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# Laser

19.03.2019
19:06 Rejuvenation ResearchCombination of Grid Laser Photocoagulation and a Single Intravitreal Ranibizumab as an Efficient and Cost-Effective Treatment Option for Macular Edema Secondary to Branch Retinal Vein Occlusion

15:03 Phys.orgA laser technique proves effective to recover material designed to protect industrial products

Fluoropolymers are macromolecules made up of carbon and fluoride which, due to their properties, tend to be used as non-stick and anticorrosive coatings on a wide range of material. Products in the clothing, graphic, chemical and car industries as well as different metal molds and kitchen utensils need fluoropolymers for their coatings and to improve their features regarding sticking and resisting corrosion.

04:59 Arxiv.org PhysicsInteraction of carrier envelope phase-stable laser pulses with graphene: the transition from the weak-field to the strong-field regime. (arXiv:1903.07558v1 [physics.optics])

Ultrafast control of electron dynamics in solid state systems has recently found particular attention. By increasing the electric field strength of laser pulses, the light-matter interaction in solids might turn from a perturbative into a novel non-perturbative regime, where interband transitions from the valence to the conduction band become strongly affected by intraband motion. We have demonstrated experimentally and numerically that this combined dynamics can be controlled in graphene with the electric field waveform of phase-stabilized few-cycle laser pulses. Here we show new experimental data and matching simulation results at comparably low optical fields, which allows us to focus on the highly interesting transition regime where the light-matter interaction turns from perturbative to non-perturbative. We find a 5th order power-law scaling of the laser induced waveform-dependent

04:37 Arxiv.org MathLoss of phase and universality of stochastic interactions between laser beams. (arXiv:1705.01137v1 [physics.optics] CROSS LISTED)

We show that all laser beams gradually lose their initial phase information in nonlinear propagation. Therefore, if two beams travel a sufficiently long distance before interacting, it is not possible to predict whether they would intersect in- or out-of-phase. Hence, if the underlying propagation model is non-integrable, deterministic predictions and control of the interaction outcome become impossible. Because the relative phase between the two beams becomes uniformly distributed in $[0,2\pi]$, however, the statistics of the interaction outcome are universal, and can be efficiently computed using a polynomial-chaos approach, even when the distributions of the noise sources are unknown.

18.03.2019
21:38 ScienceDaily.comA laser technique proves effective to recover material designed to protect industrial products

The system has been validated for non-stick and anticorrosive coatings used in the manufacturing of a wide range of objects from car engines to kitchen utensils.

07:44 Arxiv.org PhysicsSpectral Control via Multi-Species Effects in PW-Class Laser-Ion Acceleration. (arXiv:1903.06428v1 [physics.plasm-ph])

Laser-ion acceleration with ultra-short pulse, PW-class lasers is dominated by non-thermal, intra-pulse plasma dynamics. The presence of multiple ion species or multiple charge states in targets leads to characteristic modulations and even mono-energetic features, depending on the choice of target material. As spectral signatures of generated ion beams are frequently used to characterize underlying acceleration mechanisms, thermal, multi-fluid descriptions require a revision for predictive capabilities and control in next-generation particle beam sources. We present an analytical model with explicit inter-species interactions, supported by extensive ab initio simulations. This enables us to derive important ensemble properties from the spectral distribution resulting from those multi-species effects for arbitrary mixtures. We further propose a potential experimental implementation with a

16.03.2019
14:43 MedicalNewsToday.comMedical News Today: Laser probe detects deadly melanoma in seconds

A Ph.D. student has designed a cost-effective and easy-to-use device that can quickly detect cancerous skin cells. Catching cancer earlier can save lives.

15.03.2019
17:20 Zdnet.comMy first laser cutter project: Saint Patrick's Day coasters

In less than two hours, David Gewirtz designed and produced a set of four wooden Saint Patrick's Day coasters using the Dremel Laser Cutter. Here's how.

08:50 Arxiv.org PhysicsLaser Driven Ultra-compact Undulator for Synchrotron Radiation. (arXiv:1903.06112v1 [physics.acc-ph])

Laser wakefield accelerators have emerged as a promising candidate for compact synchrotron radiation and even x-ray free electron lasers. Today, to make the electrons emit electromagnetic radiation, the trajectories of laser wakefield accelerated electrons are deflected by transverse wakefield, counter-propagating laser field or external permanent magnet insertion device. Here, we propose a novel type of undulator which has a few hundred microns of period and tens of Tesla of magnetic field. The undulator consists of a bifilar capacitor-coil target which sustains strong discharge current that generates helical magnetic field around the coil axis when irradiated by a high energy laser. Coupling this undulator with state-of-the-art laser wakefield accelerators can, simultaneously, produce ultra-bright quasi-monochromatic x-rays with tunable energy ranging 5-250 keV and optimize the free

08:16 Arxiv.org CSDetection and Tracking of Small Objects in Sparse 3D Laser Range Data. (arXiv:1903.05889v1 [cs.RO])

Detection and tracking of dynamic objects is a key feature for autonomous behavior in a continuously changing environment. With the increasing popularity and capability of micro aerial vehicles (MAVs) efficient algorithms have to be utilized to enable multi object tracking on limited hardware and data provided by lightweight sensors. We present a novel segmentation approach based on a combination of median filters and an efficient pipeline for detection and tracking of small objects within sparse point clouds generated by a Velodyne VLP-16 sensor. We achieve real-time performance on a single core of our MAV hardware by exploiting the inherent structure of the data. Our approach is evaluated on simulated and real scans of in- and outdoor environments, obtaining results comparable to the state of the art. Additionally, we provide an application for filtering the dynamic and mapping the static

14.03.2019
18:09 Phys.orgDuplicate or mirror? Laser light determines chirality of molecules

"In pharmaceutics, being able to transition a molecule from one chirality to the other using light instead of wet chemistry would be a dream," says Professor Reinhard Dörner from the Institute of Atomic Physics at Goethe University. His doctoral student Kilian Fehre has now brought this dream one step closer to coming true. His observation: the formation of the right- or left-handed version depends on the direction from which laser light hits the initiator.

04:28 Arxiv.org PhysicsFemtosecond laser-induced electron emission from nanodiamond-coated tungsten needle tips. (arXiv:1903.05560v1 [physics.app-ph])

We present femtosecond laser-induced electron emission from nanodiamond-coated tungsten tips. Based on the shortness of the femtosecond laser pulses, electrons can be photo-excited for wavelengths from the infrared (1932 nm) to the ultraviolet (235 nm) because multi-photon excitation becomes efficient over the entire spectral range. Depending on the laser wavelength, we find different dominant emission channels identified by the number of photons needed to emit electrons. Based on the band alignment between tungsten and nanodiamond, the relevant emission channels can be identified as specific transitions in diamond and its graphitic boundaries. It is the combination of the character of initial and final states (i.e. bulk or surface-near, direct or indirect excitation in the diamond band structure), the number of photons providing the excitation energy and the peak intensity of the laser

13.03.2019
07:03 Arxiv.org PhysicsShaping of laser-accelerated proton beam for radiobiology applications via genetic algorithm. (arXiv:1903.04787v1 [physics.med-ph])

