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# Laser

20.05.2019
17:21 Phys.orgScientists develop polariton nano-laser operating at room temperature

A room temperature polariton nano-laser has been demonstrated, along with several related research findings, regarding topics such as polariton physics at the nanoscale and also applications in quantum information systems. The research was published in the journal, Science Advances.

15:16 Technology.orgWhat Is A Laser Marking Machine and Its Use In The Automotive Industry

In the automotive industry, labeling and marking of products is an integral part of the manufacturing process. With

08:31 Arxiv.org PhysicsInvestigating the use of the hydrogen cyanide (HCN) as an absorption media for laser spectroscopy. (arXiv:1905.07272v1 [physics.optics])

The laser spectroscopy is a fundamental approach for the realisation of traceable optical frequency standards. In the $1.55\,\mu$m wavelength band, widely used in telecommunications, the acetylene is the typical and the most widespread absorption media. We present our investigation of using the hydrogen cyanide (HCN) as a cost-efficient and readily available alternative, that also provides a wider frequency span (from $1527\,$nm to $1563\,$nm). We have compared the practical aspects of using new absorption media in comparison to existing experience with the acetylene with an outlook to carry out an independent measurement of the entire spectra. The results should contribute to the future inclusion of the HCN spectroscopic data into the Mise en pratique, thus allowing for the use of HCN as a reference for the realisation of traceable laser standards.

08:31 Arxiv.org PhysicsRandomized Spectral Sampling for Efficient Simulation of Laser Propagation through Optical Turbulence. (arXiv:1905.07074v1 [physics.optics])

We present a new method for the generation of atmospheric turbulence phase screens based on the frequency shift property of the Fourier transform. This method produces low spatial frequency distortions without additional computation time penalties associated with methods using subharmonic subgrids. It is demonstrated that for simulations of atmospheric turbulence with finite outer scales, the performance of our method with respect to the statistical phase structure of the screen meets or exceeds other methods with respect to agreement with theory. We outline small-scale accuracy issues associated with modelling non-Kolmogorov spectral power laws using existing techniques, and propose a solution. For simulations of long-range propagation through atmospheric optical turbulence, our method provides various advantages over standard methods.

08:31 Arxiv.org PhysicsTunable X-ray source by Thomson scattering during laser-wakefield acceleration. (arXiv:1905.07029v1 [physics.acc-ph])

We report results on all-optical Thomson scattering intercepting the acceleration process in a laser wakefield accelerator. We show that the pulse collision position can be detected using transverse shadowgraphy which also facilitates alignment. As the electron beam energy is evolving inside the accelerator, the emitted spectrum changes with the scattering position. Such a configuration could be employed as accelerator diagnostic as well as reliable setup to generate x-rays with tunable energy.

01:32 Technology.orgNew laser microscope could be used to detect and treat diseases like skin cancer

Surgeries require cutting, right? Scalpels were invented for a reason. However, a new invention from The University of

18.05.2019
11:36 RT.comCheap 'shots' & attacks at light speed: Why laser weaponry is a trend for 21st century

Lasers are commonly seen as a 'weapon of the future' – and that future is already here as they are making it into the military. Laser systems have unique properties, opening new ways of waging warfare, RT's military analyst says. Read Full Article at RT.com

17.05.2019
15:59 Phys.orgLaser of sound promises to measure extremely tiny phenomena

Most people are familiar with optical lasers through their experience with laser pointers. But what about a laser made from sound waves?

15:08 RT.com‘Laser weapons’ to define Russia’s military potential in 21st century – Putin

Russian leader Vladimir Putin proposed to examine ‘the first practical results’ of using the Peresvet combat laser system by the army, saying that laser warfare technology will play a crucial role in the nation’s military might. Read Full Article at RT.com

10:00 Arxiv.org PhysicsTrapping laser excitation during collisions limits the lifetime of ultracold molecules. (arXiv:1905.06846v1 [physics.atom-ph])

The lifetime of nonreactive ultracold bialkali gases was thought to be limited by sticky collisions that amplify three-body loss. We show that the sticking times were previously overestimated and cannot explain the observed loss. Instead, we consider excitation of long-lived collision complexes by the trapping laser. We use a quasiclassical statistical model of the nuclear motion and ab initio potential energy and dipole moment surfaces for excited states of NaK+NaK complexes. We show typical excitation rates are two orders of magnitude faster than the dissociation rate. This leads to effective two-body loss, as observed in several experiments. Using longer wavelengths or lower laser intensities may somewhat increase the lifetime, whereas further improvement requires non-optical trapping or shielding from collisions.

10:00 Arxiv.org PhysicsLaser frequency upconversion in plasmas with finite ionization rates. (arXiv:1905.06399v1 [physics.plasm-ph])

Laser frequency can be upconverted in a plasma undergoing ionization. For finite ionization rates, the laser pulse energy is partitioned into a pair of counter-propagating waves and static transverse currents. The wave amplitudes are determined by the ionization rates and the input pulse duration. The strongest output waves can be obtained when the plasma is fully ionized in a time that is shorter than the pulse duration. The static transverse current can induce a static magnetic field with instant ionization, but it dissipates as heat if the ionization time is longer than a few laser periods. This picture comports with experimental data, providing a description of both laser frequency upconverters as well as other laser-plasma interaction with evolving plasma densities.

16.05.2019
13:43 Euronews.NetWatch: Eiffel Tower celebrates 130th anniversary with laser show

Rising 324 metres, the "Iron Lady" was designed by engineer Gustave Eiffel for the 1889 Universal Exhibition.

05:35 Arxiv.org PhysicsAn X-Ray Regenerative Amplifier Free-Electron Laser Using Diamond Pinhole MIrrors. (arXiv:1905.06279v1 [physics.acc-ph])

Free-electron lasers (FELs) have been built ranging in wavelength from long-wavelength oscillators using partial wave guiding through ultraviolet through hard x-ray FELs that are either seeded or start from noise (SASE). Operation in the x-ray spectrum has relied on single-pass SASE due either to the lack of seed lasers or difficulties in the design of x-ray mirrors. However, recent developments in the production of diamond crystal Bragg reflectors point the way to the design of regenerative amplifiers (RAFELs) which are, essentially, low-Q x-ray free-electron laser oscillators (XFELOs) that out-couple a large fraction of the optical power on each pass. A RAFEL using a six-mirror resonator providing out-coupling of 90% or more through a pinhole in the first downstream mirror is proposed and analyzed using the MINERVA simulation code for the undulator interaction and the Optics Propagation

05:35 Arxiv.org PhysicsA Laser-based Time Calibration System for the MEG II Timing Counter. (arXiv:1905.06270v1 [physics.ins-det])

We have developed a new laser-based time calibration system for the MEG II timing counter dedicated to timing measurement of positrons. The detector requires precise timing alignment between $\sim\,$500 scintillation counters. In this study, we present the calibration system which can directly measure the time offset of each counter relative to the laser-synchronized pulse. We thoroughly tested all the optical components and the uncertainty of this method is estimated to be 24 ps. In 2017, we installed the full system into the MEG II environment and performed a commissioning run. This method shows excellent stability and consistency with another method. The proposed system provides a precise timing alignment for SiPM-based timing detectors. It also has potential in areas such as TOF-PET.

05:35 Arxiv.org PhysicsExit momentum and instantaneous ionization rate of nonadiabatic tunneling ionization in elliptically polarized laser fields. (arXiv:1905.06162v1 [physics.atom-ph])

Based on the strong-field approximation, we obtain analytical expressions for the initial momentum at the tunnel exit and instantaneous ionization rate of tunneling ionization in elliptically polarized laser fields with arbitrary ellipticity. The tunneling electron reveals a nonzero offset of the initial momentum at the tunnel exit in the elliptically polarized laser field. We find that the transverse and longitudinal components of this momentum offset with respect to the instantaneous field direction are directly related to the time derivatives of the instantaneous laser electric field along the angular and radial directions, respectively. We further show that the nonzero initial momentum at the tunnel exit has a significant influence on the laser phase dependence of the instantaneous ionization rate in the nonadiabatic tunneling regime.

