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17.01.2019
03:52 BBCCan laser shoes help people with Parkinson's walk?

People with Parkinson's can freeze when they walk but laser shoes are helping them to keep moving.

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16.01.2019
06:29 Arxiv.org PhysicsImprint of the stochastic nature of photon emission by electrons on the proton energy spectra in the laser-plasma interaction. (arXiv:1901.04632v1 [physics.plasm-ph])

In QED the photon emission process is probabilistic in contrast to classical radiation theory that significantly modifies radiation reaction in ultrastrong laser fields. This fundamental property of photon emission - stochasticity effect (SEs) - can be probed in the electron-laser beam interaction via electron characteristics as shown previously theoretically, but challenging to observe experimentally. In this work we investigate theoretically SEs for the proton energy spectra during laser-plasma interaction in the quantum radiation-dominated regime, which may facilitate SEs experimental observation. An ultrarelativistic plasma generated and driven by an ultraintense laser pulse, collides head-on with counterpropagating laser pulse, which decelerates the electrons due to radiation reaction, and results in significant compression of the proton energy spectra because of the charge separation

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15.01.2019
17:39 Phys.orgThree-dimensional femtosecond laser nanolithography of crystals

Optical properties of materials are based on their chemistry and the inherent subwavelength architecture, although the latter remains to be characterized in depth. Photonic crystals and metamaterials have proven this by providing access through surface alterations to a new level of light manipulation beyond the known natural optical properties of materials. Yet, in the past three decades of research, technical methods have been unable to reliably nanostructure hard optical crystals beyond the material surface for in-depth optical characterization and related applications.

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17:39 Phys.orgBright colors produced by laser heating

Most of the colors on today's paper and fabric are made using dyes or pigments. But colors can also be produced by modifying a material's surface at the nanoscale, causing the surface to reflect or scatter different frequencies of light and giving these materials "structural color." Butterfly wings and bird feathers are examples of materials that naturally exhibit structural color.

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09:19 Arxiv.org PhysicsPhysics of the laser-plasma interface in the relativistic regime of interaction. (arXiv:1901.04175v1 [physics.plasm-ph])

The reflection of intense laser radiation from solids appears as a result of relativistic dynamics of the electrons driven by both incoming and self-generated electromagnetic fields at the periphery of the emerging dense plasma. In the case of highly-relativistic motion, electrons tend to form a thin oscillating layer, which makes it possible to model the interaction and obtain the temporal structure of the reflected radiation. The modelling reveals the possibility and conditions for producing singularly intense and short XUV bursts of radiation, which are interesting for many applications. However, the intensity and duration of the XUV bursts, as well as the high-energy end of the harmonic spectrum, depends on the thickness of the layer and its internal structure which are not assessed by such macroscopic modelling. Here we analyse the microscopic physics of this layer and clarify how its

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09:19 Arxiv.org PhysicsTerahertz radiation generated by shell electrons in the bubble regime via the interaction between an intense laser and underdense plasma. (arXiv:1901.04114v1 [physics.plasm-ph])

Backward terahertz radiation can be produced by a high-intensity laser normally incident upon an underdense plasma. It is found that terahertz radiation is generated by electrons refluxing along the bubble shell. These shell electrons have similar dynamic trajectories and emit backward radiations to vacuum. This scheme has been proved through electron dynamic calculations as well as by using an ionic sphere model. In addition, the bubble shape is found to influence the radiation frequency, and this scheme can be implemented in both uniform and up-ramp density gradient plasma targets. The terahertz radiation may be used for diagnosing the electron bubble shape in the interaction between an intense laser and plasma. All results are presented via 2.5 dimensional particle-in-cell simulations.

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09:03 3dnewsПроектор Xiaomi 4K Mijia Laser Projector TV оценён в $1500

Китайская компания Xiaomi анонсировала лазерный проектор 4K Mijia Laser Projector TV, приём заказов на который начнётся уже до конца текущей недели. Устройство позволяет формировать изображение размером от 80 до 150 дюймов по диагонали. Разрешение составляет 3840 × 2160 пикселей, что соответствует формату 4К. Говорится о поддержке HDR10.

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11.01.2019
06:00 Arxiv.org PhysicsAlignment of the CS$_2$ Dimer Embedded in Helium Droplets Induced by a Circularly Polarized Laser Pulse. (arXiv:1901.03184v1 [physics.chem-ph])

Dimers of carbon disulfide (CS$_2$) molecules embedded in helium nanodroplets are aligned using a moderately intense, 160ps, non-resonant, circularly polarized laser pulse. It is shown that the intermolecular carbon-carbon (C-C) axis aligns along the axis perpendicular to the polarization plane of the alignment laser pulse. The degree of alignment, quantified by $\langle \cos^2(\theta_\text{2D}) \rangle$, is determined from the emission directions of recoiling CS$_2$$^+$ fragment ions, created when an intense 40fs probe laser pulse doubly ionizes the dimers. Here, $\theta_\text{2D}$ is the projection of the angle between the C-C axis on the 2D ion detector and the normal to the polarization plane. $\langle \cos^2(\theta_\text{2D}) \rangle$ is measured as a function of the alignment laser intensity and the results agree well with $\langle \cos^2(\theta_\text{2D}) \rangle$ calculated for

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10.01.2019
19:04 Telegraph.co.ukCES 2019: Bosch develops tiny laser to put touchscreens in your wardrobe

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16:43 Phys.orgLaser triggers electrical activity in thunderstorm for the first time

A team of European scientists has deliberately triggered electrical activity in thunderclouds for the first time, according to a new paper in the latest issue of Optics Express, the Optical Society's (OSA) open-access journal. They did this by aiming high-power pulses of laser light into a thunderstorm.

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10:31 Gizmag Bosch's tiny laser projection module puts touchscreens in your wardrobe


It looks like nothing in your house is safe from becoming "smart." Case in point: At CES this week Bosch has unveiled a device that could be fitted to furniture to plug regular old shelves into the Internet of Things. The BML100PI module (which could use a zippier name) projects a touchscreen onto shelves to help you pick out an outfit or book a laundry pickup.
.. Continue Reading Bosch's tiny laser projection module puts touchscreens in your wardrobe Category: Around The Home Tags: Bosch CES 2019 Internet of Things Projector Projectors Touchscreen

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08:44 Arxiv.org PhysicsFemtosecond-Laser-Induced Spin-Polarized Electron Emission from a GaAs Tip. (arXiv:1901.02741v1 [physics.optics])

It is shown that focusing circularly-polarized 800 nm light pulses of 100 fs duration on the tips of p-GaAs crystalline shards having no negative electron affinity (NEA) activation results in electron emission that is both fast and spin-polarized. The 400 fs duration of the emission process was determined by pump/probe measurements. The three samples we investigated produced electron polarizations of 13.1(9)%, 13.3(7)%, and 10.4(2)%. Emission currents ranged between 50 pA and 3 nA with a sample bias of -100V and average laser power of 100 mW. The electron emission exhibited linear dichroism and was obtained under moderate vacuum conditions, similar to that of metallic tips. This source of spin-polarized electron pulses is "fast" in the sense that the electron emission process is of comparable duration to the laser pulses that initiate it.

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08:44 Arxiv.org PhysicsSubwavelength periodic plasma structures formed during the laser-pulse-induced breakdown within the transparent dielectric. (arXiv:1901.02649v1 [physics.plasm-ph])

The spatiotemporal evolution of the field and plasma in the optical breakdown induced in the volume of transparent dielectric (fused silica) by the focused fs laser pulse is studied under condition of the so-called plasma-resonance-induced ionization instability that results in the deep small-scale periodic modulation of the breakdown plasma parameters in the direction of the laser polarization. In the framework of the model used, the optical electric field was calculated with allowance for the effects influencing both its long-scale structure (the beam focusing accounted for in the given-ray-tube approximation, phase and group delays, and back reflection) and the small-scale one (quasi-static enhancement in the plasma resonance regions). The plasma density evolution is described by the rate equation taking into account the photoionization, avalanche ionization, and ambipolar diffusion. Based

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08:44 Arxiv.org PhysicsPenning collisions between supersonically expanded metastable helium atoms and laser-cooled lithium atoms. (arXiv:1901.02482v1 [physics.chem-ph])

We describe an experimental setup comprised of a discharge source for supersonic beams of metastable helium atoms and a magneto-optical trap (MOT) for ultracold lithium atoms that makes it possible to study Penning ionization and associative ionization processes at high ion count rates. The cationic reaction products are analyzed using a novel ion detection scheme which allows for mass selection, a high ion extraction efficiency and a good collision-energy resolution. The influence of elastic He-Li collisions on the steady-state Li atom number in the MOT is described, and the collision data are used to estimate the excitation efficiency of the discharge source. We also show that Penning collisions can be directly used to probe the temperature of the Li cloud without the need for an additional time-resolved absorption or fluorescence detection system.