Laser-accelerated protons have a great potential for innovative experiments in radiation biology due to the ultra short pulse duration and high dose rate achievable. However, the broad angular divergence makes them not optimal for applications with stringent requirements on dose homogeneity and total flux at the irradiated target. The solutions often adopted to increase the homogeneity are to spread the beam with a flat filter or to increase the distance between the source and the irradiation plane. Such methods considerably reduce the proton flux, which limits the performance of laser-accelerated protons for such applications. In this paper we demonstrate the use of a Genetic Algorithm (GA) to design an optimal non-flat filter to shape the beam and find a better trade-off between these two parameters. The filter takes advantage of the presence of chromatic focusing elements to further mix

12.03.2019
09:55 Arxiv.org PhysicsSurface plasmon polaritons on rough metal surfaces: Understanding the formation of laser induced periodic surface structures in metals. (arXiv:1903.04217v1 [physics.optics])

The formation of self-organized laser induced periodic surface structures (LIPSS) in metals, semiconductors and dielectrics upon pulsed laser irradiation is a well-known phenomenon, receiving increased attention due to its huge technological potential. For the case of metals, a major role in this process is played by surface plasmon polaritons (SPPs) propagating at the interface of the metal with the medium of incidence. Yet, simple and advanced models based on SPP propagation sometimes fail to explain experimental results, even of basic features as the LIPSS period. We experimentally demonstrate, for the particular case of LIPSS on Cu, that significant deviations of the structure period from the predictions of the standard model are observed, which are very pronounced for elevated angles of laser incidence. In order to explain this deviation, we introduce a model based on the propagation of

09:55 Arxiv.org PhysicsExtending the constraint for axion-like particles as resonances at the LHC and laser beam experiments. (arXiv:1903.04151v1 [hep-ph])

We study the discovery potential of axion-like particles (ALP), pseudo-scalars weakly coupled to Standard Model fields, at the Large Hadron Collider (LHC). Our focus is on ALPs coupled to the electromagnetic field, which would induce anomalous scattering of light-by-light. This can be directly probed in central exclusive production of photon pairs in ultra-peripheral collisions at the LHC in proton and heavy ion collisions. We consider non-standard collision modes of the LHC, such as argon-argon collisions at $\sqrt{s_{NN}} = 7$ TeV and proton-lead collisions at $\sqrt{s_{NN}} = 8.16$ TeV to access regions in the parameter space complementary to the ones previously considered for lead-lead or proton-proton collisions. In addition, we show that, using laser beam interactions, we can constrain ALPs as resonant deviations in the refractive index, induced by anomalous light-by-light scattering

09:55 Arxiv.org PhysicsSimulated Refraction-Enhanced X-Ray Radiography of Laser-Driven Shocks. (arXiv:1903.04020v1 [physics.plasm-ph])

Refraction-enhanced x-ray radiography (REXR) is used to infer shock-wave positions of more than one shock wave, launched by a multiple-picket pulse in a planar plastic foil. This includes locating shock waves before the shocks merge, during the early time and the main drive of the laser pulse that is not possible with the velocity interferometer system for any reflector. Simulations presented in this paper of REXR show that it is necessary to incorporate refraction and attenuation of x rays along with the appropriate opacity and refractive-index tables to interpret experimental images. Simulated REXR shows good agreement with an experiment done on the OMEGA laser facility to image a shock wave. REXR can be applied to design multiple-picket pulses with a better understanding of the shock locations. This will be beneficial to obtain the required adiabats for inertial confinement fusion

09:55 Arxiv.org PhysicsTwo-dimensional phase-space picture of the photonic crystal Fano laser. (arXiv:1903.03857v1 [physics.optics])

The recently realized photonic crystal Fano laser constitutes the first demonstration of passive pulse generation in nanolasers [Nat. Photonics $\boldsymbol{11}$, 81-84 (2017)]. We show that the laser operation is confined to only two degrees-of-freedom after the initial transition stage. We prove that the original 5D dynamic model can be reduced to a 1D model in a narrow region of the parameter space and it evolves into a 2D model after the exceptional point, where the eigenvalues transition from being purely to a complex conjugate pair. The 2D reduced model allows us to establish an effective band structure for the eigenvalue problem of the stability matrix to explain the laser dynamics. The reduced model is used to associate a previously unknown origin of instability with a new unstable periodic orbit separating the stable steady-state from the stable periodic orbit.

11.03.2019
05:30 Arxiv.org PhysicsSpatio-temporal structure of a Petawatt femtosecond laser beam. (arXiv:1903.03534v1 [physics.optics])

The development of optical metrology suited to ultrafast lasers has played a key role in the progress of these light sources in the last few decades. Measurement techniques providing the complete $E$-field of ultrashort laser beams in both time and space are now being developed. Yet, they had so far not been applied to the most powerful ultrashort lasers, which reach the PetaWatt range by pushing the Chirped Pulse Amplification scheme to its present technical limits. This situation left doubts on their actual performance, and in particular on the peak intensity they can reach at focus. In this article we present the first complete spatio-temporal characterization of a PetaWatt femtosecond laser operating at full intensity, the BELLA laser, using two recently-developed independent measurement techniques. Our results demonstrate that, with adequate optimization, the CPA technique is still

05:30 Arxiv.org PhysicsUnderstanding tunneling ionization of atoms in laser fields with the essence of multiphoton absorption. (arXiv:1903.03256v1 [physics.atom-ph])

The elaborate energy and momentum spectra of ionized electrons from atoms in laser fields suggest that the ionization dynamics described by tunneling theory should be modified. Although many efforts have been done within semiclassical models, there are few discussions describing multiphoton absorption process with quantum framework. In this letter, by comparing the results obtained with the time-dependent Schrodinger equation (TDSE) and Keldysh-Faisal-Reiss (KFR) theory, we have studied the nonperturbative effects of ionization dynamics beyond KFR theory. The difference in momentum spectra between multiphoton and tunneling regimes is understood in a unified picture with virtual multiphoton absorption processes. For the multiphoton regime, the momentum spectra can be obtained by coherent interference of each periodic contribution. However, the interference of multiphoton absorption peaks will

08.03.2019
11:22 Phys.orgWorld's first graffiti-busting laser helps Florence's 'Angels'

A beam of silver light erases scrawled black letters on Florence's historic Ponte Vecchio, as "Angels" wielding a revolutionary new laser wage war on graffiti in the UNESCO site.

06:31 Arxiv.org PhysicsRandom scattering and alternating projection optimization for active phase control of a laser beam array. (arXiv:1903.02780v1 [physics.optics])

A fraction of a laser beam array, whose unknown phase relationships must be set to prescribed values, is launched into a scattering media with random transmission. The resulting output speckle pattern is sampled by an array of photodiodes measuring the local light intensity. The data feed an innovative optimization process which control a phase modulator array. Few iterations of the opto-numeric loop lead to efficient and fast phase locking on any desired wavefront.

02:44 Nanowerk.comUsing laser 'tweezers', scientists grab and study tiny protein droplets

New research illuminates some basic properties of these eccentric marvels of biology.

07.03.2019
22:44 ScienceDaily.comUsing laser 'tweezers,' scientists grab and study tiny protein droplets

Physicists are using innovative tools to study the properties of a bizarre class of molecules that may play a role in disease: proteins that cluster together to form spherical droplets inside human cells. A new study sheds light on the conditions that drive such droplets to switch from a fluid, liquidy state to a harder, gel-like state.

20:03 Phys.orgUsing laser 'tweezers,' scientists grab and study tiny protein droplets

University at Buffalo physicists are using innovative tools to study the properties of a bizarre class of molecules that may play a role in disease: proteins that cluster together to form spherical droplets inside human cells.