05:35 Arxiv.org PhysicsRMT: R-matrix with time-dependence. Solving the semi-relativistic, time-dependent Schrodinger equation for general, multi-electron atoms and molecules in intense, ultrashort, arbitrarily polarized laser pulses. (arXiv:1905.06156v1 [physics.comp-ph])

RMT is a program which solves the time-dependent Schrodinger equation for general, multielectron atoms, ions and molecules interacting with laser light. As such it can be used to model ionization (single-photon, multi-photon and strong-field), recollision (high-harmonic generation, strong-field rescattering), and more generally absorption or scattering processes with a full account of the multielectron correlation effects in a time-dependent manner. Calculations can be performed for targets interacting with ultrashort, intense laser pulses of long-wavelength and arbitrary polarization. Calculations for atoms can optionally include the Breit-Pauli correction terms for the description of relativistic (in particular, spin-orbit) effects.

05:35 Arxiv.org PhysicsNon-adiabatic ponderomotive effects in photoemission from nanotips in intense mid-infrared laser fields. (arXiv:1905.06079v1 [physics.optics])

Transient near-fields around metallic nanotips drive many applications, including the generation of ultrafast electron pulses and their use in electron microscopy. We have investigated the electron emission from a gold nanotip driven by mid-infrared few-cycle laser pulses. We identify a low-energy peak in the kinetic energy spectrum and study its shift to higher energies with increasing laser intensities from $1.7$ to $3.7\cdot10^{11} \mathrm{W}/\mathrm{cm}^2$. The experimental observation of the upshift of the low-energy peak is compared to a simple model and numerical simulations, which show that the decay of the near-field on a nanometer scale results in non-adiabatic transfer of the ponderomotive potential to the kinetic energy of emitted electrons and in turn to a shift of the peak. We derive an analytic expression for the non-adiabatic ponderomotive shift, which, after the previously

05:35 Arxiv.org PhysicsVibrational Stark Spectroscopy on Fluorobenzene with Quantum Cascade Laser Dual Frequency Combs. (arXiv:1905.05758v1 [physics.chem-ph])

We demonstrate the performance of a dual frequency comb QCL spectrometer for the application of vibrational Stark spectroscopy. Measurements performed on fluorobenzene with the dual-comb spectrometer were compared to results obtained using a conventional Fourier transform infrared (FTIR) instrument in terms of spectral response, parameter estimation, and signal-to-noise ratio. The dual-comb spectrometer provided the same qualitative and quantitative data as the FTIR setup with an up to 9 or 52 times improved signal to noise ratio (SNR) in the current configuration when comparing against experimental or acquisition times, respectively. This improvement was made possible by the shorter experimental and acquisition times, and the brighter light-source. Additional characteristics of the dual-comb spectrometer applicable to vibrational Stark spectroscopy and their scaling properties for future

15.05.2019
16:43 RFI.frEiffel Tower in laser and strobe light show for 130th birthday

Paris’s iconic Eiffel Tower prepared to celebrate the 130th anniversary of its opening on Wednesday by welcoming 1,300 children before hosting a concert and an unprecedented sound and light show.

10:22 Technology.orgLaser trucks help maintain roads

Pavement engineering company, Dynatest, has developed a truck in partnership with DTU which analyses the state of the road

08:07 Arxiv.org PhysicsPulses from a mid-infrared quantum cascade laser frequency comb using an external compressor. (arXiv:1905.05672v1 [physics.optics])

A Martinez-type stretcher-compressor is used to modify the spectral phases of a high-power (~1 W) QCL comb emitted at 8.2 {\mu}m with more than 100 cm-1 spectral bandwidth. Using this scheme, we demonstrate a compression of the QCL output from a 134 ps continuous wave waveform, to a train of pulses of width 12 ps, and a power with peak to average ratio of 40.7. An evaluation of the phase noise of the free-running device yields an integrated timing jitter of 335 fs over the frequency range 20 kHz - 100 MHz, and a pulse-to-pulse jitter of 2.0 fs.

08:07 Arxiv.org PhysicsTerahertz Laser Combs in Graphene Field-Effect Transistors. (arXiv:1905.05536v1 [cond-mat.mes-hall])

Electrically injected terahertz (THz) radiation sources are extremely appealing given their versatility and miniaturization potential, opening the venue for integrated-circuit THz technology. In this work, we show that coherent THz frequency combs in the range $0.5~\mathrm{THz}<\omega/2\pi<10~\mathrm{THz}$ can be generated making use of graphene plasmonics. Our setup consists of a graphene field-effect transistor with asymmetric boundary conditions, with the radiation originating from a plasmonic instability that can be controlled by direct current injection. We put forward a combined analytical and numerical analysis of the graphene plasma hydrodynamics, showing that the instability can be experimentally controlled by the applied gate voltage and the injected current. Our calculations indicate that the emitted THz comb exhibits appreciable temporal coherence ($g^{(1)}(\tau)>0.6$)

08:07 Arxiv.org PhysicsDielectric-laser electron acceleration in a dual pillar grating with a distributed Bragg reflector. (arXiv:1905.05489v1 [physics.acc-ph])

We report on the efficacy of a novel design for dielectric laser accelerators by adding a distributed Bragg reflector (DBR) to a dual pillar grating accelerating structure. This mimics a double-sided laser illumination, resulting in an enhanced longitudinal electric field while reducing the deflecting transverse effects, when compared to single-sided illumination. We improve the coupling efficiency of the incident electric field into the accelerating mode by 57 percent. The 12 $\mu$m long structures accelerate sub-relativistic 28 keV electrons with gradients of up to 200 MeV/m in theory and 133 MeV/m in practice. Our work shows how lithographically produced nano-structures help to make novel laser accelerators more efficient.

06:55 Arxiv.org CSLASER: Lightweight And SEcure Remote keyless entry protocol (Extended version). (arXiv:1905.05694v1 [cs.CR])

Since Remote Keyless Entry (RKE) systems started to be widely used, several vulnerabilities in their protocols have been found. Attacks such as jamming-and-replay attacks and relay attacks are still effective against most recent RKE systems, even when many secure schemes have been designed. Although they are interesting from a theoretical point of view, the complexity of these solutions is excessive to implement them into a fob. This paper presents a lightweight and general solution based on a one message protocol, which guarantees the integrity and validity of the authentication in RKE systems, protecting the communication against the well-known jamming-and-replay and relay attacks, without using complex cryptographic schemes. Moreover, we also adapt our protocol for passive RKE (PRKE) systems. Our solution also includes a novel frequency-hopping-based approach which mitigates

14.05.2019
15:08 Phys.orgLaser-based technology helps doctors image full eye in 3-D

It is estimated that in 2015, 217 million people had moderate to severe vision impairment, while 36 million were blind, according to an article in the journal The Lancet Global Health. The World Health Organization predicts that about 80 % of vision impairment globally is preventable or curable. Early diagnosis is crucial for effective interventions.