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01:47 News-Medical.NetRussian scientists propose new method to study tissue changes after laser surgery

Although currently laser surgery is a very popular tool for various vision disorders correction, it is still difficult to ensure proper control over the accuracy, efficiency and safety of such procedures.

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09.01.2019
13:35 Nature.ComDreaming of death rays: the search for laser weapons

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08.01.2019
06:58 Arxiv.org PhysicsRobustness of topologically sensitive harmonic generation in laser-driven linear chains. (arXiv:1901.01437v1 [physics.atom-ph])

A huge difference in the harmonic yield from the two topological phases of finite, dimerizing linear chains in laser fields has recently been observed in all-electron time-dependent density functional simulations [D. Bauer, K.K. Hansen, Phys. Rev. Lett. 120, 177401 (2018)]. In this work, we explore the robustness of the effect concerning the size of the chains, a continuous transition between the two topological phases, and disorder. A high robustness of both the degeneracy of the edge states in the topologically non-trivial phase and of the pronounced destructive interference causing a dip in the harmonic spectra in the topologically trivial phase is observed.

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07.01.2019
09:34 Arxiv.org PhysicsFrequency-modulated continuous-wave laser distance measurement system using Fabry- Perot cavity as measuring reference. (arXiv:1901.01131v1 [physics.ins-det])

Frequency-modulated continuous-wave (FMCW) is a ranging technique that allows for high precision distance measurement over long distances. Scanning nonlinearity and range of the tunable laser are the main factors affecting the measurement accuracy. Frequency-sampling method is a recognized post-processing scheme to compensate the scanning nonlinearity. In this work, an FMCW laser distance measurement system using a high fineness Fabry-Perot (F-P) cavity as a sampling reference is demonstrated. The frequency of the resampled signal is calculated with a Hilbert transform. The high stability of the F-P cavity and the advantages of the Hilbert transform lead to a high measurement precision when an external cavity diode laser (ECDL) with a scanning range of tens of GHz is available. In this experiment, the scanning range of the ECDL is only 88 GHz, and a measurement uncertainty of 76.8 um (with

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09:34 Arxiv.org PhysicsInfrared Laser Locking to Rubidium Saturated Absorption Spectrum via a Photonic Chip Frequency Doubler. (arXiv:1901.00922v1 [physics.ins-det])

Photonic integrated resonators stand out as reliable frequency converters due to their compactness and stability, with second-harmonic generation (SHG) efficiencies of up to 17000%/W reported recently in aluminum nitride microrings. In this work, a sufficiently strong second-harmonic (SH) signal up to microwatts was generated by a photonic integrated frequency doubler using a milliwatt infrared (IR) laser source. Furthermore, increased SHG bandwidth covering $^{85}$Rb and $^{87}$Rb D$_2$ transition lines as well as saturated absorption spectroscopy (SAS) were demonstrated by tuning the pump power and chip temperature. Here, we present, to the best of our knowledge, the first successful locking of an IR laser to Rb saturated absorption lines via a photonic chip frequency doubler.

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06.01.2019
07:44 Gizmag Laser CubeSats could become artificial stars to keep space telescopes focused


NASA is poised to send larger and larger telescopes into space over the next couple of decades and a team of researchers at MIT is working out how to use CubeSats to keep them fixed on target. Using lasers, the bread-loaf sized spacecraft will serve as artificial guide stars to act as points of reference and make sure the giant scopes are tracking and focusing properly.
.. Continue Reading Laser CubeSats could become artificial stars to keep space telescopes focused Category: Space Tags: CubeSat Laser MIT Space telescope

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04.01.2019
20:44 LiveScience.comLaser-Blasted Plasma Is Colder Than Deep Space...Literally

Laser-cooled plasma has all the chill.

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03.01.2019
06:07 Arxiv.org PhysicsRelativistic laser driven electron accelerator using micro-channel plasma targets. (arXiv:1901.00475v1 [physics.plasm-ph])

We present an experimental demonstration of the efficient acceleration of electrons beyond 60 MeV using micro-channel plasma targets. We employed a high-contrast, 2.5 J, 32 fs short pulse laser interacting with a 5 \mu m inner diameter, 300 \mu m long micro-channel plasma target. The micro-channel was aligned to be collinear with the incident laser pulse, confining the majority of the laser energy within the channel. The measured electron spectrum showed a large increase of the cut-off energy and slope temperature when compared to that from a 2 \mu m flat Copper target, with the cutoff energy enhanced by over 2.6 times and the total energy in electrons >5 MeV enhanced by over 10 times. Three-dimensional particle-in-cell simulations confirm efficient direct laser acceleration enabled by the novel structure as the dominant acceleration mechanism for the high energy electrons. The simulations

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06:07 Arxiv.org PhysicsSelective Delamination upon Femtosecond Laser Ablation of Ceramic Surfaces. (arXiv:1901.00460v1 [physics.app-ph])

We report on the experimental observation of selective delamination of semi-transparent materials on the example of yttria-stabilized zirconia ceramics upon femtosecond laser processing of its surface with low numerical aperture lens. The delamination of a ceramic layer of dozens of micrometers takes place as a by-side effect of surface processing and is observed above the surface ablation threshold. The onset of delamination (delamination threshold) depends on the degree of overlap of the irradiation spots from consecutive laser pulses upon beam scanning over material surface. Analysis of the delaminated layer indicates that the material undergoes melting on its both surfaces. The mechanism of delamination is identified as a complex interplay between the optical response of laser-generated free-electron plasma and nonlinear effects upon laser beam propagation in semi-transparent ceramics.

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01.01.2019
16:49 Ixbt.com Завтра стартуют продажи нового проектора Xiaomi Mi Laser Projector Lite ценой $320

В ассортименте проекторов Xiaomi появилась новая модель - Xiaomi Mi Laser Projector Lite. Завтра она появится на местной китайской платформе коллективного финансирования, и каждый участник программы сможет приобрести ее за эквивалент $320. Ну а когда новинка поступит в розничную продажу, то цена будет уже немного выше – $365.
Mi Laser Projector Lite работает под управлением ОС MIUI TV – аналогичная используется в телевизорах Xiaomi. Устройство оснащено двумя двухдюймовыми громкоговорителями мощностью 10 Вт и поддерживает технологии Dolby Audio и DTS. Также поддерживается технология HDR10, голосовое управление и вывод картинки на экраны диагональю от 80 до 120 дюймов (при разрешении Full HD). В Mi Laser Projector Lite используется лампа OSRAM P1W/A, яркость потока составляет 800 ANSI лм.
Больше подробностей о Mi Laser Projector Lite появится завтра, но уже понятно,

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11:32 Arxiv.org PhysicsBessel-Bessel laser bullets doing the twist. (arXiv:1812.11493v1 [physics.optics])

Bessel beams carry orbital angular momentum (OAM). Opening up of the Hilbert space of OAM for information coding makes Bessel beams potential candidates for utility in data transfer and optical communication. A laser bullet is the ultra-short and tightly-focused analogue of a non-diffracting and non-dispersing laser Bessel beam. Here, we show fully analytically that a Bessel-Bessel laser bullet possesses orbital angular momentum. Analytic investigation of the energy, linear momentum, energy flux, and angular momentum, associated with the fields of a Bessel-Bessel bullet, in an under-dense plasma, is conducted. The expressions reported here will play a crucial role in preparing the laser bullets for practical applications, such as data transfer in optical communication, x- and gamma-ray generation from colliding bullets with counter-propagating electron bunches, particle trapping, tweezing and

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31.12.2018
07:13 Arxiv.org PhysicsIntrapulse Impact Processes in Dense-Gas Femtosecond Laser Filamentation. (arXiv:1812.11171v1 [physics.optics])

The processes of energy gain and redistribution in a dense gas subject to an intense ultrashort laser pulse are investigated theoretically for the case of high-pressure argon. The electrons released via strong-field ionization and driven by oscillating laser field collide with neutral neighbor atoms, thus effecting the energy gain in the emerging electron gas via a short-range inverse Bremsstrahlung interaction. These collisions also cause excitation and impact ionization of the atoms thus reducing the electron-gas energy. A kinetic model of these competing processes is developed which predicts the prevalence of excited atoms over ionized atoms by the end of the laser pulse. The creation of a significant number of excited atoms during the pulse in high-pressure gases is consistent with the delayed ionization dynamics in the pulse wake, recently discovered by Gao et al.[1] This energy

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07:13 Arxiv.org PhysicsDirection and divergence control of laser-driven energetic proton beam using a disk-solenoid target. (arXiv:1812.11121v1 [physics.plasm-ph])

A scheme for controlling the direction of energetic proton beam driven by intense laser pulse is proposed. Simulations show that a precisely directed and collimated proton bunch can be produced by a sub-picosecond laser pulse interacting with a target consisting of a thin solid-density disk foil with a solenoid coil attached to its back at the desired angle. It is found that two partially overlapping sheath fields are induced. As a result, the accelerated protons are directed parallel to the axis of the solenoid, and their spread angle is also reduced by the overlapping sheath fields. The proton properties can thus be controlled by manipulating the solenoid parameters. Such highly directional and collimated energetic protons are useful in the high-energy-density as well as medical sciences.