09:07 Arxiv.org PhysicsCoercivity enhancement of selective laser sintered NdFeB magnets by grain boundary infiltration. (arXiv:1903.02233v1 [physics.app-ph])

Laser powder bed fusion is a well-established additive manufacturing method that can be used for the production of net-shaped Nd-Fe-B sintered magnets. However, low coercivity has been one of the drawbacks in the laser powder bed fusion processed Nd-Fe-B magnets. In this work, we have demonstrated that the grain boundary diffusion process using low-melting Nd-Cu, Nd-Al-Ni-Cu, and Nd-Tb-Cu alloys to the selective laser sintered NdFeB magnets can results in a substantial enhancement of coercivity from 0.65 T to 1.5 T. Detailed microstructure investigations clarified formation of Nd-rich grain boundary phase, introducing Tb-rich shell at the surface of Nd2Fe14B grains, and maintaining the grain size in nano-scale are responsible for the large coercivity enhancement.

02:37 Technology.orgScientists created a compact laser probe, which could help identifying melanoma early

Melanoma is the deadliest forms of skin cancer, but people can significantly improve their chances of survival by

06.03.2019
15:05 News-Medical.NetLaser-based technique allows doctors to image the whole eye in 3D

Scientists have developed a laser-based technique that can produce a full 3D image of all the layers of the retina, allowing doctors to better diagnose and treat eye diseases such as cataracts, diabetic retinopathy, and cancer.

13:58 Phys.orgVast record of past climate fluctuations now available thanks to laser imaging of shells

Shellfish played a significant role in the diet of prehistoric coastal populations, providing valuable nutrients. They are a common find in archaeological sites all over the world, usually in huge numbers, and researchers have long explored how they could be used to make inferences about the environments that humans experienced at those locations in the past. However, although techniques were developed to infer valuable climate-related information from shells, it was previously too expensive to analyse them on a scale beyond individual and isolated records. The current study by an international team of researchers, led by the Institute of Electronic Structure and Laser (Heraklion, Greece) and the School of Geography (Melbourne, Australia) and published in Scientific Reports, presents a technique to use rapid laser imaging to increase the number of analysed shell records to previously unknown

12:16 Technology.orgNew shapes of laser beam ‘sneak’ through opaque media

Researchers have found a way to pre-treat a laser beam so that it enters opaque surfaces without dispersing

11:52 Arxiv.org PhysicsEfficient all-optical helicity-dependent switching in Pt/Co/Pt with dual laser pulses. (arXiv:1903.01941v1 [cond-mat.mtrl-sci])

All-optical helicity-dependent switching (AO-HDS), deterministic control of magnetization by circularly polarized light pulses, allows to efficiently manipulate magnetization without the need of a magnetic field. While ferrimagnetic metals show single-shot magnetization switching, ferromagnetic metals require a large number of pulses to fully reverse the magnetic state from up to down or vice versa. Here, we demonstrate a drastic reduction in the number of pulses for full switching in a single stack of Pt/Co/Pt. To achieve this, we used pairs of optical pulses, a femtosecond linearly polarized pulse followed by a picosecond circularly polarized pulse. The obtained results suggest that the dual-pulse method is a potential route towards realizing efficient AO-HDS in ferromagnetic metals.

11:52 Arxiv.org PhysicsDetection of excited state absorption cross-section of porphyrin through cw and femto-second laser pump-probe technique. (arXiv:1903.01740v1 [physics.optics])

We report on direct detection of excited states absorption cross-section using dual wavelength pump-probe technique. Also, we experimentally demonstrate using porphyrin composite molecules (porphyrin derivatives such as 5,10,15,20-meso-tetrakis phenyl porphyrin (H2TPP), 5,10,15,20 - meso-tetrakis(4-hydroxyphenyl) porphyrin (H2TPP(OH)4)). The cw laser at 761 nm wavelength is used as a pump to maintain excited state population. Changes in the population of excited states lead to the change in transmission are monitored using femto-second probe pulses of 130 fs width and repeated at a 1kHz rate with central wavelength around 800 nm. Transmittance changes due to excited state population are modeled using rate equation approach. The effect of the absorption on the transmitted pulse shape has been discussed as a function of fluence. Obtained excited state absorption cross-sections of H2TPP and

11:52 Arxiv.org PhysicsSuperintense Laser-driven Ion Beam Analysis. (arXiv:1903.01725v1 [physics.plasm-ph])

Ion beam analysis techniques are among the most powerful tools for advanced material characterization. Despite their growing relevance in a widening number of fields, most ion beam analysis facilities still rely on the oldest accelerator technologies, with severe limitations in terms of portability and flexibility. In this work we thoroughly address the potential of superintense laser-driven proton sources for this application. We develop a complete analytical and numerical framework suitable to describe laser-driven ion beam analysis, exemplifying the approach for Proton Induced X-ray/Gamma-ray emission, a technique of widespread interest. This allows us to propose a realistic design for a compact, versatile ion beam analysis facility based on this novel concept. These results can pave the way for ground-breaking developments in the field of hadron-based advanced material

11:52 Arxiv.org PhysicsTopological properties of Weyl semimetals in circularly-polarized ultrafast laser field. (arXiv:1903.01657v1 [physics.optics])

We study the topological properties of three-dimensional Weyl semimetals in an ultrafast laser pulse. A single oscillation of circularly-polarized pulse induces the finite conduction band population in the reciprocal space which is highly structured and is determined by the topological phase. These textures can be probed by a linear polarized pulse which is applied after the circularly-polarized pulse. The response of the system to the linear probe pulse is highly dependent on the chirality of the circularly-polarized pulse. Also, we show that the induction conduction band population by a circularly-polarized pulse consisting of two oscillations with opposite chirality in the reciprocal space is highly chiral which represent the intrinsic chirality of the Weyl nodes.

05.03.2019
16:00 Phys.orgThe random anti-laser

The laser is the perfect light source—as long as it is provided with energy, it generates light of a specific, well-defined colour. However, it is also possible to create its opposite—an object that perfectly absorbs light of a particular colour and dissipates the energy almost completely.

07:18 Arxiv.org PhysicsEffect of laser frequency fluctuation on the decoherence rate of Rydberg polaritons. (arXiv:1902.09845v2 [physics.atom-ph] UPDATED)

The effect of electromagnetically induced transparency (EIT) using Rydberg-state atoms provides high optical nonlinearity to effectively mediate the photon-photon interaction. However, the decoherence rate of Rydberg polaritons, which plays an important role in the efficiency of optical nonlinear, can be largely influenced by the laser frequency fluctuation. In this work, we carry out a systematic theoretical and experimental study of effects of the laser frequency fluctuation on the EIT. We analyze a theoretical model that quantitatively describes the relationship between the decoherence rate and laser frequency fluctuation. The derived theoretical formula was experimentally verified for the $\Lambda$-type EIT system of laser-cooled $^{87}$Rb atoms, in which one can completely eliminate or controllably introduce the laser frequency fluctuation. We further extended the formula to include the

07:18 Arxiv.org PhysicsSelf-consistent quantum-kinetic theory for interplay between pulsed-laser excitation and nonlinear carrier transport in a quantum-wire array. (arXiv:1903.01425v1 [physics.optics])