10:48 Arxiv.org PhysicsBallistic Injection and Acceleration of Positrons in the Laser-Plasma Bubble Regime. (arXiv:1905.05096v1 [physics.plasm-ph])

A novel approach for positron injection and acceleration in laser driven plasma wakefield is proposed. A theoretical model is developed and confirmed through simulations. The proposal is based on employing two co-axially propagating beams ring-shaped and Gaussian beams to drive wakefields in a preformed plasma volume filled with both electrons and positrons.The laser's ponderomotive force is utilized to provide the transverse momenta for positron injection and those positrons can be trapped by the focusing field and then accelerated by the wake wave. The simulation shows that a relatively high-charge, quasi-monoenergetic positrons beams can be achieved. The positrons are accelerated to more than 200 MeV within 2mm, which is similar to the acceleration of electrons in the same scenario, with the same normalized peak laser intensities of $a=2$ for both Gaussian and ring-shaped

10:48 Arxiv.org PhysicsComment on "Retrieval of phase relation and emission profile of quantum cascade laser frequency combs''. (arXiv:1905.04980v1 [physics.optics])

A recent publication on arXiv:1905.00668 suggests that the phase relationship within a frequency comb can be reconstructed from a heterodyne measurement using a reference comb. In principle, following this approach, such retrieval of optical phases appears possible, but should give rise to a temporally constant signal. Instead, arXiv:1905.00668 provides experimental evidence for a pronounced relative drift of the phases, which indicates that the modes of the comb are not coherently phase-locked. This temporal drift can be explained if the comb under test is not equidistant. This further means that the underlying temporal waveform is not repetitive and cannot be compressed into a coherent short pulse. This artifact severely hampers suggested applications of quantum cascade lasers in precision metrology. Moreover, the notion of designating multi-mode quantum cascade lasers as frequency combs

10:48 Arxiv.org PhysicsSimilarity of magnetized plasma wake channels behind relativistic laser pulses with different wavelengths. (arXiv:1905.04932v1 [physics.plasm-ph])

Using particle-in-cell simulations of relativistic laser plasma wakes in the presence of an external magnetic field, we demonstrate that there exists a parameter window where the dynamics of the magnetized wake channel are largely independent of the laser wavelength $\lambda_{\rm las}$. One condition for this manifestation of "limited similarity" is that the electron density $n_{\rm e}$ is highly subcritical, so that the plasma does not affect the laser. The freedom to choose a convenient laser wavelength can be useful in experiments and simulations. In simulations, an up-scaled wavelength (and, thus, a coarser mesh and larger time steps) reduces the computational effort, while limited similarity ensures that the overall structure and evolutionary phases of the wake channel are preserved. In our demonstrative example, we begin with a terrawatt$\cdot$picosecond pulse from a ${\rm CO}_2$ laser

10:48 Arxiv.org PhysicsComputational Doppler-limited dual-comb spectroscopy with a free-running all-fiber laser. (arXiv:1905.04647v1 [physics.ins-det])

Dual-comb spectroscopy has emerged as an indispensable analytical technique in applications that require high resolution and broadband coverage within short acquisition times. Its experimental realization, however, remains hampered by intricate experimental setups with large power consumption. Here, we demonstrate an ultra-simple free-running dual-comb spectrometer realized in a single all-fiber cavity suitable for the most demanding Doppler-limited measurements. Our dual-comb laser utilizes just a few basic fiber components, allows to tailor the repetition rate difference, and requires only 350 mW of electrical power for sustained operation over a dozen of hours. As a demonstration, we measure low-pressure hydrogen cyanide within 1.7 THz bandwidth, and obtain better than 1% precision over a terahertz in 200 ms enabled by a drastically simplified all-computational phase correction algorithm.

10.05.2019
14:07 Phys.orgCopper oxide photocathodes: Laser experiment reveals location of efficiency loss

Solar cells and photocathodes made of copper oxide could theoretically attain high efficiencies for solar energy conversion. In practice, however, large losses occur. Now, a team at the HZB has been able to use a sophisticated femtosecond laser experiment to determine where these losses take place—not so much at the interfaces, but instead, far more in the interior of the crystalline material. These results provide indications on how to improve copper oxide and other metal oxides for applications such as energy materials.

06:56 Arxiv.org PhysicsElectrically pumped semiconductor laser with low spatial coherence and directional emission. (arXiv:1905.03671v1 [physics.optics])

We design and fabricate an on-chip laser source that produces a directional beam with low spatial coherence. The lasing modes are based on the axial orbit in a stable cavity and have good directionality. To reduce the spatial coherence of emission, the number of transverse lasing modes is maximized by fine-tuning the cavity geometry. Decoherence is reached in a few nanoseconds. Such rapid decoherence will facilitate applications in ultrafast speckle-free full-field imaging.

06:56 Arxiv.org PhysicsMultiple orbital effects in laser-induced electron diffraction of aligned molecules. (arXiv:1905.03596v1 [physics.chem-ph])

Photoelectron Angular Distributions (PADs) resulting from 800 nm and 1300 nm strong field ionization of impulsively aligned CF$_3$I molecules were analyzed using time-dependent density functional theory (TDDFT). The normalized difference between the PADs for aligned and anti-aligned molecules displays large modulations in the high-energy re-collision plateau that are assigned to the diffraction of back-scattered photoelectrons. The TDDFT calculations reveal that, in spite of their 2.6 eV energy difference, ionization from the HOMO-1 orbital contributes to the diffraction pattern on the same footing as ionization from the doubly degenerate HOMO orbital.

06:56 Arxiv.org PhysicsAtomic-resolution imaging of carbonyl sulfide by laser-induced electron diffraction. (arXiv:1905.03541v1 [physics.chem-ph])

Measurements on the strong-field ionization of carbonyl sulfide molecules by short, intense, 2~\um wavelength laser pulses are presented from experiments where angle-resolved photoelectron distributions were recorded with a high-energy velocity map imaging spectrometer, designed to reach a maximum kinetic energy of 500~eV. The laser-field-free elastic-scattering cross section of carbonyl sulfide was extracted from the measurements and is found in good agreement with previous experiments, performed using conventional electron diffraction. By comparing our measurements to the results of calculations, based on the quantitative rescattering theory (QRS), the bond lengths and molecular geometry were extracted from the experimental differential cross sections to a precision better than $\pm5$~pm and in agreement with the known values.

01:58 ScienceDaily.comCopper oxide photocathodes: Laser experiment reveals location of efficiency loss

Solar cells and photocathodes made of copper oxide might in theory attain high efficiencies for solar energy conversion. In practice, however, large losses occur. Now researchers has been able to use a sophisticated femtosecond laser experiment to determine where these losses take place: not so much at the interfaces, but instead far more in the interior of the crystalline material. These results provide indications on how to improve copper oxide and other metal oxides for applications as energy materials.

09.05.2019
09:45 Arxiv.org PhysicsExtremely elastic soliton crystals generated in a passively mode-locked tunable high-repetition-rate fiber laser. (arXiv:1905.03129v1 [physics.optics])

We present the first direct observation of the bound state of multiple dissipative optical solitons in which bond length and bond strength can be individually controlled in a broad range in a regular manner. We have observed experimentally a new type of stable and extremely elastic soliton crystals that can be stretched and compressed many times conserving their structure by adjusting the bond properties in real time in a specially designed passively mode-locked fiber laser incorporating highly asymmetric tunable Mach-Zehnder interferometer. The temporal structure and dynamics of the generated soliton crystals have been studied using an asynchronous optical sampling system with picosecond resolution. We demonstrated that stable and robust soliton crystal can be formed by two types of primitive structures: single dissipative solitons, and(or) pairs of dissipative soliton and pulse with lower

08.05.2019
20:51 WhatReallyHappened.comClassified Air Force Laser Weapon For Stealth Jets Shoots Down Missiles

The Air Force Research Laboratory (AFRL) Self-Protect High Energy Laser Demonstrator (SHiELD) Advanced Technology Demonstration (ATD) Program, has completed a series of tests last month that successfully shot down "several" missiles with a ground-based laser.
The field training exercise occurred on April 23 at the White Sands Missile Range in New Mexico, reported the 88th Air Base Wing Public Affairs.
The SHiELD program has developed a directed energy weapon that will eventually be molded into an aircraft pod. Fifth-generation fighter jets and drones will soon have the ability to destroy surface-to-air (SAM) and air-to-air (AAM) missiles with laser beams.
"This critical demonstration shows that our directed energy systems are on track to be a game changer for our warfighters," said Dr. Kelly Hammett, director of AFRL’s Directed Energy Directorate.

