determined bythe superposition of few electromagnetic waves).

04:37 Arxiv.org PhysicsBoosting terahertz-radiation power with two-color circularly polarized midinfrared laser pulses. (arXiv:1810.08834v1 [physics.atom-ph])

A way to considerably enhance terahertz radiation, emitted in the interaction of intense mid-infrared laser pulses with atomic gases, in both the total energy and the electric-field amplitude is suggested. The scheme is based on the application of a two-color field consisting of a strong circularly polarized mid-infrared pulse with wavelengths of $1.6\div 4\,\mu{\rm m}$ and its linearly or circularly polarized second harmonic of lower intensity. By combining the strong-field approximation for the ionization of a single atom with particle-in-cell simulations of the collective dynamics of the generated plasma it is shown that the application of such two-color circularly polarized laser pulses may lead to an order-of-magnitude increase in the energy emitted in the terahertz frequency domain as well as in a considerable enhancement in the maximal electric field of the terahertz pulse. Our results

22.10.2018
07:16 Arxiv.org PhysicsAngular Distributions of Thomson Scattering in Combined Laser and Magnetic fields. (arXiv:1810.08333v1 [physics.plasm-ph])

Angular distributions of Thomson scattering are researched in the combined fields with a circularly polarization of laser field and a strong uniform magnetic field. The trajectories of the electron and the dependence of it on the initial phase are also given. It is found that the angular distributions with respect to the azimuthal angle show twofold symmetry whatever the laser intensity, the order of harmonics, the resonance parameter, and the initial axial momentum are. On the other hand, the radiation with respect to the polar angle is mainly distributed in two regions which are roughly symmetric of the laser propagation. In addition, the larger the laser intensity, the resonance parameters, the initial axial momentum are, the closer radiation is to the laser propagation direction. Besides, a new possibility of X-ray production is indicated. That is to say, with appropriate choice of laser

07:16 Arxiv.org PhysicsVersatile laser-free trapped-ion entangling gates. (arXiv:1810.08300v1 [quant-ph])

We present a general theory for laser-free entangling gates with trapped-ion hyperfine qubits, using either static or oscillating magnetic-field gradients combined with a pair of uniform microwave fields symmetrically detuned about the qubit frequency. By transforming into a `bichromatic' interaction picture, we show that either ${\hat{\sigma}_{\phi}\otimes\hat{\sigma}_{\phi}}$ or ${\hat{\sigma}_{z}\otimes\hat{\sigma}_{z}}$ geometric phase gates can be performed. The gate basis is determined by selecting the microwave detuning. The driving parameters can be tuned to provide intrinsic dynamical decoupling from qubit frequency fluctuations. The ${\hat{\sigma}_{z}\otimes\hat{\sigma}_{z}}$ gates can be implemented in a novel manner which eases experimental constraints. We present numerical simulations of gate fidelities assuming realistic parameters.

07:16 Arxiv.org PhysicsInfrared laser magnetometry with a NV doped diamond intracavity etalon. (arXiv:1810.08253v1 [physics.optics])

We propose an hybrid laser system consisting of a semiconductor external cavity laser associated to an intra-cavity diamond etalon doped with nitrogen-vacancy color centers. We consider laser emission tuned to the infrared absorption line that is enhanced under the magnetic field dependent nitrogen-vacancy electron spin resonance and show that this architecture leads to a compact solid-state magnetometer that can be operated at room-temperature. The sensitivity to the magnetic field limited by the photon shot-noise of the output laser beam is estimated to be around $250~\mathrm{fT/\sqrt{Hz}}$. Unlike usual NV center infrared magnetometry, this method would not require an external frequency stabilized laser. Since the proposed system relies on the competition between the laser threshold and an intracavity absorption, such laser-based optical sensor could be easily adapted to a broad variety of

18.10.2018
03:58 Arxiv.org PhysicsAlpha decay in intense laser fields: Calculations using realistic nuclear potentials. (arXiv:1810.07331v1 [physics.atom-ph])

We calculate the effect of intense laser fields on nuclear alpha decay processes, using realistic and quantitative nuclear potentials. We show that alpha decay rates can indeed be modified by strong laser fields to some finite extent. We also predict that alpha decays with lower decay energies are relatively easier to be modified than those with higher decay energies, due to longer tunneling paths for the laser field to act on. Furthermore, we predict that modifications to angle-resolved penetrability are easier to achieve than modifications to angle-integrated penetrability.