We propose a self-consistent many-body theory for coupling the ultrafast dipole-transition and carrier-plasma dynamics in a linear array of quantum wires with the scattering and absorption of ultrashort laser pulses. The quantum-wire non-thermal carrier occupations are further driven by an applied DC electric field along the wires in the presence of resistive forces from intrinsic phonon and Coulomb scattering of photo-excited carriers. The same strong DC field greatly modifies the non-equilibrium properties of the induced electron-hole plasma coupled to the propagating light pulse, while the induced longitudinal polarization fields of each wire significantly alters the nonlocal optical response from neighboring wires. Here, we clarify several fundamental physics issues in this laser-coupled quantum wire system, including laser influence on local transient photo-currents, photoluminescence

07:18 Arxiv.org PhysicsBeam Distortion Effects upon focusing an ultrashort Petawatt Laser Pulse to greater than 10$^{22}$ W/cm$^{2}$. (arXiv:1903.00573v1 [physics.optics])

When an ultrashort laser pulse is tightly focused to a size approaching its central wavelength, the properties of the focused spot diverge from the diffraction limited case. Here we report on this change in behavior of a tightly focused Petawatt class laser beam by an F/1 off-axis paraboloid (OAP). Considering the effects of residual aberration, the spatial profile of the near field and pointing error, we estimate the deviation in peak intensities of the focused spot from the ideal case. We verify that the estimated peak intensity values are within an acceptable error range of the measured values. With the added uncertainties in target alignment, we extend the estimation to infer on-target peak intensities of $\geq$ 10$^{22}$ W/cm$^{2}$ for a target at the focal plane of this F/1 OAP.

03:30 Nanowerk.comNew shapes of laser beam 'sneak' through opaque media

Researchers have found a way to pre-treat a laser beam so that it enters opaque surfaces without dispersing - like a headlight that?s able to cut through heavy fog at full strength.

04.03.2019
23:02 ScienceDaily.comConcept of the laser can be reversed

Scientists have found a way to build the 'opposite' of a laser -- a device that absorbs a specific light wave perfectly. This can be done even in complicated systems, in which waves are scattered randomly, and has many technological applications.

19:03 Phys.orgNew shapes of laser beam 'sneak' through opaque media

Researchers have found a way to pre-treat a laser beam so that it enters opaque surfaces without dispersing—like a headlight that's able to cut through heavy fog at full strength.

10:00 Arxiv.org PhysicsThermal decoherence and laser cooling of Kerr microresonator solitons. (arXiv:1903.00431v1 [physics.optics])

Thermal noise is ubiquitous in microscopic systems and in high-precision measurements. Controlling thermal noise, especially using laser light to apply dissipation, substantially affects science in revealing the quantum regime of gases, in searching for fundamental physics, and in realizing practical applications. Recently, nonlinear light-matter interactions in microresonators have opened up new classes of microscopic devices. A key example is Kerr-microresonator frequency combs; so-called soliton microcombs not only explore nonlinear science but also enable integrated-photonics devices, such as optical synthesizers, optical clocks, and data-communications systems. Here, we explore how thermal noise leads to fundamental decoherence of soliton microcombs. We show that a particle-like soliton exists in a state of thermal equilibrium with its silicon-chip-based resonator. Therefore the soliton

10:00 Arxiv.org PhysicsPhotoelectric Effect at Sub-Photon Energy in Incident Pulsed Laser Radiation. (arXiv:1903.00285v1 [physics.optics])

Photoelectric effect in a Ge-on-Si single-photon avalanche detector (SPAD) at a sub-photon energy in incident pulsed laser radiation is considered in frames of classical electrodynamics of continuous media. It is shown that the energy of incident laser radiation, which is shared among a huge number of electrons in Ge matrix, can concentrate on only one of these through the effect of the constructive interference of the fields re-emitted by surrounding electrons. Conservation of energy in this case is upheld because of a substantial narrowing of the effective bandgap in heavily doped p-Ge, which is used in the design of considered SPAD.

10:00 Arxiv.org PhysicsPolarization shaping of high-order harmonics in laser-aligned molecules. (arXiv:1903.00039v1 [physics.atom-ph])

The present work reports on the generation of short-pulse coherent extreme ultraviolet radiation of controlled polarization. The proposed strategy is based on high-order harmonics generated in pre-aligned molecules. Field-free molecular alignment produced by a short linearly-polarized infrared laser pulse is used to break the isotropy of a gas medium. Driving the aligned molecules by a circularly-polarized infrared pulse allows to transfer the anisotropy of the medium to the polarization of the generated harmonic light. The ellipticity of the latter is controlled by adjusting the angular distribution of the molecules at the time they interact with the driving pulse. Extreme ultraviolet radiation produced with high degree of ellipticity (close to circular) is demonstrated.

01.03.2019
11:12 Arxiv.org PhysicsTemporal dependence of optically-induced photophoretic force on absorbing airborne particles by a power-modulated laser. (arXiv:1902.11177v1 [physics.optics])

Photophoretic force due to the optically-induced thermal effect provides an effective way to manipulate the light-absorbing particles suspended in ambient gases. However, how this force temporally responds to the intensity modulation of the illumination light is unclear. Here, by vertically trapping a micron-sized absorbing particle with a negative photophoretic force generated by a focused Gaussian beam, we demonstrate that the temporal change in the photophoretic force in response to the intensity modulation is remarkably slow (with a time constant up to ~1 s) due to the slow change in the particle's temperature. When the trapping beam is turned off for a few tens or hundreds of milliseconds, the trapped particle is found to be pulled up towards the light source by the remained photophoretic force, whereas when the intensity of the trapping beam is increased for a short duration, the

11:12 Arxiv.org PhysicsOptimizing Laser Pulses for Narrowband Inverse Compton Sources in the High-Intensity Regime. (arXiv:1902.10777v1 [physics.plasm-ph])

Scattering of ultraintense short laser pulses off relativistic electrons allows one to generate a large number of X- or $\gamma$-ray photons with the expense of the spectral width---temporal pulsing of the laser inevitable leads to considerable spectral broadening. In this Letter, we describe a simple method to generate optimized laser pulses that compensate the nonlinear spectrum broadening, and can be thought of as a superposition of two oppositely linearly chirped pulses delayed with respect to each other. We develop a simple analytical model that allow us to predict the optimal parameters of such a two-pulse---the delay, amount of chirp and relative phase---for generation of a narrowband {\gamma}-ray spectrum. Our predictions are confirmed by numerical optimization and simulations including 3D effects.

11:12 Arxiv.org PhysicsMeasurement of wave-particle interaction and metastable lifetime using laser-induced fluorescence. (arXiv:1902.10701v1 [physics.plasm-ph])

Extensive information, such as ion temperature and wave-particle interactions, can be obtained by direct measurement of ion distribution functions using laser-induced fluorescence (LIF). This nonintrusive plasma diagnostic provides an important window into the ion motions in phase-space. Previous simulation results suggest that LIF measurements, which are performed on metastable ions produced directly from neutral gas particles and also from ions in other electronic states, place restrictions on the metastable lifetime. In the case where metastable population is produced from direct ionization of neutral atoms, the velocity distribution measured using LIF will only faithfully represent processes which act on the ion dynamics in a time shorter than the metastable lifetime. In this paper, the metastable lifetime effects are explored experimentally for the first time using wave-particle

01:07 ScienceDaily.comFirst sypersymmetric laser array

A team of researchers has overcome a long-standing problem in laser science, and the findings could have applications in surgery, drilling and 3D laser mapping.

28.02.2019
20:49 Phys.orgResearchers develop first sypersymmetric laser array

A team of University of Central Florida researchers has overcome a long-standing problem in laser science, and the findings could have applications in surgery, drilling and 3-D laser mapping.