05:30 Arxiv.org PhysicsA perturbative approach to self-phase modulation and self-steepening of short laser pulses propagating in nonlinear media. (arXiv:1905.02252v1 [physics.optics])

The solution of the wave equation in the envelope approximation with temporal corrections for a laser pulse propagating in a medium where the Kerr effect, field ionization, and associated absorption take place, is obtained through a first-order perturbative approach. The closed-form expressions so obtained clarify the influence of the various terms of the equation on the laser amplitude and on the frequency generation as a function of the retarded time. Furthermore, they allow extracting scaling parameters which size the nonlinear effects. The results are illustrated quantitatively on the case of a femtosecond pulse focused in the air with typical parameters.

05:30 Arxiv.org PhysicsMinimizing betatron coupling of energy spread and divergence in laser-wakefield accelerated electron beams. (arXiv:1905.02240v1 [physics.acc-ph])

Matched beam loading in laser wakefield acceleration (LWFA), characterizing the state of flattening of the acceleration electric field along the bunch, leads to the minimization of energy spread at high bunch charges. Here, we demonstrate by independently controlling injected charge and acceleration gradients, using the self-truncated ionization injection scheme, that minimal energy spread coincides with a reduction of the normalized beam divergence. With the simultaneous confirmation of a constant beam radius at the plasma exit, deduced from betatron radiation spectroscopy, we attribute this effect to the reduction of chromatic betatron decoherence. Thus, beam loaded LWFA enables highest longitudinal and transverse phase space densities.

07.05.2019
08:15 Arxiv.org PhysicsStrong energy enhancement in a laser-driven plasma-based accelerator through stochastic friction. (arXiv:1905.02152v1 [physics.acc-ph])

Conventionally, friction is understood as an efficient dissipation mechanism depleting a physical system of energy as an unavoidable feature of any realistic device involving moving parts, e.g., in mechanical brakes. In this work, we demonstrate that this intuitive picture loses validity in nonlinear quantum electrodynamics, exemplified in a scenario where spatially random friction counter-intuitively results in a highly directional energy flow. This peculiar behavior is caused by radiation friction, i.e., the energy loss of an accelerated charge due to the emission of radiation. We demonstrate analytically and numerically how radiation friction can enhance the performance of a specific class of laser-driven particle accelerators. We find the unexpected directional energy boost to be due to the particles' energy being reduced through friction whence the driving laser can accelerate them more

08:15 Arxiv.org PhysicsWakefield Excited by Ultrashort Laser Pulses in Near-Critical Density Plasmas. (arXiv:1905.02043v1 [physics.plasm-ph])

Laser wakefield acceleration (LWFA) using high repetition rate mJ-class laser systems brings unique opportunities for a broad range of applications. In order to meet the conditions required for the electron acceleration with lasers operating at lower energies, one has to use high density plasmas and ultrashort pulses. In the case of a few-cycle pulse, the dispersion and the carrier envelope phase effects can no longer be neglected. In this work, the properties of the wake waves generated by ultrashort pulse lasers in near-critical density plasmas are investigated. The results obtained may lead to enhancement of the quality of LWFA electron beams using kHz laser systems.

08:15 Arxiv.org PhysicsOptimized Er/Yb fiber laser. (arXiv:1905.01952v1 [physics.optics])

We measure the output power of an Er/Yb fiber laser with twelve different SMF-28 narrowband output couplers and demonstrate experimentally that the optimal reflectivity is ~ 1 %. The fiber laser efficiency with the optimal output coupler is ~ 38 %. In addition, we successfully inscribe a similar output coupler in-situ during laser operation with 800 nm femtosecond pulses and the phase mask technique. An output power very close to the optimal was obtained with the in-situ inscribed output coupler.

08:15 Arxiv.org PhysicsNumerical Contribution of Micro-Pulsed Laser Effect on Copper. (arXiv:1905.01938v1 [physics.comp-ph])

A numerical model is developed to study heat, fluid flow and radiation transfers during the interaction between a UV laser beam and copper. Calculations are performed for a laser of Gaussian and Lorentzian shapes of a wavelength of 400nm, a focal spot radius of 50 micrometers and duration of 80 microsec. In order to describe the transient behaviour in and above the copper target, heat and Navier-Stokes equations are linked to Lambert Beer relationship by taking into account the conduction, and the convection phenomena. The resulting equations are schemed by the finite element method. Comparison with the literature showed qualitative and quantitative agreements for Crater depths and transmission profiles for different laser pulse numbers. Then, the effects of the laser fluences, the Gaussian and Lorentzian shapes on temperature, velocities, melting and evaporation phenomena are

08:15 Arxiv.org PhysicsThomson backscattering in combined two laser and magnetic field. (arXiv:1905.01645v1 [physics.optics])

The Thomson backscattering of an electron moving in combined fields is studied by a dynamically assisted mechanism. The combined fields are composed of two co-propagating laser fields and a magnetic field, where the first laser field is strong and low-frequency while the second is weak and high-frequency, relatively. The dependence of fundamental frequency of emission on the ratio of incident laser high-to-low frequency is presented and the spectrum of backscattering is obtained. It is found that, with a magnetic field, the peak of the spectrum and the corresponding radiation frequency are significantly larger in case of two-laser than that in case of only one laser. They are also improved obviously as the frequency of the weak laser field. Another finding is the nonlinear correlation between the emission intensity of the backscattering and the intensity of the weak laser field. These results

06.05.2019
22:01 ExtremeTech.comMassive 10-Petawatt Laser Can Vaporize Matter

The most powerful laser ever made has one-tenth the power of the sun and is being used in cancer therapy research. P.S. It works.
The post Massive 10-Petawatt Laser Can Vaporize Matter appeared first on ExtremeTech.

03.05.2019
14:42 Phys.orgLaser-driven spin dynamics in ferrimagnets: How does the angular momentum flow?

When exposed to intense laser pulses, the magnetization of a material can be manipulated very fast. Fundamentally, magnetization is connected to the angular momentum of the electrons in the material. A team of researchers led by scientists from the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) has now been able to follow the flow of angular momentum during ultrafast optical demagnetization in a ferrimagnetic iron-gadolinium alloy in great detail, in order to understand the fundamental processes and their speed limits. The results were published in Physical Review Letters.

05:32 ScienceDaily.comResearch sparks new insights on laser welding

Researchers discuss an ambitious project to understand the basic principles of laser welding better than ever before.

04:51 Arxiv.org PhysicsParticle-in-Cell Simulations of Density Peak Formation and Ion Acceleration from Short Pulse Laser-Driven Ponderomotive Steepening. (arXiv:1905.00888v1 [physics.plasm-ph])

We use particle-in-cell (PIC) simulations and simple analytic models to investigate the laser-plasma interaction known as ponderomotive steepening. When normally incident laser light reflects at the critical surface of a plasma, the resulting standing electromagnetic wave modifies the electron density profile via the ponderomotive force, which creates peaks in the electron density separated by approximately half of the laser wavelength. What is less well studied is how this charge imbalance accelerates ions towards the electron density peaks, modifying the ion density profile of the plasma. Idealized PIC simulations with an extended underdense plasma shelf are used to isolate the dynamics of ion density peak growth for a 42 fs pulse from an 800 nm laser with an intensity of 10$^{18}$ W cm$^{-2}$. These simulations exhibit sustained longitudinal electric fields of 200 GV m$^{-1}$, which

04:51 Arxiv.org PhysicsExperimental evidence of laser power oscillations induced by the relative Fresnel (Goos-Haenchen) phase. (arXiv:1905.00862v1 [physics.optics])

The amplification of the relative Fresnel (Goos-Haenchen) phase by an appropriate number of total internal reflections and the choice of favorable incidence angles allow to observe full oscillations in the power of a DPSS laser transmitted through sequential BK7 blocks. The experimental results confirm the theoretical predictions. The optical apparatus used in this letter can be seen as a new type of two-phase ellipsometric system where the phase of the complex refractive index is replaced by the relative Fresnel (Goos-Haenchen) phase.