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07:13 Arxiv.org PhysicsObservations of Coherent Optical Transition Radiation Interference Fringes Generated by Laser Plasma Accelerator Electron Beamlets. (arXiv:1812.10778v1 [physics.acc-ph])

We report initial observations of coherent optical transition radiation interferometry (COTRI) patterns generated by microbunched electrons from laser-driven plasma accelerators (LPAs). These are revealed in the angular distribution patterns obtained by a CCD camera with the optics focused at infinity, or the far-field, viewing a Wartski two-foil interferometer. The beam divergences deduced by comparison to results from an analytical model are sub-mrad, and they are smaller than the ensemble vertical beam divergences measured at the downstream screen of the electron spectrometer. The transverse sizes of the beamlet images were obtained with focus at the object, or near field, and were in the few-micron regime as reported by LaBerge et al. The enhancements in intensity are significant relative to incoherent optical transition radiation (OTR) enabling multiple cameras to view each shot. We

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07:13 Arxiv.org PhysicsSupersymmetric Laser Arrays. (arXiv:1812.10690v1 [physics.optics])

The theoretical framework of supersymmetry (SUSY) aims to relate bosons and fermions -- two profoundly different species of particles -- and their interactions. While this space-time symmetry is seen to provide an elegant solution to many unanswered questions in high-energy physics, its experimental verification has so far remained elusive. Here, we demonstrate that, notions from supersymmetry can be strategically utilized in optics in order to address one of the longstanding challenges in laser science. In this regard, a supersymmetric laser array is realized, capable of emitting exclusively in its fundamental transverse mode. Our results not only pave the way towards devising new schemes for scaling up radiance in integrated lasers, but also on a more fundamental level, they could shed light on the intriguing synergy between non-Hermiticity and supersymmetry.

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07:13 Arxiv.org PhysicsPolarization-insensitive space-selective etching in fused silica induced by picosecond laser irradiation. (arXiv:1812.10661v1 [physics.optics])

It is well known that when the fused silica is irradiated with focused femtosecond laser beams, space selective chemical etching can be achieved. The etching rate depends sensitively on the polarization of the laser. Surprisingly, we observe that by chirping the Fourier-transform-limited femtosecond laser pulses to picosecond pulses, the polarization dependence of the etching rate disappears, whereas an efficient etching rate can still be maintained. Observation with a scanning electron microscope reveals that the chirped pulses can induce interconnected nanocracks in the irradiated areas which facilitates efficient introduction of the etchant into the microchannel. The reported technology is of great use for fabrication of three-dimensional (3D) microfluidic systems and glass-based 3D printing.

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28.12.2018
15:20 Phys.orgLaser diode detects counterfeit olive oil

Researchers at the Complutense University of Madrid (UCM) and the Scintillon Institute in the U.S. have designed a sensor that can detect counterfeit olive oil labeled as extra virgin or protected designation of origin.

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27.12.2018
11:08 Arxiv.org PhysicsObservation of Spider Silk by Femtosecond Pulse Laser Second Harmonic Generation Microscopy. (arXiv:1812.10390v1 [cond-mat.soft])

An asymmetric \b{eta}-sheet structure of spider silk is said to induce optical second harmonic generation. In this paper, using an in-house non-scanning type femtosecond pulse laser second harmonic generation microscope, we characterized the behavior of the \b{eta}-sheet of spider silk under an applied external force. The orientation of the \b{eta}-sheets was more unidirectional when the silk was extended. One of the origins of the high mechanical strength of the dragline is suggested to be the physical arrangement of its \b{eta}-sheets.

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11:08 Arxiv.org PhysicsFast fabrication of optical vortex generators by femtosecond laser ablation. (arXiv:1812.10272v1 [physics.optics])

Fast fabrication of micro-optical elements for generation of optical vortex beams based on the q-plate design is demonstrated by femtosecond (fs) laser ablation of gold film on glass. Q-plates with diameter of ~0.5 mm were made in ~1 min using galvanometric scanners with writing speed of 5 mm/s. Period of gratings of 0.8 micrometers and groove width of 250 nm were achieved using fs-laser ablation at 343 nm wavelength. Phase and intensity analysis of optical vortex generators was carried out at 633 nm wavelength and confirmed the designed performance. Efficiency of spin-orbital conversion of the q-plates made by ablation of 50-nm-thick film of gold was ~3%. Such gratings can withstand thermal annealing up to 800C. They can be used as optical vortex generators using post-selection of polarisation.

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11:08 Arxiv.org PhysicsSelf Modulation and Scattering Instability of a Relativistic Laser Pulse in an Underdense Plasma within a unified Analysis Framework. (arXiv:1812.10106v1 [physics.plasm-ph])

We present a unified analysis framework that simultaneously covers self-modulation and parametric instability of a short, relativistically intense laser pulse propagating inside an underdense plasma. The key point in our approach is formulation of the plasma wave in terms of quantities which become motion constants in the absence of pulse evolutions. This leads to (i) a transparent characterization of the self-consistent plasma evolutions in the presence of laser pulse evolutions and (ii) recovering the simple coupled-oscillator form for field-plasma perturbations, even in the presence of strong initial wakefield. The latter facilitate instability studies in the strongly nonlinear regime. We firstly consider analytical solution of our basic equations, and find new closed results for pulse self-modulation at general conditions. Specially, precise expressions are obtained for spatiotemporal

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11:08 Arxiv.org PhysicsCollisionless absorption of short laser pulses in a deuterium cluster: dependence of redshift of resonance absorption peak on laser polarization, intensity and wavelength. (arXiv:1812.10046v1 [physics.plasm-ph])

We study collisionless absorption of short laser pulses of various intensity, wavelength ($\lambda$) and polarization in a deuterium cluster using molecular dynamics (MD) simulation. For a given laser energy and a pulse duration $\approx$ 5-fs (fwhm), it is found that maximum laser absorption does not happen at the welknown static Mie-resonance or linear resonance (LR) wavelength of $\lambdaM\approx 263$~nm (for deuterium cluster) irrespective of linear polarization (LP) and circular polarization (CP) state of laser. As the laser intensity increases, the absorption peak is gradually red-shifted to a higher $\lambda$ in the marginally over-dense regime of $\lambda\!\! \approx \!\!(1\!\!-\!\!1.5)\lambdaM$ from the expected static~$\lambdaM$ owing to gradual outer ionization and cluster expansion; and above an intensity the resonance absorption peak disappears (sometimes followed by {\em even} a

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11:08 Arxiv.org PhysicsCondensation of laser produced gold plasma during expansion and cooling in water environment. (arXiv:1812.09929v1 [physics.comp-ph])

The ecologically best way to produce nanoparticles (NP) is based on laser ablation in liquid (LAL). In the considered here case the LAL means that a gold target is irradiated through transparent water. During and after irradiation the heated material from surface of a target forms a plume which expands into liquid.
In this paper we study a reach set of physical processes mixed with complicated hydrodynamic phenomena which all accompany LAL. These theoretical and simulation investigations are very important for practical applications. Laser pulses with different durations $\tau_L$ covering 5-th orders of magnitudes range from 0.1 ps to 0.5 ns and large absorbed fluences $F_{abs}$ near optical breakdown of liquid are compared. It is shown that the trajectory of the contact boundary with liquid at the middle and late stages after passing of the instant of maximum intensity of the longest

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11:08 Arxiv.org PhysicsMaskless laser processing of graphene. (arXiv:1812.09839v1 [physics.app-ph])

Graphene on a SiO$_2$/Si substrate was removed by ultraviolet pulsed laser irradiation. Threshold laser power density to remove graphene depended on the graphene thickness. The mechanism is discussed using kinetic energy of thermal expansion of the substrate surface. Utilizing the thickness dependence, thickness (or layer-number) selective process for graphene is demonstrated. Maskless patterning of graphene using laser irradiation in the air is also demonstrated.