18:43 Technology.orgInstalling a Laser diode onto my home built CNC Router

I must first preface this story by stating that the LASER module, I first started with was a

06:52 Arxiv.org PhysicsDirect laser cooling to Bose-Einstein condensation in a dipole trap. (arXiv:1902.10361v1 [physics.atom-ph])

We present a method for producing three-dimensional Bose-Einstein condensates using \emph{only} laser cooling. The phase transition to condensation is crossed with $2.5 {\times} 10^{4}$ $^{87}$Rb atoms at a temperature of $T_c = 0.6$ $\mu$K after 1.4 s of cooling. Atoms are trapped in a crossed optical dipole trap, and cooled using Raman cooling with far-off-resonant optical pumping light to reduce atom loss and heating. The achieved temperatures are deep in the effective sub-recoil regime. We find that during the final cooling stage at atomic densities above $10^{14}$ cm$^{-3}$, careful tuning of trap depth and optical-pumping rate is necessary to evade heating and loss mechanisms. Our results pave the way for fast production of quantum degenerate gases in a variety of systems, including fermions and laser-cooled molecules.

06:31 Arxiv.org CSLearning to See the Wood for the Trees: Deep Laser Localization in Urban and Natural Environments on a CPU. (arXiv:1902.10194v1 [cs.RO])

Localization in challenging, natural environments such as forests or woodlands is an important capability for many applications from guiding a robot navigating along a forest trail to monitoring vegetation growth with handheld sensors. In this work we explore laser-based localization in both urban and natural environments, which is suitable for online applications. We propose a deep learning approach capable of learning meaningful descriptors directly from 3D point clouds by comparing triplets (anchor, positive and negative examples). The approach learns a feature space representation for a set of segmented point clouds that are matched between a current and previous observations. Our learning method is tailored towards loop closure detection resulting in a small model which can be deployed using only a CPU. The proposed learning method would allow the full pipeline to run on robots with

27.02.2019
18:06 Phys.orgHigh-tech laser scans uncover hidden military traverse at Alcatraz Island

High-tech radar and laser scans have uncovered a hidden military traverse underneath the infamous Alcatraz penitentiary, according to research led by faculty at Binghamton University, State University of New York.

09:49 Arxiv.org PhysicsLaser Cavity-Soliton Micro-Combs. (arXiv:1902.09930v1 [physics.optics])

The field of micro-cavity based frequency combs, or 'micro-combs'[1,2], has recently witnessed many fundamental breakthroughs[3-19] enabled by the discovery of temporal cavity-solitons, self-localised waves sustained by a background of radiation usually containing 95% of the total power[20]. Simple methods for their efficient generation and control are currently researched to finally establish micro-combs as out-of-the-lab widespread tools[21]. Here we demonstrate micro-comb laser cavity-solitons, an intrinsically highly-efficient, background free class of solitary waves. Laser cavity-solitons have underpinned key breakthroughs in semiconductor lasers[22,23] and photonic memories[24-26]. By merging their properties with the physics of both micro-resonators[1,2] and multi-mode systems[27], we provide a new paradigm for the generation and control of self-localised pulses in micro-cavities. We

09:49 Arxiv.org PhysicsReconfigurable Photonic Circuit for Controlled Power Delivery to Laser-Driven Accelerators on a Chip. (arXiv:1902.09731v1 [physics.optics])

Dielectric laser acceleration (DLA) represents a promising approach to building miniature particle accelerators on a chip. However, similar to conventional RF accelerators, an automatic and reconfigurable control mechanism is needed to scale DLA technology towards high energy gains and practical applications. We present a system providing control of the laser coupling to DLA using integrated optics and introduce a novel component for power distribution using a reconfigurable mesh of Mach-Zehnder interferometers. We show how such a mesh may be sequentially and efficiently tuned to optimize power distribution in the circuit and find that this strategy has favorable scaling properties with respect to size of the mesh.

08:56 Technology.orgNew multibeam metal 3D printer testbed to understand laser-material interactions

Lawrence Livermore National Laboratory (LLNL) scientists and engineers have created the first research-grade, open-architecture multibeam metal 3D printer

26.02.2019
12:44 Arxiv.org PhysicsAttosecond electro-optic effect in zinc sulfide induced by a laser field. (arXiv:1902.09351v1 [physics.optics])

An ultrafast anisotropic electro-optic effect of the zinc sulfide crystal is predicted employing a numerical pump-probe simulation. The numerical results indicate that the time-dependence of the anisotropic response of ZnS exhibits a phase shift with respect to the pump laser field. The phase shift coincides with the time-resolved dynamical Franz-Keldysh effect, which is the modulation of the isotropic part of the dielectric function. While the probe frequency dependence around the band gap is not intense, it becomes intense at higher photon energies of approximately 42~eV.

12:44 Arxiv.org PhysicsPropagation of ultra-short, resonant, ionizing laser pulses in rubidium vapor. (arXiv:1902.09281v1 [physics.optics])

We investigate the propagation of ultra-short laser pulses in atomic rubidium vapor. The pulses are intensive enough to ionize the atoms and are directly resonant with the 780 nm $D_2$ line. We derive a relatively simple theory for computing the nonlinear optical response of atoms and investigate the competing effects of strong resonant nonlinearity and ionization in the medium using computer simulations. A nonlinear self-channeling of pulse energy is found to produce a continuous plasma channel with complete ionization. We evaluate the length, width and homogeneity of the resulting plasma channel for various values of pulse energy and initial focusing to identify regimes optimal for applications in plasma-wave accelerator devices such as that being built by the AWAKE collaboration at CERN. Similarities and differences with laser pulse filamentation in atmospheric gases are

12:44 Arxiv.org PhysicsMagnetization reversal more rapidly by using an ultrashort square-wave laser pulse. (arXiv:1902.09057v1 [cond-mat.mes-hall])

With the feature of low-power magnetization manipulation at an ultrashort time scale, all optical switching (AOS) has been propelled to the forefront in investigations. To further speed up the magnetization reversal by manipulating ultrashort optical pulses, in this paper, one single square-wave laser pulse (SWLP) vie the combination of heating and Inverse Faraday Effect (IFE) is explored to excite the reversal of magnetization in a Co/Pt system. Simulation results show that the switching time of magnetization is 3 times faster than the using of a traditional Gaussian wave laser pulse (GWLP) under the same laser energy and pulse duration, and the threshold of AOS for the ferromagnet is 0.67 mJ/cm2. We furthermore demonstrate that the "heat accumulating effect" of laser-pulse is an important factor that influences the switching time, and a SWLP has a larger effect of heat accumulating than a

12:44 Arxiv.org PhysicsPrecision laser-based measurements of the single electron response of SPCs for the NEWS-G light dark matter search experiment. (arXiv:1902.08960v1 [physics.ins-det])

Spherical Proportional Counters (SPCs) are a novel gaseous detector technology employed by the NEWS-G low-mass dark matter search experiment for their high sensitivity to single electrons from ionization. In this paper, we report on the first characterization of the single electron response of SPCs with unprecedented precision, using a UV-laser calibration system. The experimental approach and analysis methodology are presented along with various direct applications for the upcoming next phase of the experiment at SNOLAB. These include the continuous monitoring of the detector response and electron drift properties during dark matter search runs, as well as the experimental measurement of the trigger threshold efficiency. We measure a mean ionization energy of $\mathrm{W}=27.6\pm0.2~\mathrm{eV}$ in $\mathrm{Ne + CH_4}$ $(2\%)$ for 2.8 keV X-rays, and demonstrate the feasibility of performing

12:44 Arxiv.org PhysicsCoherent Laser Induced Synthesis of Rare Earth Doped Nanocrystallites of 50PbO-25Bi$_2$O$_3$-20Ga$_2$O$_3$-5BaO. (arXiv:1902.08836v1 [cond-mat.mtrl-sci])

A principal possibility of formation the nanostructures on the surfaces of 50PbO-25Bi$_2$O$_3$-20Ga$_2$O$_3$-5BaO (doped by Eu3+, Er3+, Dy3+) is demonstrated by using multi-coherent beams. As a sources of the photoinducing coherent light we have used nanosecond Nd:YAG and Er:Yb lasers generating at 1064 nm and 1540 nm, respectively. The morphology of the photoinduced surfaces is sensitive to the type of rare earth ions. The thickness of the layer was about 20-30 nm. Possible mechanisms are explained by coherent photoinduction of the valence electrons.