04:51 Arxiv.org PhysicsLaser source for dimensional metrology: investigation of an iodine stabilized system based on narrow linewidth 633 nm DBR diode. (arXiv:1905.00795v1 [physics.optics])

We demonstrated that an iodine stabilized Distributed Bragg Reflector (DBR) diode based laser system lasing at a wavelength in close proximity to $\lambda = 633\,$nm could be used as an alternative laser source to the He-Ne lasers in both scientific and industrial metrology. This yields additional advantages besides the optical frequency stability and coherence: inherent traceability, wider optical frequency tuning range, higher output power and high frequency modulation capability. We experimentally investigated the characteristics of the laser source in two major steps: first using a wavelength meter referenced to a frequency comb controlled with a hydrogen maser and then on a interferometric optical bench testbed where we compared the performance of the laser system with that of a traditional frequency stabilized He-Ne laser. The results indicate that DBR diode laser system provides a good

04:51 Arxiv.org PhysicsRetrieval of phase relation and emission profile of quantum cascade laser frequency combs. (arXiv:1905.00668v1 [physics.optics])

The major development recently undergone by quantum cascade lasers has effectively extended frequency comb emission to longer-wavelength spectral regions, i.e. the mid and far infrared. Unlike classical pulsed frequency combs, their mode-locking mechanism relies on four-wave mixing nonlinear processes, with a temporal intensity profile different from conventional short-pulses trains. Measuring the absolute phase pattern of the modes in these combs enables a thorough characterization of the onset of mode-locking in absence of short-pulses emission, as well as of the coherence properties. Here, by combining dual-comb multi-heterodyne detection with Fourier-transform analysis, we show how to simultaneously acquire and monitor over a wide range of timescales the phase pattern of a generic frequency comb. The technique is applied to characterize a mid-infrared and a terahertz quantum cascade laser

02.05.2019
17:38 ScienceDaily.comLaser-driven spin dynamics in ferrimagnets: How does the angular momentum flow?

A team of researchers has now been able to follow the flow of angular momentum during ultrafast optical demagnetization in a ferrimagnetic iron-gadolinium alloy in great detail, in order to understand the fundamental processes and their speed limits.

07:24 Arxiv.org PhysicsCoherently driving a single quantum two-level system with dichromatic laser pulses. (arXiv:1905.00275v1 [quant-ph])

Efficient excitation of a single two-level system usually requires that the driving field is at the same frequency as the atomic transition. However, the scattered laser light in solid-state implementations can dominate over the single photons, imposing an outstanding challenge to perfect single-photon sources. Here, we propose a background-free method using a phase-locked dichromatic electromagnetic field with no spectral overlap with the optical transition for a coherent control of a two-level system, and we demonstrate this method experimentally with a single quantum dot embedded in a micropillar. Single photons generated by pi excitation show a purity of 0.988(1) and indistinguishability of 0.962(6). Further, the phase-coherent nature of the two-color excitation is captured by the resonance-fluorescence intensity dependence on the relative phase between the two pulses. Our two-color

07:24 Arxiv.org PhysicsAccuracy of the semiclassical picture of photoionization in intense laser fields. (arXiv:1905.00213v1 [physics.atom-ph])

In the semiclassical picture of photoionization process in intense laser fields, the ionization rate solely depends on the amplitude of the electric field and the final photoelectron momentum corresponds to the instant of ionization of the photoelectron, however, this picture has never been checked rigorously. Recently an attosecond angular streaking technique based on this semiclassical perspective has been widely applied to temporal measurement of the atomic and molecular dynamics in intense laser fields. We use a Wigner-distribution-like function to calculate the time-emission angle distribution, angular distribution and ionization time distribution for atomic ionization process in elliptically polarized few-cycle laser fields. By comparing with semiclassical calculations, we find that the two methods always show discrepancies except in some specific cases and the offset angles are

00:07 Phys.orgResearch sparks new insights on laser welding

On its surface, the work is deceptively simple: Shoot a high-power laser beam onto a piece of metal for a fraction of a second and see what happens. But researchers say the physics of laser welding is surprisingly complex. A better understanding of the interaction between laser and metal could give industry more control over laser welding, a technology that is becoming increasingly popular in manufacturing.

01.05.2019
10:05 Arxiv.org PhysicsSpin-polarization effects of ultrarelativistic electron beam in ultraintense two-color laser pulses. (arXiv:1904.13246v1 [physics.plasm-ph])

Spin-polarization effects of an ultrarelativistic electron beam head-on colliding with ultraintense two-color laser pulses are investigated comprehensively in the quantum radiation-dominated regime. We employ a Monte Carlo method, derived from the recent work of [Phys. Rev. Lett. {\bm 122}, 154801 (2019)], to calculate the spin-resolved electron dynamics and photon emissions in the local constant field approximation. We find that electron radiation probabilities in adjacent half cycles of a two-color laser field are apparently asymmetric due to radiative spin effects, and consequently, after interaction the electron beam can have a total polarization of about 11\% and a partial polarization of up to about 63\%, with currently achievable laser facilities, which may be utilized in high-energy physics and nuclear physics. Moreover, the considered effects are shown to be robust with respect to

10:05 Arxiv.org PhysicsLaser-Plasma Interactions Enabled by Emerging Technologies. (arXiv:1904.13218v1 [physics.plasm-ph])

An overview from the past and an outlook for the future of fundamental laser-plasma interactions research enabled by emerging laser systems.

30.04.2019
14:55 Phys.orgAn atom in a cavity extracts highly pure single photons from weak laser light

Quantum physicists can now distil a kind of photon schnapps. When spirits are distilled, the alcohol content increases relative to the water content. A similar method developed by a team from the Max Planck Institute of Quantum Optics in Garching works on light quanta – photons. It extracts individual photons from a light source, pushes back the unwanted vacuum component, and reports this event. Such single photons are important quantum bits for the currently emerging quantum information technology.

05:32 Arxiv.org PhysicsDynamical diversity of pulsating solitons in a fiber laser. (arXiv:1904.12646v1 [physics.optics])

Pulsating behavior is a universal phenomenon in versatile fields. In nonlinear dissipative systems, the solitons could also pulsate under proper conditions and show many interesting dynamics. However, the pulsation dynamics is generally concerned with single soliton case. Herein, by utilizing real-time spectroscopy technique, namely, dispersive Fourier-transform (DFT), we reveal the versatile categories of pulsating solitons in a fiber laser. In particular, the weak to strong explosive behaviors of pulsating soliton, as well as the rogue wave generation during explosions were observed. Moreover, the concept of soliton pulsation was extended to the multi-soliton case. It is found that the simultaneous pulsation of energy, separation and relative phase difference could be observed for solitons inside the molecule, while the pulsations of each individual in multi-soliton bunch could be regular

05:32 Arxiv.org PhysicsUltrafast Polarization of an Electron Beam in an Intense Bi-chromatic Laser Field. (arXiv:1904.12037v1 [physics.plasm-ph])

Here, we demonstrate the radiative polarization of high-energy electron beams in collisions with ultrashort pulsed bi-chromatic laser fields. Employing a Boltzmann kinetic approach for the electron distribution allows us to simulate the beam polarization over a wide range of parameters and determine the optimum conditions for maximum radiative polarization. Those results are contrasted with a Monte-Carlo algorithm where photon emission and subsequent electron polarization is treated fully quantum mechanically using spin-dependent photon emission rates. The latter method includes realistic focusing laser fields, which allows us to simulate a near-term experimentally feasible scenario of a 8 GeV electron beam scattering from a 1 PW laser pulse and provide a measurement that would verify the ultrafast radiative polarization in high-intensity laser pulses that we predict. Aspects of spin

29.04.2019
08:55 GizmagWorld s first laser radio transmitter/receiver paves way for ultra-high-speed Wi-Fi

Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have, for the first time, used a semiconductor laser to send and receive radio signals. The hybrid electronic-photonic device uses a laser to extract and transmit microwave signals, providing a data rate that may one day lead to ultra-high-speed Wi-Fi.