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11:08 Arxiv.org PhysicsThomson backscattering in combined uniform magnetic and envelope modulating circularly-polarized laser fields. (arXiv:1812.09690v1 [physics.optics])

The Thomson backscattering spectra in combined uniform magnetic and cosine-envelope circularly-polarized laser fields are studied in detail. With an introduction of the envelope modulation, the radiation spectra exhibit high complexity attributed to the strong nonlinear interactions. On the other hand, four fundamental laws related to the scale invariance of the radiation spectra are analytically revealed and numerically validated. They are the laws for the radiation energy as the $6$th power of the motion constant exactly, also as the approximate negative $6$th power with respect to the initial axial momentum and laser intensity in a certain of conditions, respectively, and finally an important self-similar law, i.e., when the circular laser frequency, the envelope modulation frequency, and the modified cyclotron frequency are simultaneously increased by a factor, the radiation energy will

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11:08 Arxiv.org PhysicsAngle-Resolved Spectra of the Direct Above-Threshold Ionization of Diatomic Molecule in IR+XUV laser field. (arXiv:1812.09634v1 [physics.atom-ph])

The direct above-threshold ionization (ATI) of diatomic molecules in linearly-polarized infrared and extreme ultraviolet (IR+XUV) laser fields is investigated by the frequency-domain theory based on the nonperturbative quantum electrodynamics. The destructive interference fringes on the angle-resolved ATI spectra, which are closely related to the molecular structure, can be well fitted by a simple predictive formula for any alignment of the molecular axis. By comparing the direct ATI spectra for monochromatic and two-color laser fields, we found that the XUV laser field can both raise the ionization probability and the kinetic energy of the ionized electron, while the IR laser field can broaden the energy distribution of the ionized electron. Our results demonstrate that, by using IR+XUV two-color laser fields, the angle-resolved spectra of the direct ATI can image the structural information

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11:08 Arxiv.org PhysicsLaser Amplification in Strongly-Magnetized Plasma. (arXiv:1812.09429v1 [physics.plasm-ph])

We consider backscattering of laser pulses in strongly-magnetized plasma mediated by kinetic magnetohydrodynamic waves. Magnetized low-frequency scattering, which can occur when the external magnetic field is neither perpendicular nor parallel to the laser propagation direction, provides an instability growth rate higher than Raman scattering and a frequency downshift comparable to Brillouin scattering. In addition to the high growth rate, which allows smaller plasmas, and the 0.1-2\% frequency downshift, which permits a wide range of pump sources, MLF scattering is an ideal candidate for amplification because the process supports an extremely large bandwidth, which particle-in-cell simulations show produces ultrashort durations. Under some conditions, MLF scattering also becomes the dominant spontaneous backscatter instability, with implications for magnetized laser-confinement

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24.12.2018
05:06 Arxiv.org PhysicsLaser-induced Phase-change Perovskite Photodetector Arrays for Optical Information Storage and Imaging. (arXiv:1812.09267v1 [physics.app-ph])

The reversible phase transition between orthorhombic and cubic phases is demonstrated in all-inorganic perovskite CsPbIBr2 grown by a dual-source vapor-deposition method. The phase transition is actuated via heating and moisture exposure. The different crystal structures of two phases result in distinct optoelectronic properties including optical absorption, refractive index, and carrier transport. The perovskite photodetector array for the non-volatile rewritable optical memory application is further investigated. A near-infrared (NIR) laser ({\lambda} = 1064 nm) is used to selectively heat photodetector pixels through the photothermal effect of the interfacial Ag electrodes, resulting in an optically absorbing perovskite phase for the photodetectors. The locations of specific laser-written pixels can be read out by measuring their photocurrents, and the stored optical information can also

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05:06 Arxiv.org PhysicsJoule-level high effiency energy transfer to sub-picosecond laser pulses by a plasma-based amplifier. (arXiv:1812.09229v1 [physics.plasm-ph])

Laser plasma amplification of sub-picosecond pulses above the Joule level is demonstrated, a major milestone for this scheme to become a solution for the next-generation of ultra-high intensity lasers. By exploring over 6 orders of magnitude the influence of the incident seed intensity on Brillouin laser amplification, we reveal the importance of a minimum intensity to ensure an early onset of the self-similar regime, and a large energy transfer with a very high efficiency, up to 20%. Evidence of energy losses of the seed by spontaneous backward Raman is found at high amplification. The first three-dimensional envelope simulations of the sub-picosecond amplification were performed, supplemented by one-dimensional PIC simulations. Comparisons with the experimental results demonstrate the capability of quantitative predictions on the transferred energy. The global behavior of the

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05:06 Arxiv.org PhysicsLaser-induced ablation of metal in liquid. (arXiv:1812.09109v1 [physics.comp-ph])

Laser ablation in liquid (LAL) is important perspective way to compose nanoparticles (NP) necessary for modern technologies. LAL is not fully understood. Deep understanding is necessary to optimize processes and decrease high price of the LAL NPs.
Today there are two groups of studies: in one of them scientists go from analyzing of bubble dynamics (thus they proceed from the late stages), while in another one scientists investigate early stages of ablation. In the present paper we consider the process as whole: from ablation and up to formation of a bubble and its inflation. Thus we cover extremely wide range of spatiotemporal scales. We consider role of absorbed energy and duration of pulse (femtosecond, multi-picosecond, nanosecond). Importance of supercritical states is emphasized. Diffusive atomic and hydrodynamic mixing due to Rayleigh-Taylor instability and their mutual

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22.12.2018
02:14 ScienceDaily.comLaser diode combats counterfeit oil

The olive oil sector has witnessed a rise in fraudulent activities such as falsely labeling inferior products as high quality. To combat this practice, a research team has developed a tool based on laser diodes and chaotic algorithms to detect whether the label on a bottle corresponds or not to the content inside.

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21.12.2018
23:35 ExtremeTech.comLG’s New Laser Projector Works Just 2 Inches Away From Your Wall

The days of mounting the projector in the middle of your space have come to an end with the advent of ultra short throw (UST) projectors. These devices can sit closer to the projection surface, and LG's new CineBeam Laser 4K projector gets closer than ever.
The post LG’s New Laser Projector Works Just 2 Inches Away From Your Wall appeared first on ExtremeTech.

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15:24 Zdnet.comLaser-equipped drones capture epic 3D scan of hulking battleship

Navigating "the pit of death" and hydraulic oil, a team of tinkerers renders a stunning point cloud in this challenging virtualization.

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14:56 Ixbt.com Проектор LG CineBeam Laser 4K выводит изображение диагональю 120" с расстояния 18 см

Южнокорейская компания LG Electronics на этой неделе представила нового представителя линейки проекторов CineBeam Laser 4K, который получил модельный номер HU85L.
Особенностью модели является возможность вывода изображения большой диагонали с небольшого расстояния. Проектор LG CineBeam Laser 4K HU85L позволяет отобразить картинку диагональю 120 дюймов с расстояния 17,8 см.
Проектор поддерживает вывод изображения разрешением 3840 х 2160 пикселей, при этом яркость изображения составляет 2500 ANSI-люменов. При расстоянии от стены всего 5 см диагональ формируемого изображения достигает 90 дюймов.
Производитель заявляет, что проектор отличается глубоким черным цветом и точностью отображения информации. Кроме того, пульт управления Magic Remote поддерживает управления жестами и голосовые команды.
В перечне портов есть USB, Ethernet и HDMI. К сожалению, информации о сроках выпуска

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10:31 3dnewsНовый проектор LG CineBeam Laser 4K создаёт 120" изображение с расстояния менее 20 см

Компания LG Electronics (LG) представила новый проектор CineBeam Laser 4K, познакомиться с которым смогут посетители грядущей выставки Consumer Electronics Show (CES) 2019. Лазерное устройство (модель HU85L) выполнено с применением технологии Ultra Short Throw (UST). Проектор способен формировать изображение размером 90 дюймов по диагонали с расстояния немногим более двух дюймов (5 см) до экрана. При увеличении расстояния до 7 дюймов (примерно 18 см) размер картинки возрастает до 120 дюймов по диагонали.

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06:22 Arxiv.org PhysicsSpectral intensity and phase changes of short laser pulses by two-photon absorption. (arXiv:1812.08573v1 [physics.optics])

We calculated third order non-linear polarization to estimate the two-photon absorption of non-interacting two-level molecules in the transmission-type degenerate pump-probe geometry. The spectral intensity and the phase changes of the laser pulses when passing through a thin dielectric slab composed of the molecules were considered. We also investigated the effect of the decay rate of the molecules and the chirp of the pulses on their spectral intensity and phase changes.