12:21 Arxiv.org CSTransferability of Deep Learning Algorithms for Malignancy Detection in Confocal Laser Endomicroscopy Images from Different Anatomical Locations of the Upper Gastrointestinal Tract. (arXiv:1902.08985v1 [cs.CV])

Squamous Cell Carcinoma (SCC) is the most common cancer type of the epithelium and is often detected at a late stage. Besides invasive diagnosis of SCC by means of biopsy and histo-pathologic assessment, Confocal Laser Endomicroscopy (CLE) has emerged as noninvasive method that was successfully used to diagnose SCC in vivo. For interpretation of CLE images, however, extensive training is required, which limits its applicability and use in clinical practice of the method. To aid diagnosis of SCC in a broader scope, automatic detection methods have been proposed. This work compares two methods with regard to their applicability in a transfer learning sense, i.e. training on one tissue type (from one clinical team) and applying the learnt classification system to another entity (different anatomy, different clinical team). Besides a previously proposed, patch-based method based on

25.02.2019
22:44 ScienceDaily.comLaser drill leads to world record in plasma acceleration

Scientists have set a new world record for plasma accelerators: In a plasma tube only 20 centimeters long, the team has accelerated electrons to an energy of 7.8 billion electron volts (GeV).

19:02 Phys.orgLaser 'drill' sets a new world record in laser-driven electron acceleration

Combining a first laser pulse to heat up and "drill" through a plasma, and another to accelerate electrons to incredibly high energies in just tens of centimeters, scientists have nearly doubled the previous record for laser-driven particle acceleration.

24.02.2019
22:58 Technology.orgDiscovery, Unpacking, Setting up, Overview and Software Tests of the Endurance Laser

I’ve been looking at cheaper Chinese lasers online but i wasn’t sure about pulling the trigger and buying

22.02.2019
21:04 Gizmag Single-laser tech prints color graphics on metal

Although it's already possible to create colored images on metal surfaces using lasers, different types of lasers have to be used for different effects. Now, however, Russian scientists have developed a method of producing multiple effects using one commercially-available laser.
.. Continue Reading Single-laser tech prints color graphics on metal Category: Science Tags: Colors ITMO University Laser Metals

17:43 Phys.orgLaser-driven particle accelerator that can generate pairs of electron beams with different energies

Researchers at LMU have built the first-ever laser-driven particle accelerator that can generate pairs of electron beams with different energies.

08:59 Arxiv.org PhysicsSub-Doppler laser cooling of $^{39}$K via the 4S$\to$5P transition. (arXiv:1811.02185v2 [physics.atom-ph] UPDATED)

We demonstrate sub-Doppler laser cooling of $^{39}$K using degenerate Raman sideband cooling via the 4S$_{1/2} \rightarrow$5P$_{1/2}$ transition at 404.8 nm. By using an optical lattice in combination with a magnetic field and optical pumping beams, we obtain a spin-polarized sample of up to $5.6 \times 10^{7}$ atoms cooled down to a sub-Doppler temperature of 4 $\mu$K, reaching a peak density of $3.9 \times 10^{9}$ atoms/cm$^{3}$, a phase-space density greater than $10^{-5}$, and an average vibrational level of $\langle \nu \rangle=0.6$ in the lattice. This work opens up the possibility of implementing a single-site imaging scheme in a far-detuned optical lattice utilizing shorter wavelength transitions in alkali atoms, thus allowing improved spatial resolution.

20.02.2019
20:39 Technology.orgThe diversified application of laser heads

Due to the recent advancement in technology, the designing industry is able to manufacture products with an extreme

10:32 Technology.orgA POLARITON FILTER TURNS ORDINARY LASER LIGHT INTO QUANTUM LIGHT

An international team of researchers led out of Macquarie University has demonstrated a new approach for converting ordinary

07:05 Arxiv.org Physics946-nm Nd:YAG digital-locked laser at $1.1\times10^{-16}$ in 1 s and transfer-locked to a cryogenic silicon cavity. (arXiv:1902.07012v1 [physics.optics])

We present a Nd:YAG ultra-stable laser system operating at 946 nm and demonstrate a fractional frequency instability of $1.1\times10^{-16}$ at 1 s by pre-stabilizing it to a 30 cm-long ULE cavity at room temperature. All key analog components have been replaced by FPGA-based digital electronics. To reach an instability below the $10^{-16}$ level, we transfer the stability of a 1542 nm laser stabilized to a cryogenic silicon cavity exhibiting a fractional frequency instability of $4\times10^{-17}$ at 1 s to the laser at 946 nm.

07:05 Arxiv.org PhysicsUncertainty Analysis of Microsegregation during Laser Powder Bed Fusion. (arXiv:1902.06785v1 [physics.app-ph])

Quality control in additive manufacturing can be achieved through variation control of the quantity of interest (QoI). We choose in this work the microstructural microsegregation to be our QoI. Microsegregation results from the spatial redistribution of a solute element across the solid-liquid interface that forms during solidification of an alloy melt pool during the laser powder bed fusion process. Since the process as well as the alloy parameters contribute to the statistical variation in microstructural features, uncertainty analysis of the QoI is essential. High-throughput phase-field simulations estimate the solid-liquid interfaces that grow for the melt pool solidification conditions that were estimated from finite element simulations. Microsegregation was determined from the simulated interfaces for different process and alloy parameters. Correlation, regression, and surrogate model

19.02.2019
23:32 Phys.orgSingle-laser techniques make reproducible artwork on metal without dye or paint

A variety of laser-based techniques can be used to produce colorful artwork on metals. However, each approach typically requires a different type of laser and very specific settings. In a new study, researchers describe how to use a single commercially available laser to achieve three techniques for laser colorization on metal, making the techniques more practical for a wide range of applications in art and jewelry making, with the possibility of mass production.

22:20 ScienceDaily.comNew laser methods create dazzling colors on metals

Researchers describe how to use a single commercially available laser to achieve three techniques for laser colorization on metal, making the techniques more practical for a wide range of applications in art and jewelry making.

15:35 Phys.orgA polariton filter turns ordinary laser light into quantum light

An international team of researchers led out of Macquarie University has demonstrated a new approach for converting ordinary laser light into genuine quantum light.

09:35 Arxiv.org PhysicsSingle-step fabrication of surface waveguides in fused silica with few-cycle laser pulses. (arXiv:1902.06727v1 [physics.app-ph])

Direct laser writing of surface waveguides with ultrashort pulses is a crucial achievement towards all-laser manufacturing of photonic integrated circuits sensitive to their environment. In this Letter, few-cycle laser pulses (with a sub-10 fs duration) are used to produce subsurface waveguides in a non-doped, non-coated fused silica substrate. The fabrication technique relies on laser-induced microdensification below the threshold for nanopore formation. The optical losses of the fabricated waveguides are governed by the optical properties of the superstrate. We have measured losses ranging from less than 0.1~dB/mm (air superstrate) up to 2.8~dB/mm when immersion oil is applied on top of the waveguide.