08:10 Arxiv.org PhysicsComb-based WDM transmission at 10 Tbit/s using a DC-driven quantum-dash mode-locked laser diode. (arXiv:1904.11952v1 [eess.SP])

Chip-scale frequency comb generators have the potential to become key building blocks of compact wavelength-division multiplexing (WDM) transceivers in future metropolitan or campus-area networks. Among the various comb generator concepts, quantum-dash (QD) mode-locked laser diodes (MLLD) stand out as a particularly promising option, combining small footprint with simple operation by a DC current and offering flat broadband comb spectra. However, the data transmission performance achieved with QD-MLLD was so far limited by strong phase noise of the individual comb tones, restricting experiments to rather simple modulation formats such as quadrature phase shift keying (QPSK) or requiring hard-ware-based compensation schemes. Here we demonstrate that these limitations can be over-come by digital symbol-wise phase tracking algorithms, avoiding any hardware-based phase-noise compensation. We

08:10 Arxiv.org PhysicsA Microscale Nanosecond Time-resolved Platinum Thermometer Probing Gaussian Pulsed Laser Induced Temperature. (arXiv:1904.11879v1 [physics.ins-det])

Pulsed laser processing is playing a crucial role in additive manufacturing and nanomaterial processing. However, probing transient temperature during laser interaction with the processed materials is challenging with both high spatial and temporal resolution. Here, we demonstrate 9ns rise time 50{\mu}m sized Pt thin film sensor for probing the temperature field induced by a nanosecond pulsed laser on a semiconductor thin film. The error sources and associated improvements are discussed regarding the fabrication, sensor pattern and electrical circuits. We further carried out the first experimental and theoretical analysis of spatial resolution and accuracy for measuring gaussian pulse on the serpentine structure. Transparent silica and sapphire substrates, as well as 7-45nm insulation layer thickness, are compared for sensing accuracy and temporal resolution. Lastly, the measured absolute

26.04.2019
16:44 CNNNFL draft: 24-7 frenzy as 'war rooms' laser in on hottest talent

The 84th version of the NFL draft looks almost nothing like the original, when it centered around 90 names on a chalkboard in a hotel.

25.04.2019
19:37 ScienceDaily.comThe first laser radio transmitter

For the first time, researchers have used a laser as a radio transmitter and receiver, paving the way for towards ultra-high-speed Wi-Fi and new types of hybrid electronic-photonic devices.

18:06 Phys.orgResearchers transmit data via a semiconductor laser, opening the door to ultra-high-speed Wi-Fi

You've never heard Dean Martin like this.

03:54 ScienceDaily.comA breakthrough in the study of laser/plasma interactions

Researchers have developed a particle-in-cell simulation tool that is enabling cutting-edge simulations of laser/plasma coupling mechanisms. More detailed understanding of these mechanisms is critical to the development of ultra-compact particle accelerators and light sources that could solve long-standing challenges in medicine, industry, and fundamental science.

24.04.2019
22:43 Phys.orgA breakthrough in the study of laser/plasma interactions

A new 3-D particle-in-cell (PIC) simulation tool developed by researchers from Lawrence Berkeley National Laboratory and CEA Saclay is enabling cutting-edge simulations of laser/plasma coupling mechanisms that were previously out of reach of standard PIC codes used in plasma research. More detailed understanding of these mechanisms is critical to the development of ultra-compact particle accelerators and light sources that could solve long-standing challenges in medicine, industry, and fundamental science more efficiently and cost effectively.

19:17 ScienceDaily.comQuality of laser beam shaping can be enhanced at no extra cost

Researchers have developed a technique for improving accuracy of laser beam shaping and wavefront obtained by conventional methods with no additional cost by optimizing virtual phase grating.

17:03 Phys.orgQuality of laser beam shaping can be enhanced at no extra cost

Researchers from Osaka University have developed a technique for improving accuracy of laser beam shaping and wavefront obtained by conventional methods with no additional cost by optimizing virtual phase grating. The results of their research were published in Scientific Reports.

23.04.2019
09:36 Arxiv.org CSComplete Scene Reconstruction by Merging Images and Laser Scans. (arXiv:1904.09568v1 [cs.CV])

Image based modeling and laser scanning are two commonly used approaches in large-scale architectural scene reconstruction nowadays. In order to generate a complete scene reconstruction, an effective way is to completely cover the scene using ground and aerial images, supplemented by laser scanning on certain regions with low texture and complicated structure. Thus, the key issue is to accurately calibrate cameras and register laser scans in a unified framework. To this end, we proposed a three-step pipeline for complete scene reconstruction by merging images and laser scans. First, images are captured around the architecture in a multi-view and multi-scale way and are feed into a structure-from-motion (SfM) pipeline to generate SfM points. Then, based on the SfM result, the laser scanning locations are automatically planned by considering textural richness, structural complexity of the scene

22.04.2019
06:04 Arxiv.org PhysicsEffects of hole-boring and relativistic transparency on particle acceleration in overdense plasma irradiated by short multi-PW laser pulses. (arXiv:1904.09057v1 [physics.plasm-ph])

Propagation of short and ultra-intense laser pulses in a semi-infinite space of overdense hydrogen plasma is analyzed via fully-relativistic, real geometry particle-in-cell (PIC) simulations including radiation friction. The relativistic transparency and hole-boring regimes are found to be sensitive to the transverse plasma field, backward light reflection, and laser pulse filamentation. For laser intensities approaching $I\sim10^{24}$ W/cm$^2$ the direct laser acceleration of protons, along with ion Coulomb explosion, results in their injection into the acceleration phase of the compressed electron wave at the front of the laser pulses. The protons are observed to be accelerated up to 10-20 GeV with densities around a few times the critical density. The effect strongly depends on initial density and laser intensity disappearing with initial density increase and intensity

02:02 TheStar.comLIVE: Raptors laser-focused ahead of Game 4 against Magic: ‘We don’t skip steps here’

ORLANDO, FLA.—There is a job for the Raptors to do and as much as some fans are already looking ahead to a second-round NBA playoff series, the Toronto players are too wise to do that.
“We don’t skip steps here,” Danny Green said Sunday, hours before the Raptors and Orlando Magic met in Game 4 of their series here. “We can’t think about the next series, we haven’t won this series yet. Orlando is our focus, they deserve our focus, they’re a pretty damn good team and we’re not looking ahead, we haven’t beat them yet, the job is not finished.”
The Raptors are up 2-1 in the best-of-seven series with Game 5 in Toronto on Tuesday. The winner of this series meets with Philadelphia or Brooklyn in the next round, the Sixers lead that series 3-1.
The only snippet of “news” going into the game was that Kawhi Leonard was feeling better after fighting a bug through Game 3.
“Just some

19.04.2019
06:44 Arxiv.org PhysicsMagnetic field generation from a coil-shaped foil by a laser-triggered hot-electron current. (arXiv:1904.08673v1 [physics.plasm-ph])

A strong electron current triggered by a femtosecond relativistically intense laser pulse in a foil coil-like target is shown to be able to generate a solenoidal-type extremely strong magnetic field. The magnetic field lifetime sufficiently exceeds the laser pulse duration and is defined mainly by the target properties. The process of the magnetic field generation was studied with 3D PIC simulations. It is demonstrated that the pulse and the target parameters allow controlling the field strength and duration. The scheme studied is of great importance for laser-based magnetization technologies.

06:44 Arxiv.org PhysicsSpatiotemporal self-similar fiber laser. (arXiv:1904.08456v1 [physics.optics])

In this Letter, we demonstrate, to the best of our knowledge, the first spatiotemporally mode-locked fiber laser with self-similar pulse evolution. The multimode fiber oscillator generates parabolic amplifier similaritons at 1030 nm with 90 mW average power, 2.3 ps duration, and 37.9 MHz repetition rate. Remarkably, we observe experimentally a near-Gaussian beam quality (M^2<1.4) at the output of the highly multimode fiber. The output pulses are compressed to 192 fs via an external grating compressor. Numerical simulations are performed to investigate the cavity dynamics which confirm experimental observations of self-similar pulse propagation. The reported results open a new direction to investigate new types of pulse besides beam shaping and nonlinear dynamics in spatiotemporal mode-locked fiber lasers.