03:58 Arxiv.org PhysicsMicrocontroller based scanning transfer cavity lock for long-term laser frequency stabilization. (arXiv:1810.07256v1 [physics.ins-det])

We present a compact all-digital implementation of a scanning transfer cavity lock (STCL) for long-term laser frequency stabilization. An interrupt-based, event-centric state machine is employed to realize the STCL, with the capability to correct for frequency drifts in the slave laser frequency due to measured changes in the lab environmental conditions to within 0.9 MHz for master laser and slave laser wavelengths of 556 nm and 798 nm, respectively. The slave laser is also demonstrated to dynamically scan over a wide frequency range, allowing us to interrogate atomic transitions.

17.10.2018
06:41 Arxiv.org PhysicsControlling the quantum number distribution and yield of Rydberg states via the duration of the laser pulse. (arXiv:1810.07164v1 [physics.atom-ph])

We show that the distribution of quantum numbers of Rydberg states does not only depend on the field strength and wavelength of the laser which the atom is exposed to, but that it also changes significantly with the duration of the laser pulse. We provide an intuitive explanation for the underlying mechanism and derive a scaling law for the position of the peak in the quantum number distribution on the pulse duration. The new analytic description for the electron's movement in the superposed laser and Coulomb field (applied in the study of quantum numbers) is then used to explain the decrease of the Rydberg yield with longer pulse durations. This description stands in contrast to the concepts that explained the decrease so far and also reveals that approximations which neglect Coulomb effects during propagation are not sufficient in cases such as this.

06:41 Arxiv.org PhysicsDynamics of Ultrafast Laser Ablation of Water. (arXiv:1810.06946v1 [physics.app-ph])

Ultrafast laser ablation is an extremely precise and clean method of removing material, applied in material processing as well as medical applications. And due to its violent nature, it tests our understanding of the interplay between optics, condensed matter physics and fluid dynamics. In this manuscript, we experimentally investigate the femtosecond laser induced explosive vaporization of water at a water/gas interface on the micron-scale through several time-scales. Using time-resolved microscopy in reflection mode, we observe the formation of a hot electron plasma, an explosively expanding water vapor and a shockwave propelled into the surrounding gas. We study this fs-laser induced water vapor expansion dynamics in the presence of different atmospheres, i.e. Helium, air and tetrafluoroethane. We use the Sedov-Taylor model to explain the expansion of the water vapor and estimate the

06:41 Arxiv.org PhysicsUltraintense femtosecond magnetic nanoprobes induced by azimuthally polarized laser beams. (arXiv:1810.06942v1 [physics.optics])

We report a novel scheme to generate laser-induced, ultrafast, intense (Tesla scale), spatially isolated, magnetic fields. Three-dimensional particle-in-cell simulations show that a femtosecond azimuthally-polarized infrared vector beam, aimed to a conducting circular aperture, produces an intense axially polarized tip-shaped femtosecond magnetic field, extending over micrometer distances and being isolated from the electric field. Our results are backed-up by an analytic model, demonstrating the underlying physics and guiding for optimal parameters. In particular, we find the conditions under which the magnetic nanoprobe is substantially enhanced, reaching 4 T when driven by a $10^{11}$ W/cm$^2$ laser field, which reflects a selective enhancement by a factor of $\sim$6. Our scheme offers a promising tool to control, probe and tailor magnetic nanodomains in femtosecond timescales through pure

06:41 Arxiv.org PhysicsRadiation emission in laser-wakefields driven by structured laser pulses with orbital angular momentum. (arXiv:1810.06929v1 [physics.plasm-ph])

High-intensity X-ray sources are invaluable tools, enabling experiments at the forefront of our understanding of materials science, chemistry, biology, and physics. Laser-plasma electron accelerators are sources of high-intensity X-rays, as electrons accelerated in wakefields emit short-wavelength radiation due to betatron oscillations. While applications such as phase-contrast imaging with these betatron sources have already been demonstrated, others would require higher photon number and would benefit from increased tunability. In this paper we demonstrate, through detailed 3D simulations, a novel configuration for a laser-wakefield betatron source that increases the energy of the X-ray emission and also provides increased flexibility in the tuning of the X-ray photon energy. This is made by combining two Laguerre-Gaussian pulses with non-zero net orbital angular momentum, leading to a

06:41 Arxiv.org PhysicsOptical rogue wave in random distributed feedback fiber laser. (arXiv:1810.06867v1 [physics.optics])