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06:22 Arxiv.org PhysicsSwept-Wavelength Mid-Infrared Fiber Laser for Real-Time Ammonia Gas Sensing. (arXiv:1812.08298v1 [physics.ins-det])

The mid-infrared (mid-IR) spectral region holds great promise for new laser-based sensing technologies, based on measuring strong mid-IR molecular absorption features. Practical applications have been limited to date, however, by current low-brightness broadband mid-IR light sources and slow acquisition-time detection systems. Here, we report a new approach by developing a swept-wavelength mid-infrared fiber laser, exploiting the broad emission of dysprosium and using an acousto-optic tunable filter to achieve electronically controlled swept-wavelength operation from 2.89 to 3.25 {\mu}m (3070-3460 cm^-1). Ammonia (NH3) absorption spectroscopy is demonstrated using this swept source with a simple room-temperature single-pixel detector, with 0.3 nm resolution and 40 ms acquisition time. This creates new opportunities for real-time high-sensitivity remote sensing using simple, compact mid-IR

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06:22 Arxiv.org PhysicsOn-chip Rotated Polarization Directional Coupler Fabricated by Femtosecond Laser Direct Writing. (arXiv:1812.08240v1 [quant-ph])

We present a rotated polarization directional coupler (RPDC) on a photonic chip. We demonstrate a double-track approach to modify the distribution of refractive index between adjacent tracks and form a single waveguide with arbitrary birefringent optical axis. We construct a RPDC with the two axis-rotated waveguides coupled in a strong regime. The obtained extinction ratios on average are about 16dB and 20dB for the corresponding orthogonal polarizations. We perform the reconstruction of Stokes vector to test the projection performance of our RPDC, and observe the average fidelities up to 98.1% and 96.0% for the perfectly initialized states in 0$^\circ$ and 45$^\circ$ RPDCs respectively.

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20.12.2018
09:12 Arxiv.org PhysicsDeep laser cooling and efficient magnetic compression of molecules. (arXiv:1812.07926v1 [physics.atom-ph])

We introduce a scheme for deep laser cooling of molecules based on optical pumping into robust dark states at zero velocity. Using multi-level optical Bloch equations to simulate this scheme, we show that it may be feasible to reach the recoil limit or below. We demonstrate and characterise the method experimentally, reaching a temperature of 5.8(5) {\mu}K. We measure the complete velocity distribution directly, by rotating the phase-space distribution and then imaging the cloud. Using the same phase-space rotation method, we rapidly compress the cloud. By applying the cooling method a second time, we compress both the position and velocity distributions.

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09:12 Arxiv.org PhysicsGoldilocks Zone for Enhanced Ionization in Strong Laser Fields. (arXiv:1812.07758v1 [physics.atom-ph])

Utilizing a benchmark measurement of laser-induced ionization of an H$_2^+$ molecular ion beam target at infrared wavelength around 2 $\mu$m, we show that the characteristic two-peak structure predicted for laser-induced enhanced ionization of H$_2^+$ and diatomic molecules in general, is a phenomenon which is confined to a small laser parameter space --- a Goldilocks Zone. Further, we control the effect experimentally and measure its imprint on the electron momentum. We replicate the behavior with simulations, which reproduce the measured kinetic-energy release as well as the correlated-electron spectra. Based on this, a model, which both maps out the Goldilocks Zone and illustrates why enhanced ionization has proven so elusive in H$_2^+$, is derived.

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19.12.2018
15:48 Phys.orgFocus on this: Team increases X-ray laser focusing ability

An X-ray free-electron laser (XFEL) is an X-ray produced by a beam of free electrons that have been accelerated almost to the speed of light. XFELs produce laser beams with exceedingly high peak power intensity, which makes them attractive for applications in fundamental research, such as X-ray nonlinear optics and protein crystal structure determination, and also in medicine. It is important to precisely focus XFEL beams to achieve high performance. Lasers are typically focused using total reflection mirrors; however, conventional mirrors are unsuitable for formation of sub-10 nm X-ray beams because such mirrors cannot deliver the large numerical aperture required. To overcome this limitation, X-ray beams can be focused using multilayer mirrors. Unfortunately, it is difficult to manufacture such multilayer mirrors because very high fabrication accuracy is required.

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04:59 Arxiv.org PhysicsUltrarelativistic electron beam polarization in single-shot interaction with an ultraintense laser pulse. (arXiv:1812.07229v1 [physics.plasm-ph])

Spin-polarization of an ultrarelativistic electron beam head-on colliding with an ultraintense laser pulse is investigated in the quantum radiation-reaction regime. We develop a Monte-Carlo method to model electron radiative spin effects in arbitrary electromagnetic fields by employing spin-resolved radiation probabilities in the local constant field approximation. Due to spin-dependent radiation reaction, the applied elliptically polarized laser pulse polarizes the initially unpolarized electron beam and splits it along the propagation direction into two oppositely transversely polarized parts with a splitting angle of about tens of milliradians. Thus, a dense electron beam with above 70\% polarization can be generated in tens of femtoseconds. The proposed method demonstrates a way for relativistic electron beam polarization with currently achievable laser facilities.

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18.12.2018
07:37 Arxiv.org PhysicsSimulation of Hot-Carrier Dynamics and Terahertz Emission in Laser-Excited Metallic Bilayers. (arXiv:1812.06892v1 [physics.app-ph])

Metallic bilayer structures have been shown to emit strong terahertz (THz) pulses. We present a predictive multiscale mode that simulates optically induced spin-currents in a Fe/Pt-heterostructure and the emitted electric field. Electronic effects are treated on the nano scale using the Boltzmann transport equation for the dynamics of out-of-equilibrium charge carriers, numerically solved with a particle-in-cell code. The optical effects are simulated with a formalism that bridges the nanometer scale of the structure to the micrometer scale of the emitted waves. The approach helps to understand recent experimental findings on the basis of microscopic scattering effects and transport phenomena. Our theory's versatility allows it to be readily adapted to a wide spectrum of spintronic THz emitter designs. As an example, we show how the THz generation efficiency, defined as output to input power

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07:37 Arxiv.org PhysicsTricks of the light: the remarkable power of laser tweezers to dissect complex biological questions. (arXiv:1812.06517v1 [physics.bio-ph])

On 2 October 2018 Goran Hansson, Secretary General of the Royal Swedish Academy of Sciences, announced that the Nobel Prize in Physics would be jointly awarded to Arthur Ashkin, Gerard Mourou and Donna Strickland, for their groundbreaking inventions in the field of laser physics. Strickland and Mourou shared one half of the prize for their pioneering work in generating high-intensity, ultra-short optical pulses. The recipient of the other half was Arthur Ashkin for his seminal work leading to the development of optical tweezers, also referred to as optical traps or laser tweezers, and their applications to an enormous range of biological systems. As discussed below, laser tweezers are a remarkable class of optical force transduction tools which have had a profound effect in enabling several complex biological questions to be addressed impenetrable using other existing

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07:37 Arxiv.org PhysicsEmploying machine learning for theory validation and identification of experimental conditions in laser-plasma physics. (arXiv:1812.06304v1 [physics.plasm-ph])

The validation of a theory is commonly based on appealing to clearly distinguishable and describable features in properly reduced experimental data, while the use of ab-initio simulation for interpreting experimental data typically requires complete knowledge about initial conditions and parameters. We here apply the methodology of using machine learning for overcoming these natural limitations. We outline some basic universal ideas and show how we can use them to resolve long-standing theoretical and experimental difficulties in the problem of high-intensity laser-plasma interactions. In particular we show how an artificial neural network can "read" features imprinted in laser-plasma harmonic spectra that are currently analysed with spectral interferometry.

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17.12.2018
10:18 Arxiv.org PhysicsHelium load on W-O coatings grown by pulsed laser deposition. (arXiv:1812.05714v1 [physics.app-ph])

W-O deposits with complex morphologies and significant He contents will growth on the surface of plasma facing components exposed to He discharges. To mimic the re/co-deposition process, W-O-He coatings were produced by implanting He+ ions on W films grown by pulsed laser deposition (PLD). The use of appropriate PLD experimental parameters such as Ar or He background atmospheres induces the deposition of porous or amorphous-like W-O structures, respectively. After multiple ion implantation stages using 150 keV, 100 keV and 50 keV incident He+ ion beams with a total fluence of 5 x 1017 ion/cm^2, significant amounts of He were identified in porous coatings by Rutherford backscattering (RBS). Time-of-flight elastic recoil detection (TOF-ERDA) measurements showed that most of the implanted He was already released from the porous coatings five month after implantation while for the case of

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10:18 Arxiv.org PhysicsDetermination of CaOH and CaOCH$_3$ vibrational branching ratios for direct laser cooling and trapping. (arXiv:1812.05636v1 [physics.atom-ph])

Alkaline earth monoalkoxide free radicals (MORs) have molecular properties conducive to direct laser cooling to sub-millikelvin temperatures. Using dispersed laser induced fluorescence (DLIF) measurements from a pulsed supersonic molecular beam source we determine vibrational branching ratios and Franck-Condon factors for the MORs CaOH and CaOCH$_{3}$. With narrow linewidth continuous-wave dye laser excitation, we precisely measure fluorescence branching for both $\tilde{X}-\tilde{A}$ and $\tilde{X}-\tilde{B}$ electronic systems in each molecule. Weak symmetry-forbidden decays to excited bending states with non-zero vibrational angular momentum are observed. Normal mode theoretical analysis combined with ab initio structural calculations are performed and compared to experimental results. Our measurements and analysis pave the way for direct laser cooling of these (and other) complex

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16.12.2018
15:09 Phys.orgLaser-pointing system could help tiny satellites transmit data to Earth

A new laser-pointing platform developed at MIT may help launch miniature satellites into the high-rate data game.