18.04.2019
21:19 WhatReallyHappened.comChina Tests Tactical Laser Similar to US Navy System

15:42 News-Medical.NetSynergy™ Neo2 Now Available with TRF Laser

BioTek’s Synergy™ Neo2 Multi-Mode Microplate Reader offers even more powerful performance and assay flexibility for screening and core laboratories with an optional TRF laser.

09:28 Arxiv.org PhysicsThree-dimensional femtosecond laser nanolithography of crystals. (arXiv:1904.08264v1 [physics.optics])

Nanostructuring hard optical crystals has so far been exclusively feasible at their surface, as stress induced crack formation and propagation has rendered high precision volume processes ineffective. We show that the inner chemical etching reactivity of a crystal can be enhanced at the nanoscale by more than five orders of magnitude by means of direct laser writing. The process allows to produce cm-scale arbitrary three-dimensional nanostructures with 100 nm feature sizes inside large crystals in absence of brittle fracture. To showcase the unique potential of the technique, we fabricate photonic structures such as sub-wavelength diffraction gratings and nanostructured optical waveguides capable of sustaining sub-wavelength propagating modes inside yttrium aluminum garnet crystals. This technique could enable the transfer of concepts from nanophotonics to the fields of solid state lasers and

09:28 Arxiv.org PhysicsCoherent diffraction radiation of relativistic terahertz pulses from a laser-driven micro-plasma-waveguide. (arXiv:1904.07914v1 [physics.plasm-ph])

We propose a method to generate isolated relativistic terahertz (THz) pulses using a high-power laser irradiating a mirco-plasma-waveguide (MPW). When the laser pulse enters the MPW, high-charge electron bunches are produced and accelerated to ~ 100 MeV by the transverse magnetic modes. A substantial part of the electron energy is transferred to THz emission through coherent diffraction radiation as the electron bunches exit the MPW. We demonstrate this process with three-dimensional particle-in-cell simulations. The frequency of the radiation is determined by the incident laser duration, and the radiated energy is found to be strongly correlated to the charge of the electron bunches, which can be controlled by the laser intensity and micro-engineering of the MPW target. Our simulations indicate that 100-mJ level relativistic-intense THz pulses with tunable frequency can be generated at

17.04.2019
05:06 Arxiv.org PhysicsReal-time monitoring via second-harmonic interferometry of a flow gas cell for laser wakefield acceleration. (arXiv:1904.07669v1 [physics.optics])

The use of a gas cell as a target for laser weakfield acceleration (LWFA) offers the possibility to obtain stable and manageable laser-plasma interaction process, a mandatory condition for practical applications of this emerging technique, especially in multi-stage accelerators. In order to obtain full control of the gas particle number density in the interaction region, thus allowing for a long term stable and manageable LWFA, real-time monitoring is necessary. In fact, the ideal gas law cannot be used to estimate the particle density inside the flow cell based on the preset backing pressure and the room temperature because the gas flow depends on several factors like tubing, regulators and valves in the gas supply system, as well as vacuum chamber volume and vacuum pump speed/throughput. Here, second-harmonic interferometry is applied to measure the particle number density inside a flow gas

04:20 Arxiv.org CSSpeed and Separation Monitoring using on-robot Time--of--Flight laser--ranging sensor arrays. (arXiv:1904.07379v1 [cs.RO])

In this paper, a speed and separation monitoring (SSM) based safety controller using three time-of-flight ranging sensor arrays fastened to the robot links, is implemented. Based on the human-robot minimum distance and their relative velocities, a controller output characterized by a modulating robot operation speed is obtained. To avert self-avoidance, a self occlusion detection method is implemented using ray-casting technique to filter out the distance values associated with the robot-self and the restricted robot workspace. For validation, the robot workspace is monitored using a motion capture setup to create a digital twin of the human and robot. This setup is used to compare the safety,performance and productivity of various versions of SSM safety configurations based on minimum distance between human and robot calculated using on-robot Time-of-Flight sensors, motion capture and a 2D

16.04.2019
22:30 ScienceDaily.comNew form of laser for sound

The optical laser has grown to a $10 billion global technology market since it was invented in 1960, and has led to Nobel prizes for Art Ashkin for developing optical tweezing and Gerard Mourou and Donna Strickland for work with pulsed lasers. Now scientists have created a different kind of laser -- a laser for sound, using the optical tweezer technique invented by Ashkin. 22:00 Phys.orgNew phonon laser could lead to breakthroughs in sensing and information processing The optical laser has grown to a$10 billion global technology market since it was invented in 1960, and has led to Nobel prizes for Art Ashkin for developing optical tweezing and Gerard Mourou and Donna Strickland for work with pulsed lasers. Now a Rochester Institute of Technology researcher has teamed up with experts at the University of Rochester to create a different kind of laser—a laser for sound, using the optical tweezer technique invented by Ashkin.

19:51 GizmagLaser-heated bubbles may find use in better, less painful tattooing

Getting a tattoo certainly isn't known for being a comfortable process. It can also cause damage to the skin, plus it results in bio-hazardous used needles that need to be properly disposed of. A new needle-free technique, however, gets around all of those problems.
.. Continue Reading Laser-heated bubbles may find use in better, less painful tattooing Category: Health & Wellbeing Tags: Laser Tattoo University of Twente

17:49 ExtremeTech.comYou Can Help NASA’s Laser-Scanning Satellite By Measuring Trees With Your Phone

ICESat-2 measures elevation from orbit as part of NASA's climate research, but the agency would like some data from the ground to verify those readings. So, it's rolled out a new tool in the GLOBE Observer app for iPhone and Android.
The post You Can Help NASA’s Laser-Scanning Satellite By Measuring Trees With Your Phone appeared first on ExtremeTech.

17:48 RT.com‘Assassin’s Creed Unity’ & art historian’s laser scans may prove critical to Notre Dame restoration

As France and the wider world mourns the blaze that gutted the iconic Notre Dame Cathedral, speculation is growing online that help in rebuilding the national treasure may come from the unlikeliest of places: a video game. Read Full Article at RT.com

07:38 Arxiv.org PhysicsFirst experiments on Revolver shell collisions at the OMEGA Laser. (arXiv:1904.07086v1 [physics.plasm-ph])

Results of recent experiments on the OMEGA Laser are presented, demonstrating the ablator-driver shell collision relevant to the outer two shells of the Revolver triple-shell inertial-confinement-fusion concept [K. Molvig et al., PRL~{\bf 116}, 255003 (2016)]. These nested two-shell experiments measured the pre- and post-collision outer-surface trajectory of the 7.19 g/cc chromium inner shell. Measurements of the shell trajectory are in excellent agreement with simulations; the measured outer-surface velocity was $7.52\pm0.59$ cm/$\mu$s compared to the simulated value of 7.27 cm/$\mu$s. Agreement between the measurements and simulations provides confidence in our ability to model collisions with features which have not been validated previously. Notable features include the absence of $\sim$40 mg/cc foam between shells commonly used in double shell experiments, a dense (7.19 g/cc) inner shell

07:38 Arxiv.org PhysicsAttosecond Pulse Amplification in a Plasma-Based X-Ray Laser Dressed by an Infrared Laser Field. (arXiv:1904.07034v1 [physics.optics])

We suggest a technique to amplify a train of attosecond pulses, produced by high-harmonic generation (HHG) of an infrared (IR) laser field, in an active medium of a plasma-based X-ray laser. This technique is based on modulation of transition frequency of the X-ray laser by the same IR field, as used to generate the harmonics, via linear Stark effect, which results in redistribution of the resonant gain and simultaneous amplification of a wide set of harmonics in the incident field. We propose an experimental implementation of the suggested technique in active medium of C5+ ions at wavelength 3.4 nm in the "water window" range and show the possibility to amplify by two orders of magnitude a train of attosecond pulses with pulse duration down to 100 as. We show also a possibility to isolate a single attosecond pulse from the incident attosecond pulse train during its amplification in optically

07:38 Arxiv.org PhysicsHV discharges triggered by dual- and triple-frequency laser filaments. (arXiv:1904.07030v1 [physics.plasm-ph])

We study the use of frequency upconversion schemes of near-IR picosecond laser pulses and compare their ability to guide and trigger electric discharges through filamentation in air. Upconversion, such as Second Harmonic Generation, is favorable for triggering electric discharges for given amount of available laser energy, even taking into account the losses inherent to frequency conversion. We focus on the practical question of optimizing the use of energy from a given available laser system and the potential advantage to use frequency conversion schemes.