The famous demonstration of optical rogue wave (RW)-rarely and unexpectedly event with extremely high intensity-had opened a flourishing time for temporal statistic investigation as a powerful tool to reveal the fundamental physics in different laser scenarios. However, up to now, optical RW behavior with temporally localized structure has yet not been presented in random fiber laser (RFL) characterized with mirrorless open cavity, whose feedback arises from distinctive distributed multiple scattering. Here, thanks to the participation of sustained and crucial stimulated Brillouin scattering (SBS) process, experimental explorations of optical RW are done in the highly-skewed transient intensity of an incoherently-pumped standard-telecom-fiber-constructed RFL. Furthermore, threshold-like beating peak behavior can also been resolved in the radiofrequency spectroscopy. Bringing the concept of

06:41 Arxiv.org PhysicsLaser stimulated deexcitation of Rydberg antihydrogen atoms. (arXiv:1810.06736v1 [physics.atom-ph])

Antihydrogen atoms are routinely formed at CERN in a broad range of Rydberg states. Ground-state anti-atoms, those useful for precision measurements, are eventually produced through spontaneous decay. However given the long lifetime of Rydberg states the number of ground-state antihydrogen atoms eventually usable is small. Therefore, it is of high interest to efficiently stimulate the decay in order to retain a higher fraction of ground-state atoms for measurements. We propose a method that optimally mix the high angular momentum states with low ones enabling to stimulate, using a broadband frequency laser, the deexcitation toward low-lying states, which then spontaneously decay to ground-state. We evaluated the method in realistic antihydrogen experimental conditions. For instance, starting with an initial distribution of atoms within the $n=20-30$ manifolds, as formed through charge

16.10.2018
09:23 Arxiv.org PhysicsDirect measurement of electron numbers created at infrared laser-induced ionization of various gases. (arXiv:1810.06153v1 [physics.plasm-ph])

In this work we present temporally resolved measurements of electron numbers in infrared laser-induced plasmas. The experiments were conducted in O2, Xe, Ar, N2, Kr and CO at room temperature and atmospheric pressure by a 800 nm femtosecond laser pulse. Rayleigh Microwave Scattering (RMS) technique was used to directly measure the electron numbers using homodyne detection system. Plasma decay after the laser pulse was governed by two competing processes, creation of new electrons by ionization of the metastable atoms and loss of the electrons due to dissociative recombination.

09:23 Arxiv.org PhysicsUltrafast dynamic evolution of multilevel systems in medium-strength laser fields. (arXiv:1810.05860v1 [physics.atom-ph])

The ultrafast dynamic evolution of an atomic system under medium-strength laser fields is studied by performing transient absorption measurement. An analytical model developed from perturbation theory with a modified transition dipole moment is presented to explain the spectral features of the multilevel system. By fitting the measured absorption spectra to the model, the system's dynamic evolution is quantified by different amplitude and phase modulation factors in the pump--probe and probe--pump scenarios. This study provides a way to understand laser--matter interaction in the transition area between the strong-field and weak-field regimes.

15.10.2018
22:50 Gizmag Felik uses AI to take your pet laser-huntin'

It's no secret that cats and dogs can get bored when they're left home alone all day, which is why we've seen things such as pet-entertaining robots. Felik doesn't go quite that far, but instead uses artificial intelligence to let your critter "hunt" a moving laser beam.
.. Continue Reading Felik uses AI to take your pet laser-huntin' Category: Pets Tags: Cats Dogs Indiegogo Laser

18:04 Phys.orgStudy shows what happens when ultrafast laser pulses, not heat, cause a material to change phase

The way that ordinary materials undergo a phase change, such as melting or freezing, has been studied in great detail. Now, a team of researchers has observed that when they trigger a phase change by using intense pulses of laser light, instead of by changing the temperature, the process occurs very differently.

05:05 Arxiv.org MathSixth-order schemes for laser--matter interaction in Schr\"odinger equation. (arXiv:1810.05412v1 [math.NA])

Control of quantum systems via lasers has numerous applications that require fast and accurate numerical solution of the Schr\"odinger equation. In this paper we present three strategies for extending any sixth-order scheme for Schr\"odinger equation with time-independent potential to a sixth-order method for Schr\"odinger equation with laser potential. As demonstrated via numerical examples, these schemes prove effective in the atomic scaling as well as the semiclassical regime, and are a particularly appealing alternative to time-ordered exponential splittings when the laser potential is highly oscillatory or known only at specific points in time (on an equispaced grid, for instance).
These schemes are derived by exploiting the linear in space form of the time dependent potential under the dipole approximation (whereby commutators in the Magnus expansion reduce to a simpler form),

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