09:35 Arxiv.org PhysicsPulsing mechanism based on power adiabatic evolution of pump in Tm-doped fiber laser. (arXiv:1902.06618v1 [physics.optics])

We prove an alternative pulsing mechanism based on power adiabatic evolution of pump in Tm-doped fiber laser. A pulsed laser technique, unlike Q-switching and gain-switching, is explored under the equilibrium between the stimulated emission and absorption. After the laser reaching a CW steady state, the temporal fluctuation of pump power is called power adiabatic evolution if it does not break the balance between the stimulated emission and the absorption. Under the pump power adiabatic evolution the population densities in the upper and lower laser levels get clamped to their threshold values as before, and the temporal shape of output laser are identical with that of pump. Based on the power adiabatic evolution of pump a laser pulse can therefore be generated. Moreover, the temporal profile, duration and peak power of the laser pulse can all be precisely controlled. Some requirements on the

09:35 Arxiv.org PhysicsIntegrated frequency comb laser with narrow intrinsic optical linewidth based on a dielectric waveguide feedback circuit. (arXiv:1902.06544v1 [physics.optics])

We present an integrated hybrid semiconductor-dielectric (InP-Si$_3$N$_4$) waveguide laser that generates frequency combs at a wavelength around 1.5 $\mu$m with a record-low intrinsic optical linewidth of 34 kHz. This is achieved by extending the cavity photon lifetime using a low-loss dielectric waveguide circuit. In our experimental demonstration, the on-chip, effective optical path length of the laser cavity is extended to 6 cm. The resulting linewidth narrowing shows the high potential of on-chip, highly coherent frequency combs with direct electrical pumping, based on hybrid and heterogeneous integrated circuits making use of low-loss dielectric waveguides.

18.02.2019
22:01 ScienceDaily.comResearchers discover anti-laser masquerading as perfect absorber

Researchers have discovered that a perfect absorber of electromagnetic waves they described in a 2017 paper can easily be tweaked into a sort of 'time-reversed laser' known as a coherent perfect absorber (CPA).

13:46 Technology.orgLaser-induced graphene gets tough, with help

Laser-induced graphene (LIG), a flaky foam of the atom-thick carbon, has many interesting properties on its own but gains new

05:13 Arxiv.org PhysicsCoherent optical modulation of partially mode-locked fiber laser based on coherent population oscillation in reduced oxide graphene. (arXiv:1902.05901v1 [physics.optics])

Optical control of graphene-based photonic devices and systems has been under extensive explorations, nevertheless, the requirement of high power pump laser due to incoherent modulation makes those schemes low efficient. Here, we demonstrate coherent manipulation of the operating states of partially mode-locked fiber laser based on coherent population oscillation in reduced graphene oxide for the first time. We couple a much weaker continuous wave laser into the resonator operating with parametric instability state, and observe significant depression/enhancement of the sidebands when the coherent population oscillation conditions are satisfied. Besides, significant depression of partially mode-locked fiber laser is achieved. The experimental results reveal that the coherent population oscillation in reduced graphene oxide is highly effective in manipulating mode-locked fiber laser system, and

05:13 Arxiv.org PhysicsLaser cooling of molecules. (arXiv:1902.05628v1 [physics.atom-ph])

Recently, laser cooling methods have been extended from atoms to molecules. The complex rotational and vibrational energy level structure of molecules makes laser cooling difficult, but these difficulties have been overcome and molecules have now been cooled to a few microkelvin and trapped for several seconds. This opens many possibilities for applications in quantum science and technology, controlled chemistry, and tests of fundamental physics. This article explains how molecules can be decelerated, cooled and trapped using laser light, reviews the progress made in recent years, and outlines some future applications.

16.02.2019
18:27 WhatReallyHappened.comSix dead in US warehouse massacre: Fired worker, 45, who used pistol with laser sight to kill five of his co-workers at company where he had worked for 20 years is killed by cops in stand-off that left five officers hurt (10 Pics)

15.02.2019
19:11 Phys.orgResearchers discover anti-laser masquerading as perfect absorber

Researchers at Duke University have discovered that a perfect absorber of electromagnetic waves they described in a 2017 paper can easily be tweaked into a sort of "time-reversed laser" known as a coherent perfect absorber (CPA).

17:30 Phys.orgLaser pulses light the way to tuning topological materials for spintronics and quantum computing

Scientists at the U.S. Department of Energy's Ames Laboratory have discovered a means of controlling the surface conductivity of a three-dimensional (3-D) topological insulator, a type of material that has potential applications in spintronic devices and quantum computing.

06:08 Arxiv.org PhysicsExtremely intense laser-based electron acceleration in a plasma channel. (arXiv:1902.05427v1 [physics.plasm-ph])

Laser pulses of extreme intensities ($I>10^{22}~ \mathrm{W/cm^2}$) are about to become available in the laboratory. The prepulse of such a laser can induce a plasma expansion that generates a low-density channel in near-critical gas jets. We present a study of channel formation and subsequent direct laser acceleration of electrons within the pre-formed channel. Radiation reaction affects the acceleration in several ways. It first interferes with the motion of the return current on the channel walls. In addition, it reduces the radial expelling efficiency of the transverse ponderomotive force, leading to the radiative trapping of particles near the channel axis. These particles then interact with the peak laser intensity and can attain multi-GeV energies.

06:08 Arxiv.org PhysicsAutoionization dynamics of He nanodroplets resonantly excited by intense XUV laser pulses. (arXiv:1902.05332v1 [physics.atm-clus])

The ionization dynamics of helium droplets in a wide size range from 220 to 10^6 He atoms irradiated with intense femtosecond extreme ultraviolet (XUV) pulses of 10^9 {\div} 10^{12} W/cm2 power density is investigated in detail by photoelectron spectroscopy. Helium droplets are resonantly excited in the photon energy range from ~ 21 eV (corresponding to the atomic 1s2s state) up to the atomic ionization potential (IP) at ~ 25 eV. A complex evolution of the electron spectra as a function of droplet size and XUV intensity is observed, ranging from atomic-like narrow peaks due to binary autoionization, to an unstructured feature characteristic of electron emission from a nanoplasma. The experimental results are analyzed and interpreted with the help of numerical simulations based on rate equations taking into account various processes such as multi-step ionization, interatomic Coulombic decay

06:08 Arxiv.org PhysicsLaser cooling with adiabatic passage for diatomic molecules. (arXiv:1902.05212v1 [physics.atom-ph])

We demonstrate a magnetically enhanced laser cooling scheme applicable to multi-level type-II transitions and further diatomic molecules with adiabatic transfer. An angled magnetic field is introduced to not only remix the dark states, but also decompose the multi-level system into several two-level sub-systems in time-ordering, hence allowing multiple photon scattering as long as the Zeeman shift is sufficiently large. For complex 4+12 level diatomic molecules, we observe a $\sim 4\times$ enhancement of the damping coefficient and a rather wide cooling velocity range compared to the conventional Doppler cooling. A reduced dependence on spontaneous emission of this scheme makes laser cooling systems with leakage channels become a feasibility.