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14.12.2018
17:01 Phys.orgExactly how we would send our first laser-powered probe to Alpha Centauri

The dream of traveling to another star system, and maybe even finding populated worlds there, is one that has preoccupied humanity for many generations. But it was not until the era of space exploration that scientists have been able to investigate various methods for making an interstellar journey. While many theoretical designs have been proposed over the years, a lot of attention lately has been focused on laser-propelled interstellar probes.

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11:51 Arxiv.org PhysicsDirect laser acceleration of electrons by tightly focused laser pulses. (arXiv:1812.05209v1 [physics.plasm-ph])

We present an analytical theory that reveals the importance of the longitudinal laser electric field in the resonant acceleration of relativistic electrons by the tightly confined laser beam. It is shown that this field always counterworks to the laser transverse component and effectively decreases the final energy gain of electrons through direct laser acceleration mechanism. This effect is demonstrated by carrying out the particle-in-cell simulations in the setup where the wakefield in the plasma bubble is compensated by the longitudinal laser electric field experienced by the accelerated electrons. The derived scalings and estimates are in good agreement with numerical simulations.

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12.12.2018
18:01 Phys.orgMapping the big blue: Laser-induced technology to help mineral exploration at oceanic depths

Scientists have successfully measured zinc samples under deep-sea conditions. Their method could support sustainable extraction of raw seabed materials.

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10:18 Arxiv.org PhysicsLaser control of the electron wave function in transmission electron microscopy. (arXiv:1812.04596v1 [quant-ph])

Laser-based preparation, manipulation, and readout of the states of quantum particles has become a powerful research tool that has enabled the most precise measurements of time, fundamental constants, and electromagnetic fields. Laser control of free electrons can improve the detection of electrons' interaction with material objects, thereby advancing the exploration of matter on the atomic scale. For example, temporal modulation of electron waves with light has enabled the study of transient processes with attosecond resolution. In contrast, laser-based spatial shaping of the electron wave function has not yet been realized, even though it could be harnessed to probe radiation-sensitive systems, such as biological macromolecules, at the standard quantum limit and beyond. Here, we demonstrate laser control of the spatial phase profile of the electron wave function and apply it to enhance

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10:18 Arxiv.org PhysicsLaser Ablation and Injection Moulding as Techniques for Producing Micro Channels Compatible with Small Angle X-Ray Scattering. (arXiv:1812.04568v1 [physics.app-ph])

Microfluidic mixing is an important means for in-situ sample preparation and handling while Small Angle X-Ray Scattering (SAXS) is a proven tool for characterising (macro-)molecular structures. In combination those two techniques enable investigations of fast reactions with high time resolution (<1 ms). The goal of combining a micro mixer with SAXS, however, puts constraints on the materials and production methods used in the device fabrication. The measurement channel of the mixer needs good x-ray transparency and a low scattering background. While both depend on the material used, the requirement for low scattering especially limits the techniques suitable for producing the mixer, as the fabrication process can induce molecular orientations and stresses that can adversely influence the scattering signal. Not only is it important to find a production method that results in a device with

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10:18 Arxiv.org PhysicsHigh-channel-count 20 GHz passively mode locked quantum dot laser directly grown on Si with 4.1 Tbit/s transmission capacity. (arXiv:1812.04550v1 [physics.optics])

Low cost, small footprint, highly efficient and mass producible on-chip wavelength-division-multiplexing (WDM) light sources are key components in future silicon electronic and photonic integrated circuits (EPICs) which can fulfill the rapidly increasing bandwidth and lower energy per bit requirements. We present here, for the first time, a low noise high-channel-count 20 GHz passively mode-locked quantum dot laser grown on complementary metal-oxide-semiconductor compatible on-axis (001) silicon substrate. The laser demonstrates a wide mode-locking regime in the O-band. A record low timing jitter value of 82.7 fs (4 - 80 MHz) and a narrow RF 3-dB linewidth of 1.8 kHz are measured. The 3 dB optical bandwidth of the comb is 6.1 nm (containing 58 lines, with 80 lines within the 10 dB bandwidth). The integrated average relative intensity noise values of the whole spectrum and a single wavelength

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10:18 Arxiv.org PhysicsRotation of polarization in the gravitational field of a laser beam - Faraday effect and optical activity. (arXiv:1812.04505v1 [gr-qc])

We investigate the rotation of the polarization of a light ray propagating in the gravitational field of a circularly polarized laser beam. The rotation consists of a reciprocal part due to gravitational optical activity, and a non-reciprocal part due to the gravitational Faraday effect. We discuss how to distinguish the two effects: Letting light propagate back and forth between two mirrors, the rotation due to gravitational optical activity cancels while the rotation due to the gravitational Faraday effect accumulates. In contrast, the rotation due to both effects accumulates in a ring cavity and a situation can be created in which gravitational optical activity dominates. Such setups amplify the effects by up to five orders of magnitude, which however is not enough to make them measurable with state of the art technology. The effects are of conceptual interest as they reveal

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11.12.2018
20:40 ScienceDaily.comTerahertz laser for sensing and imaging outperforms its predecessors

A new terahertz laser is the first to reach three key performance goals at once -- high constant power, tight beam pattern, and broad electric frequency tuning -- and could thus be valuable for a wide range of applications in chemical sensing and imaging.

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18:07 BBC HealthLaser pointers should be thrown away, say safety experts

Parents are being warned that their children's eyesight could be at risk.

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15:46 Phys.orgTerahertz laser for sensing and imaging outperforms its predecessors

A terahertz laser designed by MIT researchers is the first to reach three key performance goals at once—high constant power, tight beam pattern, and broad electric frequency tuning—and could thus be valuable for a wide range of applications in chemical sensing and imaging.

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15:34 Phys.orgNovel laser technology for microchip-size chemical sensors

Most lasers emit photons of exactly the same wavelength, producing a single color. However, there are also lasers that consist of many frequencies, with equal intervals in between, as in the teeth of a comb; thus, they are referred to as "frequency combs." Frequency combs are perfect for detecting a variety of chemical substances.

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10:37 Technology.orgTerahertz laser for sensing and imaging outperforms its predecessors

A terahertz laser designed by MIT researchers is the first to reach three key performance goals at once

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05:51 Arxiv.org PhysicsSub-Doppler laser cooling of 23Na in gray molasses on the D2 line. (arXiv:1803.05108v2 [cond-mat.quant-gas] UPDATED)

We report on the efficient gray molasses cooling of sodium atoms using the $D_{2}$ optical transition at 589.1 nm. Thanks to the hyperfine split about 6$\Gamma$ between the $|F'=2\rangle$ and $|F'=3\rangle$ in the excited state 3$^{2}P_{3/2}$, this atomic transition is effective for the gray molasses cooling mechanism. Using this cooling technique, the atomic sample in $F = 2$ ground manifold is cooled from 700 $\upmu$K to 56 $\upmu$K in 3.5 ms. We observe that the loading efficiency into magnetic trap is increased due to the lower temperature and high phase space density of atomic cloud after gray molasses. This technique offers a promising route for the fast cooling of the sodium atoms in the $F=2$ state.

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05:51 Arxiv.org PhysicsSemiconductor laser mode locking stabilization with optical feedback from a silicon PIC. (arXiv:1812.03811v1 [physics.app-ph])

Semiconductor mode-locked lasers can be used in a variety of applications ranging from multi-carrier sources for WDM communication systems to time base references for metrology systems. Their packaging in compact chip- or module-level systems remains however burdened by their strong sensitivity to back-reflections, quickly destroying the coherence of the mode-locking. Here, we investigate the stabilization of mode-locked lasers directly edge coupled to a silicon photonic integrated circuit, with the objective of moving isolators downstream to the output of the photonic circuit. A 2.77 kHz RF linewidth, substantially improved compared to the 15.01 kHz of the free running laser, is obtained. Even in presence of detrimental reflections from the photonic circuit, substantial linewidth reductions from 20 kHz to 8.82 kHz, as well as from ~300 kHz to 14.8 kHz, are realized.