15.04.2019
18:46 ScienceDaily.comLaser processing method to increase efficiency of optoelectronic devices

Researchers discover new method to passivate defects in next generation optical materials.

17:20 Nanowerk.comNovel laser processing method to increase efficiency of optoelectronic devices

Scientists have discovered a new method to passivate defects in next generation optical materials to improve optical quality and enable the miniaturization of light emitting diodes and other optical elements.

17:20 Phys.orgTeam develops laser processing method to increase efficiency of optoelectronic devices

Scientists at the U.S. Naval Research Laboratory (NRL) discovered a new method to passivate defects in next generation optical materials to improve optical quality and enable the miniaturization of light emitting diodes and other optical elements.

12.04.2019
04:17 Arxiv.org PhysicsGeneration of nanoparticles of phtalocyanines by laser fragmentation and their interaction with gold nanoparticles. (arXiv:1904.05740v1 [physics.gen-ph])

Optical properties and morphology of laser generated Aluminum and Copper phthalocyanine nanoparticles (nAlPc and nCuPc) in water are experimentally studied. Near infrared laser source of nanosecond pulse duration was used for fragmentation of Pc micro-powder suspended in H2O. Extinction spectra in the visible and near IR range of NPs colloidal solutions in MQ water were acquired by means of optical spectroscopy. The optical density of both nCuPc and nAlPc increases with laser fragmentation time. Transmission electron microscopy was used for characterization of nanoparticle morphology and size analysis. It is found that nCuPc are made of short (100 nm) rectangular bars interconnected at various angles with other bars. Similar experiments were carried out for a colloidal solution, which is a mixture of Au and AlPc nanoparticles. It turned out that Au NPs in presence of nAlPc form large

04:17 Arxiv.org PhysicsBoosted High Order Harmonics from Electron Density Singularity Formed at the Relativistic Laser Bow Wave. (arXiv:1904.05574v1 [physics.plasm-ph])

We demonstrate coherent hard electromagnetic radiation generation from reflection by the electron density singularity formed at the relativistic bow wave in laser plasma via particle-in-cell simulations. Wake and bow waves driven by an intense laser pulse form an electron density singularity at the laser pulse front where they join. A counter-propagating laser pulse is reflected at the electron density modulations moving with relativistic velocity. The reflected electromagnetic pulse is compressed and its frequency is upshifted. Its frequency spectrum contains relativistic harmonics of the driver pulse frequency generated at the bow wave front, all upshifted with the same factor as the fundamental mode of the incident light.

11.04.2019
06:49 Arxiv.org PhysicsHigh-energy bremsstrahlung on atoms in a laser field. (arXiv:1904.05094v1 [hep-ph])

The impact of a laser field on the process of photon radiation by an ultra-relativistic electron in an atomic field is investigated. The angular distribution and the spectrum of the radiated photon are derived. By means of the quasiclassical approximation, the obtained results are exact in the parameters of the laser field and the atomic field. It is shown that the impact of the laser field is significant even for fairly average values of the laser field parameters routinely achievable nowadays. Therefore, an experimental observation of the influence of the laser field on bremsstrahlung in the atomic field is a very feasible task.

06:49 Arxiv.org PhysicsAcoustic-optic Q-switched cavityless weak-feedback laser based on Nd:GdVO4 bounce geometry. (arXiv:1904.04967v1 [physics.optics])

An AOQ (acoustic-optic Q-switched) laser with cavityless weak-feedback configuration is demonstrated based on a Nd:GdVO4 bounce geometry. The laser can operate at a repetition up to 500 kHz with the output power above 4W. The pulse-width at 100 kHz reaches 5.2 ns, which is 4.3 times the round-trip time. A theory of Q-switched cavityless weak-feedback laser is proposed for the first time, to our best knowledge. This theory is very suitable for analyzing short pulses comparable to round-trip time. By utilizing the theory, simulation is implemented for our experimental conditions. The consistence between the simulation and the experimental results proves the validity of our theory.

06:49 Arxiv.org PhysicsEnhanced relativistic-electron beam collimation using two consecutive laser pulses. (arXiv:1904.04893v1 [physics.plasm-ph])

The double laser pulse approach to relativistic electron beam (REB) collimation has been investigated at the LULI-ELFIE facility. In this scheme, the magnetic field generated by the first laser-driven REB is used to guide a second delayed REB. We show how electron beam collimation can be controlled by properly adjusting laser parameters. By changing the ratio of focus size and the delay time between the two pulses we found a maximum of electron beam collimation clearly dependent on the focal spot size ratio of the two laser pulses and related to the magnetic field dynamics. Cu-K alpha and CTR imaging diagnostics were implemented to evaluate the collimation effects on the respectively low energy (< 100 keV) and high energy (> MeV) components of the REB.

10.04.2019
14:19 Phys.orgNASA demos CubeSat laser communications capability

Two NASA CubeSats teamed up on an impromptu optical, or laser, communications pointing experiment. The laser beam is seen as a brief flash of light close to the center of the focal plane, to the left of Earth's horizon.

09:17 Arxiv.org PhysicsUltrarelativistic polarized positron jets via collision of electron and ultraintense laser beams. (arXiv:1904.04305v1 [physics.plasm-ph])

Relativistic spin-polarized positron beams are indispensable for future electron-positron colliders to test modern high-energy physics theory with high precision. However, present techniques require very large scale facilities for those experiments.
We put forward a novel efficient way for generating ultrarelativistic polarized positron beams employing currently available laser fields. For this purpose the generation of polarized positrons via multiphoton Breit-Wheeler pair production and the associated spin dynamics in single-shot interaction of an ultraintense laser pulse with an ultrarelativistic electron beam is investigated in the quantum radiation-dominated regime. A specifically tailored small ellipticity of the laser field is shown to promote splitting of the polarized particles along the minor axis of laser polarization into two oppositely polarized beams. In spite of radiative

09:17 Arxiv.org PhysicsInfluence of laser spot size at diffuser plane on the longitudinal spatial coherence function of optical coherence microscopy system. (arXiv:1904.04245v1 [physics.optics])

Coherence properties and wavelength of light sources are indispensable for optical coherence microscopy/tomography as they greatly influence the signal to noise ratio, axial resolution, and penetration depth of the system. In the present letter, we investigated the longitudinal spatial coherence properties of the pseudo-thermal light source (PTS) as a function of spot size at the diffuser plane, which is controlled by translating microscope objective lens towards or away from the diffuser plane. The axial resolution of PTS is found to be maximum ~ 13 microns for the beam spot size of 3.5 mm at the diffuser plane. The change in the axial resolution of the system as the spot size is increased at the diffuser plane is further confirmed by performing experiments on standard gauge blocks of height difference of 15 microns. Thus, by appropriately choosing the beam spot size at the diffuser plane,

07:58 Technology.orgNASA Demos CubeSat Laser Communications Capability

Two NASA CubeSats teamed up on an impromptu optical, or laser, communications pointing experiment. The laser beam is

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