14.02.2019
08:56 Arxiv.org PhysicsLaser wakefield driven generation of isolated CEP-tunable intense sub-cycle pulses. (arXiv:1902.05014v1 [physics.optics])

Sources of intense, ultra-short electromagnetic pulses are enabling applications such as attosecond pulse generation, control of electron motion in solids and the observation of reaction dynamics at the electronic level. For such applications both high-intensity and carrier envelope phase (CEP) tunability is beneficial, yet hard to obtain with current methods. In this work we present a new scheme for generation of isolated CEP-tunable intense sub-cycle pulses with significant spectral power from mid-IR to extreme UV. It utilizes an intense driver laser pulse which drives a wake in a plasma, co-propagating with a long-wavelength seed pulse. The moving electron density peaks of the wake amplify the seed and form sub-cycle pulses. Controlling the CEP of the seed pulse or the driver-seed delay leads to CEP-tunability, while frequency tunability can be achieved by adjusting the laser and plasma

08:56 Arxiv.org PhysicsHigh current sub-femtosecond electron bunches via magnetic field induced injection braking in laser wakefield acceleration. (arXiv:1902.04771v1 [physics.plasm-ph])

It is found that the three-dimensional laser-driven plasma bubble and the electron injection process can be manipulated by incorporating an external magnetic field and a plasma density gradient both along the longitudinal direction. The down-ramp of a density-profile-tailored plasma increases the wavelength of the plasma wake and hence reduces its phase velocity, which helps to trigger the electron injection. While a longitudinal magnetic field induces dynamically an expanding electron density hole in the rear of the wake bubble, which tends to reduce the peak electron velocity there. Electron injection is braked as soon as the electron peak velocity is less than the phase velocity when the density hole is large enough. Consequently, the start and end positions of electron injection can be flexibly controlled, which can lead to sub-femotsecond electron bunches with the peak current of a few

08:56 Arxiv.org PhysicsCorrelated emission of X-ray and sound from water film irradiated by femtosecond laser pulses. (arXiv:1902.04726v1 [physics.app-ph])

Simultaneous measurements of hard X-ray by a Geiger counter and audible sound (10 Hz-20kHz) by a microphone from a thin water film in air were carried out under intense single and double pulse irradiations of femtosecond laser (35 fs, 800 nm, 1 kHz). Emission profiles of X-ray and sound under the single pulse irradiation by changing the water film position along the laser incident direction (Z-axis) show the same peak positions with a broader emission in sound (403{\mu}m at FWHM) than in X-ray (37{\mu}m). Under the double pulse irradiation condition with the time delay at 0 ps and 4.6 ns, it was clearly observed that the acoustic signal intensity is enhanced in associated with X-ray intensity enhancements. The enhancements can be assigned to laser ablation dynamics such as pre-plasma formation and transient surface roughness formation induced by the pre-pulse irradiation. For the acoustic

08:56 Arxiv.org PhysicsHigh repetition rate (

High intensity laser-plasma interactions produce a wide array of energetic particles and beams with promising applications. Unfortunately, high repetition rate and high average power requirements for many applications are not satisfied by the lasers, optics, targets, and diagnostics currently employed. Here, we address the need for high repetition rate targets and optics through the use of liquids. A novel nozzle assembly is used to generate high-velocity, laminar-flowing liquid microjets which are compatible with a low-vacuum environment, generate little to no debris, and exhibit precise positional and dimensional tolerances. Jets, droplets, submicron thick sheets, and other configurations are characterized with pump-probe shadowgraphy to evaluate their use as targets. To demonstrate a high repetition rate, consumable liquid optical element, we present a plasma mirror created by a submicron

13.02.2019
23:29 Phys.orgResearch team develops a high-performance quantum dot mode-locked laser on silicon

Ten years into the future. That's about how far UC Santa Barbara electrical and computer engineering professor John Bowers and his research team are reaching with the recent development of their mode-locked quantum dot lasers on silicon. It's technology that not only can massively increase the data transmission capacity of data centers, telecommunications companies and network hardware products to come, but do so with high stability, low noise and the energy efficiency of silicon photonics.

23:02 ScienceDaily.comHigh-performance quantum dot mode-locked laser on silicon

Ten years into the future. That's about how far an electrical and computer engineering professor and his research team are reaching with the recent development of their mode-locked quantum dot lasers on silicon. It's technology that not only can massively increase the data transmission capacity of data centers, telecommunications companies and network hardware products to come, but do so with high stability, low noise and the energy efficiency of silicon photonics.

20:52 Nanowerk.comEngineers develop high-performance quantum dot mode-locked laser on silicon

This future technology not only can massively increase the data transmission capacity of data centers, telecommunications companies and network hardware products to come, but do so with high stability, low noise and the energy efficiency of silicon photonics.

15:09 Phys.orgMultimaterial 3-D laser microprinting using an integrated microfluidic system

Complex, three-dimensional (3-D) structures are regularly constructed using a reliable commercial method of 3-D laser micro- and nanoprinting. In a recent study, Frederik Mayer and co-workers in Germany and Australia have presented a new system in which a microfluidic chamber could be integrated on a laser 3-D lithography device to construct multimaterial structures using more than one constituent material. The new method can eliminate the existing need to transfer between lithography techniques and chemistry labs for a streamlined manufacturing process.

11:34 Arxiv.org PhysicsInvestigation of robust population transfer using quadratically chirped laser interacting with two-level system. (arXiv:1902.04267v1 [physics.atom-ph])

We have proposed and demonstrated a fast and robust method of population transfer between two quantum states using a quadratically chirped laser source. Incorporating the Jaynes-Cummings in a full quantum description of the interaction, and numerically solving the time-dependent Schr\"odinger equation, transition probabilities have been obtained and the condition of the adiabatic passage is investigated. In this scheme, a laser source has been swept quadratically in time for arbitrarily engineering the transition probabilities. The results show that complete and robust population transfer could be selectively achieved by appropriate adjusting of the laser chirping parameter, the center frequency and the coupling strength which the time of the complete transition could be drastically decreased compared to linearly traditional chirped laser. Furthermore, another feature of using the

11:34 Arxiv.org PhysicsImproving performance of inverse Compton sources through laser chirping. (arXiv:1902.04240v1 [physics.acc-ph])

We present a new paradigm for computation of radiation spectra in the non-linear regime of operation of inverse Compton sources characterized by high laser intensities. The resulting simulations show an unprecedented level of agreement with the experiments. Increasing the laser intensity changes the longitudinal velocity of the electrons during their collision, leading to considerable non-linear broadening in the scattered radiation spectra. The effects of such ponderomotive broadening are so deleterious that most inverse Compton sources either remain at low laser intensities or pay a steep price to operate at a small fraction of the physically possible peak spectral output. This ponderomotive broadening can be reduced by a suitable frequency modulation (also referred to as "chirping", which is not necessarily linear) of the incident laser pulse, thereby drastically increasing the peak

04:23 ScienceDaily.comLaser-induced graphene gets tough, with help

Laser-induced graphene combines with many materials to make tough, conductive composites for wearable electronics, anti-icing, antimicrobial applications, sensors and water treatment.

00:16 LiveScience.comGorgeous Fractal Patterns, Normally Found Only in Nature, Re-Created Using Laser Light

A human-made thing created a very beautiful, natural pattern.

00:16 Phys.orgLaser-induced graphene gets tough, with help

Laser-induced graphene (LIG), a flaky foam of the atom-thick carbon, has many interesting properties on its own but gains new powers as part of a composite.

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