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05:51 Arxiv.org PhysicsPhotonic Flatband Laser. (arXiv:1812.03356v1 [physics.optics])

Flatband photonic lattices, i.e. arrays of waveguides or resonators displaying a flat Bloch band, offer new routes for light trapping and distortion-free imaging. Here it is shown that flatland lattices can show stable and cooperative laser emission when optical gain is supplied to the system, despite the large degree of degeneracy of flatland supermodes. By considering a quasi one-dimensional rhombic lattice of coupled semiconductor microrings, selective pumping of the outer sublattices can induce cooperative lasing in a supermode of the flat band

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10.12.2018
21:30 WhatReallyHappened.comWatch: New Video Surfaces Of Russian Combat Laser As US Threatens To Abandoned INF Treaty 

Secretary of State Mike Pompeo made it clear Tuesday that the US will stop adhering to the Intermediate-Range Nuclear Forces Treaty (INF) in 60 days unless Russia "returns to full and verifiable compliance."
That move sparked a deepening in the Cold War 2.0, as a new video was published Wednesday in Russian state media reminding the West, Russia possess advanced weaponry, like its latest laser combat system.

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20:39 ScienceDaily.comNovel laser technology for microchip-size chemical sensors

A special laser system has been developed, using two slightly different frequency combs. This allows for chemical analysis on tiny spaces -- it is a millimeter-format chemistry lab. With this new patent-pending technology, frequency combs can be created on a single chip in a very simple and robust manner.

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19:56 Nanowerk.comNovel laser technology for microchip-size chemical sensors

Frequency combs are optimally suited for chemical sensors; a revolutionary technology now produces these laser frequencies in a much easier and more robust way.

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08:36 Arxiv.org PhysicsLaser-assisted generation of elongated Au nanoparticles and subsequent dynamics of their morphology under pulsed irradiation in water and calcium chloride solutions. (arXiv:1812.03041v1 [physics.gen-ph])

One-step laser generation of Au elongated nanoparticles (NPs) and their successive fragmentation and agglomeration are experimentally studied for the first time. In the present work, laser-assisted formation of Au elongated nanoparticles by ablation of a solid Au (99.99%) target in water was done using a ytterbium-doped fiber laser sources with pulse duration of 200 ns and pulse energy of 1mJ. Extinction spectrum correlating with TEM shows the appearance of absorption signal in red region and near IR-spectrum that corresponds to longitudinal plasmon resonance of electrons in elongated Au NPs. In addition, generated elongated Au nanoparticles were exposed to pulsed laser beam with various pulse energy and laser exposure time. It was found that at early stages of irradiation NPs agglomerate as the NPs chains with size of order of 1 micrometer long. Further laser exposure results in

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08:36 Arxiv.org PhysicsSpontaneous laser line sweeping in bi-directional ring thulium fiber laser. (arXiv:1812.02929v1 [physics.optics])

We report a phenomenon of self-sweeping in a bi-directional ring thulium-doped fiber laser, for the first time. The laser is spontaneously sweeping in both directions at a rate up to 0.2 nm/s with 15 nm sweeping range in 1.95 {\mu}m wavelength region. The laser output is switchable between two different working modes: periodical spontaneous laser line sweeping with generation of microsecond pulses in time domain; or static central wavelength with amplitude modulated temporally.

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08:36 Arxiv.org PhysicsLaser-cooled caesium atoms confined with magic-wavelength dipole inside a hollow-core photonic-bandgap fiber. (arXiv:1812.02887v1 [physics.atom-ph])

We report loading of laser-cooled caesium atoms into a hollow-core photonic-bandgap fiber and confining the atoms in the fiber's 7 $\mu m$ diameter core with a magic-wavelength dipole trap at $\sim$935 nm. The use of the magic wavelength removes the AC-Stark shift of the 852nm optical transition in caesium caused by the dipole trap in the fiber core and suppresses the inhomogeneous broadening of the atomic ensemble that arises from the radial distribution of the atoms. This opens the possibility to continuously probe the atoms over time scales of a millisecond -- approximately 1000 times longer than what was reported in previous works, as dipole trap does not have to be modulated. We describe our atom loading setup and its unique features and present spectroscopy measurements of the caesium's D$_{2}$ line in the continuous wave dipole trap with up to $1.7 \times 10^{4}$ loaded inside the

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07.12.2018
09:30 Arxiv.org PhysicsNuclear Isomer Excitation in 229Th Atom by Super-Intense Laser Field. (arXiv:1812.02484v1 [physics.optics])

Excitation of the isomeric nuclear state 229m Th in the process of thorium atom irradiation by two-color femtosecond pulse of Ti: Sa laser at the fundamental wavelength and second harmonic is analyzed. It is shown that the rate of isomeric state excitation can be enhanced significantly with respect to other nucleus excitation processes in laser plasma or by an external coherent source at the resonance wavelength. This enhancement is due to the process of nonlinear laser nuclear excitation based on the following. First, the atomic current associated with the motion of valence electrons in strong field is a nonlinear function of the field amplitude. Secondly, the energy of photons at frequency of the Ti:Sa laser fifth harmonic coincides with the energy of the 229m Th state. Yield of this harmonic is much higher if the two-color (1st and 2nd harmonics of the fundamental) is used. Thirdly, the

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06.12.2018
05:09 Arxiv.org PhysicsLaser Mode Bifurcations Induced by $\mathcal{PT}$-Breaking Exceptional Points. (arXiv:1812.01872v1 [physics.optics])

A laser consisting of two independently-pumped resonators can exhibit mode bifurcations that evolve out of the exceptional points (EPs) of the linear system at threshold. The EPs are non-Hermitian degeneracies occurring at the parity/time-reversal ($\mathcal{PT}$) symmetry breaking points of the threshold system. Above threshold, the EPs become bifurcations of the nonlinear zero-detuned laser modes, which can be most easily observed by making the gain saturation intensities in the two resonators substantially different. Small pump variations can then switch abruptly between different laser behaviors, e.g. between below-threshold and $\mathcal{PT}$-broken single-mode operation.

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05.12.2018
22:52 ScienceMag.orgSpace laser will map Earth’s forests in 3D, spotting habitat for at-risk species

NASA’s GEDI mission will also track stored carbon and the impact of forests on climate change

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07:56 Arxiv.org PhysicsNonreciprocal Phonon Laser. (arXiv:1810.08761v2 [quant-ph] UPDATED)

We propose nonreciprocal phonon lasing in a coupled cavity system composed of an optomechanical and a spinning resonator. We show that the optical Sagnac effect leads to significant modifications in both the mechanical gain and the power threshold for phonon lasing. More importantly, the phonon lasing in this system is unidirectional, that is the phonon lasing takes place when the coupled system is driven in one direction but not the other. Our work establishes the potential of spinning optomechanical devices for low-power mechanical isolation and unidirectional amplification. This provides a new route, well within the reach of current experimental abilities, to operate cavity optomechanics devices for such a wide range of applications as directional phonon switches, invisible sound sensing, and topological or chiral acoustics.

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07:56 Arxiv.org PhysicsJoint analysis of two-way laser range and one-way frequency measurements for the gravitational redshift experiment with the RadioAstron spacecraft. (arXiv:1812.01578v1 [physics.space-ph])

We consider the problem of joint analysis of two-way laser range and one-way frequency measurements in high-precision tests of general relativity with spacecrafts. Of main interest to such tests is the accuracy of the computed values of the one-way frequency observables. We identify the principal sources of error in these observables to be the errors in the modeled corrections due to various `small' effects, such as that of the troposphere, the error in the reflection time of the laser pulse from the spacecraft, and the error of fitting the spacecraft trajectory to the laser data. We suggest ways to evaluating these errors.

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07:56 Arxiv.org PhysicsTwo and three photon excited luminescence of single gold nanoparticles: Switching between plasmon- and electron-hole-pair emission by ultrashort laser pulses. (arXiv:1812.01409v1 [physics.optics])

In this work we use femtosecond laser pulses of 800 nm wavelength to excite and characterize the multiphoton luminescence emission of single gold nanoparticles. For excitation with 100 fs laser pulses we observe a two and three photon emission dominated by radiative electron hole pair recombination, while the emission is caused by radiative plasmon decay for excitation with 500 fs pulses. For single gold nanorods with different aspect ratios, we study the interplay between the particle plasmon and electron hole pairs, which enables us to develop a quantitative model to fully describe the two and three photon luminescence emission of single gold nanoparticles.

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07:56 Arxiv.org PhysicsA new energy spectrum reconstruction method for Time-Of-Flight diagnostics of high-energy laser-driven protons. (arXiv:1812.01357v1 [physics.acc-ph])

The Time-of-Flight (ToF) technique coupled with semiconductor-like detectors, as silicon carbide and diamond, is one of the most promising diagnostic methods for high-energy, high repetition rate, laser-accelerated ions allowing a full on-line beam spectral characterization. A new analysis method for reconstructing the energy spectrum of high-energy laser-driven ion beams from TOF signals is hereby presented and discussed. The proposed method takes into account the detector's working principle, through the accurate calculation of the energy loss in the detector active layer, using Monte Carlo simulations. The analysis method was validated against well-established diagnostics, such as the Thomson Parabola Spectrometer, during an experimental campaign carried out at the Rutherford Appleton Laboratory (RAL, UK) with the high-energy laser-driven protons accelerated by the VULCAN Petawatt

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07:56 Arxiv.org PhysicsAnalyzing a single-laser repumping scheme for efficient loading of a strontium magneto-optical trap. (arXiv:1812.01258v1 [physics.atom-ph])

We demonstrate enhanced loading of strontium atoms into a magneto-optical trap using a repumping scheme from the metastable state via the doubly-excited state $5\mathrm{s}5\mathrm{p}\,^3\mathrm{P}_2 \rightarrow 5\mathrm{p}^2\,^3\mathrm{P}_2$. The number of trapped atoms is increased by an order of magnitude. The frequency and intensity dependence of the loading enhancement is well reproduced by a simple rate equation model, which also describes single-laser repumping schemes reported previously. The repumping scheme is limited by a weak additional loss channel into the long-lived $5\mathrm{p}^2\,^3\mathrm{P}_0$ state. For low repumping intensities, the signature of a halo formed by magnetically trapped atoms in the metastable state is found.

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07:56 Arxiv.org CSFeasibility of Colon Cancer Detection in Confocal Laser Microscopy Images Using Convolution Neural Networks. (arXiv:1812.01464v1 [cs.CV])

Histological evaluation of tissue samples is a typical approach to identify colorectal cancer metastases in the peritoneum. For immediate assessment, reliable and real-time in-vivo imaging would be required. For example, intraoperative confocal laser microscopy has been shown to be suitable for distinguishing organs and also malignant and benign tissue. So far, the analysis is done by human experts. We investigate the feasibility of automatic colon cancer classification from confocal laser microscopy images using deep learning models. We overcome very small dataset sizes through transfer learning with state-of-the-art architectures. We achieve an accuracy of 89.1% for cancer detection in the peritoneum which indicates viability as an intraoperative decision support system.

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04.12.2018
10:42 Arxiv.org PhysicsReal-time programmable mode-locked fiber laser with a human-like algorithm. (arXiv:1812.00796v1 [physics.ins-det])

Nonlinear polarized evolution-based passively mode-locked fiber lasers with ultrafast and high peak power pulses are a powerful tool for engineering applications and research. However, their sensitivity to polarization limits their widespread application. To address this, automatic mode-locking immune to environmental disturbances is attracting more concerns. An experimental demonstration of the first real-time programmable mode-locked fiber laser is presented, which is enabled by our proposed human-like algorithm. It combines human logic with a machine's speed, computing capability, and precision. The laser automatically locks onto multiple operation regimes such as fundamental mode-locking, harmonic mode-locking, Q-switching, and even Q-switched mode-locking without physically altering its structure. The average initial mode-locking times (with randomly-assigned original polarization states

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03.12.2018
06:15 Arxiv.org PhysicsLaser-particle collider for multi-GeV photon production. (arXiv:1811.12918v1 [physics.plasm-ph])

As an alternative to Compton backscattering and bremsstrahlung, the process of colliding high-energy electron beams with strong laser fields can more efficiently provide both cleaner and brighter source of photons in the multi-GeV range for fundamental studies in nuclear and quark-gluon physics. In order to favor the emission of high-energy quanta and minimize their decay into electron-positron pairs the fields must not only be sufficiently strong, but also well localized. We here examine these aspects and develop the concept of a laser-particle collider tailored for high-energy photon generation. We show that the use of multiple colliding laser pulses with 0.4 PW of total power is capable of converting more than 18% of the initial multi-GeV electron beam energy into photons, each of which carries more than half of the electron energy.

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30.11.2018
07:08 Arxiv.org PhysicsUltrafast Laser Driven Many-Body Dynamics and Kondo Coherence Collapse. (arXiv:1811.12334v1 [cond-mat.str-el])

Intense ultrafast laser-pulse driven solids have provided systematic insight into the dynamics of electrons in condensed matter systems, which opens up prospects for quantum control of solids and all-optical band structure reconstruction. However, the underlying many-body dynamics in strongly correlated or coupled systems, remains to be understood. Here we consider an ultrafast laser driven Kondo lattice model, in which conduction electrons are strongly coupled with magnetically local moments. The ultrafast laser field excites collective doublon-hole pairs and induces a transient melting of Kondo coherence phase, which is evidenced by the high-frequency photon emission. The theoretical insight is accessible with time- and angle-resolved photoemission spectroscopy and high-harmonic generation spectroscopy, and will stimulate the investigation of non-equilibrium dynamics and nonlinear

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07:08 Arxiv.org PhysicsMicromachining of PMN-PT Crystals with Ultrashort Laser Pulses. (arXiv:1811.12287v1 [physics.app-ph])

Lead-magnesium niobate lead-titanate (PMN-PT) has been proven as an excellent material for sensing and actuating applications. The fabrication of advanced ultra-small PMN-PT-based devices relies on the availability of sophisticated procedures for the micro-machining of PMN-PT thin films or bulk substrates. Approaches reported up to date include chemical etching, excimer laser ablation and ion milling. To ensure an excellent device performance, a key mandatory feature for a micro-machining process is to preserve as far as possible the crystalline quality of the substrates; in other words, the fabrication method must induce a low density of cracks and other kind of defects. In this work, we demonstrate a relatively fast procedure for the fabrication of high-quality PMN-PT micro-machined actuators employing green femtosecond laser pulses. The fabricated devices feature absence of extended cracks

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29.11.2018
09:42 Arxiv.org PhysicsOptimized single-shot laser ablation of concave mirror templates on optical fibers. (arXiv:1811.11532v1 [physics.optics])

We realize mirror templates on the tips of optical fibers using a single-shot CO$_2$ laser ablation procedure. We perform a systematic study of the influence of the pulse power, pulse duration, and laser spot size on the radius of curvature, depth, and diameter of the mirror templates. We find that these geometrical characteristics can be tuned to a larger extent than has been previously reported, and notably observe that compound convex-concave shapes can be obtained. This detailed investigation should help further the understanding of the physics of CO$_2$ laser ablation processes and help improve current models. We additionally identify regimes of ablation parameters that lead to mirror templates with favorable geometries for use in cavity quantum electrodynamics and optomechanics.

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28.11.2018
13:50 Nanowerk.comOptics and laser components out of the 3D-printer

Complete laser systems out of the 3D printer? What sounds like a long way off is the goal of a new research project.

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27.11.2018
08:01 Arxiv.org PhysicsCompact laser system for a laser-cooled ytterbium ion microwave frequency standard. (arXiv:1811.10451v1 [physics.atom-ph])

The development of a transportable microwave frequency standard based on the ground-state transition of $^{171}\mathrm{Yb^{+}}$ at ~12.6 GHz requires a compact laser system for cooling the ions, clearing out of long-lived states and also for photoionisation. In this paper, we describe the development of a suitable compact laser system based on a 6U height rack-mounted arrangement with overall dimensions $260 \times 194 \times 335$ mm. Laser outputs at 369 nm (for cooling), 399 nm (photoionisation), 935 nm (repumping) and 760 nm (state clearout) are combined in a fiber arrangement for delivery to our linear ion trap and we demonstrate this system by cooling of $^{171}\mathrm{Yb^{+}}$ ions. Additionally, we demonstrate that the lasers at 935 nm and 760 nm are close in frequency to water vapor and oxygen absorption lines respectively; specifically, at 760 nm, we show that one

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08:01 Arxiv.org PhysicsHigh contrast linking 6 lasers to a 1 GHz Ybfiber laser frequency comb. (arXiv:1811.09942v1 [physics.optics])

We demonstrate a 0.95 GHz repetition rate fully stabilized Yb:fiber frequency comb without optical amplification. Benefitted from the high mode power and high coherence, this comb achieved 35 dB to 42 dB signal to noise ratio on the direct heterodyne beat signals with at least 6 continuous wave lasers (at 580nm, 679nm, 698nm, 707nm, 813nm and 922 nm) while keeping >40 dB carrier envelop frequency signal. It can be used for the direct measurement of optical frequencies in visible and near-infrared wavelengths, and has a great potential on simultaneous comparison of multiple optical frequencies.

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08:01 Arxiv.org PhysicsFrequency-Stabilized Deep-UV Laser at 243.1 nm with 1.4 W output power. (arXiv:1811.09874v1 [physics.atom-ph])

We demonstrate a 1.4 W continuous wavelength (CW) laser at 243.1 nm. The radiation is generated through frequency quadrupling the output of a ytterbium-doped fiber amplifier system which produces $>$ 10 W of CW power at 972.5 nm. We demonstrate absolute frequency control by locking the laser to an optical frequency comb and exciting the 1S-2S transition in atomic hydrogen. This frequency-stabilized, high-power deep-UV laser should be of significant interest for precision spectroscopy of simple and exotic atoms, two-photon laser cooling of hydrogen, and Raman spectroscopy.

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