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19.07.2019
18:53 Phys.orgX-ray laser sight reveals drug targets

Researchers from the Moscow Institute of Physics and Technology have published a review on serial femtosecond crystallography, one of the most promising methods for analyzing the tertiary structure of proteins. This technique has rapidly evolved over the past decade, opening new prospects for the rational design of drugs targeting proteins previously inaccessible to structural analysis. The article came out in the journal Expert Opinion on Drug Discovery.

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11:25 GizmagPowerful new telescope joins the search for possible laser pulses from aliens


Statistically, it's pretty much a given that alien life is out there somewhere, whether that's Martian microbes or highly intelligent life beaming comms through the cosmos. While the Curiosity rover is poking around in the dirt for the former, the Breakthrough Listen initiative is searching for the latter. Now, a new telescope array has joined the hunt, scanning the skies for flashes of laser light that alien civilizations might be giving off.
.. Continue Reading Powerful new telescope joins the search for possible laser pulses from aliens Category: Space Tags: Astronomy Extraterrestrial Laser Life Light Radio UC Santa Cruz

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03:42 Arxiv.org PhysicsScalable terahertz generation by large-area optical rectification at 80 TW laser power. (arXiv:1907.07704v1 [physics.optics])

We demonstrate high-energy terahertz generation from a large-aperture (75 mm diameter) lithium niobate wafer by using a femtosecond laser with energy up to 2 J. This scheme utilizes optical rectification in a bulk lithium niobate crystal, where most terahertz energy is emitted from a thin layer of the rear surface. Despite its simple setup, this scheme can yield 0.19 mJ of terahertz energy with laser-to-terahertz conversion efficiencies of ~0.01%, about 3 times better than ZnTe when pumped at 800 nm. The experimental setup is up-scalable for multi-mJ terahertz generation with petawatt laser pumping.

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18.07.2019
21:28 ScienceMag.orgLaser holograms stimulate brain cells in mice to probe roots of perception and hallucination

Triggering a handful of neurons may be enough to conjure a visual experience

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06:17 Arxiv.org PhysicsMoulding Wetting by Laser-Induced Nanostructures. (arXiv:1907.07448v1 [physics.app-ph])

In this account, we have exposed multilayer thin metal film samples (each layer of 17 nm thickness) of different materials to femtosecond laser beam at 1030 nm wavelength. The interaction generated high-quality laser-induced periodic surface structures (LIPSS) of spatial period between 740 and 790 nm and with maximal average corrugation height below 100 nm. The contact angle (CA) values of the water droplets on the surface were estimated and the values between unmodified and modified samples were compared. Even though the laser interaction changed both the surface morphology and the chemical composition, the wetting properties were predominantly influenced by the small change in morphology causing the increase of the contact angle for 20% which could not be explained classically. The influence of both surface corrugation and chemical composition to the wetting properties has been thoroughly

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06:17 Arxiv.org PhysicsNonlinear coherence effects in transient-absorption ion spectroscopy with stochastic extreme-ultraviolet free-electron laser pulses. (arXiv:1907.07182v1 [physics.atom-ph])

We demonstrate time-resolved nonlinear extreme-ultraviolet absorption spectroscopy on multiply charged ions, here applied to the doubly charged neon ion, driven by a phase-locked sequence of two intense free-electron laser pulses. Absorption signatures of resonance lines due to 2$p$--3$d$ bound--bound transitions between the spin-orbit multiplets $^3$P$_{0,1,2}$ and $^3$D$_{1,2,3}$ of the transiently produced doubly charged Ne$^{2+}$ ion are revealed, with time-dependent spectral changes over a time-delay range of $(2.4\pm0.3)\,\text{fs}$. Furthermore, we observe 10-meV-scale spectral shifts of these resonances owing to the AC Stark effect. We use a time-dependent quantum model to explain the observations by an enhanced coupling of the ionic quantum states with the partially coherent free-electron-laser radiation when the phase-locked pump and probe pulses precisely overlap in

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17.07.2019
23:08 Medscape.ComFDA Clears Low-Level Laser Device for 'Whole Body' Pain

The FDA has granted marketing clearance for a low-level laser device for the treatment of "whole body" musculoskeletal pain, the manufacturer has announced.

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08:58 Arxiv.org PhysicsRamsey-Bord\'e matter-wave interferometry for laser frequency stabilization at $10^{-16}$ frequency instability and below. (arXiv:1907.06774v1 [physics.atom-ph])

We demonstrate Ramsey-Bord\'e (RB) atom interferometry for high performance laser stabilization with fractional frequency instability $<2 \times 10^{-16}$ for timescales between 10 and 1000s. The RB spectroscopy laser interrogates two counterpropagating $^{40}$Ca beams on the $^1$S$_0$ -- $^3$P$_1$ transition at 657 nm, yielding 1.6 kHz linewidth interference fringes. Fluorescence detection of the excited state population is performed on the (4s4p) $^3$P$_1$ -- (4p$^2$) $^3$P$_0$ transition at 431 nm. Minimal thermal shielding and no vibration isolation are used. These stability results surpass performance from other thermal atomic or molecular systems by one to two orders of magnitude, and further improvements look feasible.

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16.07.2019
21:48 MedicalNewsToday.comMedical News Today: What to know about laser treatment for scars

Laser treatment can help reduce the appearance, pain, and itching of scar tissue. In this article, learn about the procedure of laser treatment and the risks and considerations.

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04:31 Arxiv.org PhysicsPlasma formation and relaxation dynamics in fused silica driven by femtosecond short-wavelength infrared laser pulses. (arXiv:1907.05925v1 [physics.optics])

Laser-induced plasma formation and subsequent relaxation in solid dielectrics is the precursor to structural modifications that are accompanied by a permanent alteration of material properties. The decay of the electron-hole plasma through distinct relaxation channels determines the properties of the resulting modification. Based on an experimental arrangement combining a time-resolved transmission measurement with a cross-phase modulation measurement, we isolate the plasma formation and relaxation dynamics in the bulk of amorphous fused silica excited by femtosecond short-wavelength infrared ($\lambda =\,2100\,$nm) laser pulses. Whereas the relaxation time of the generated electron-hole plasma was so far assumed to be constant, our findings indicate an intensity-dependent relaxation time. We attribute this intensity dependence to vibrational detrapping of self-trapped excitons.

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15.07.2019
07:14 Arxiv.org PhysicsElectron dynamics in counter-propagating laser waves. (arXiv:1907.05539v1 [physics.plasm-ph])

The electron dynamics in counter-propagating laser waves is investigated by employing a novel approach, where the new Hamiltonian is time-independent when the perturbative laser wave is absent. The physical picture of stochastic electron dynamics is clearly revealed and the threshold values of the amplitude of the perturbative laser field for triggering stochastic electron acceleration are derived for different laser polarization directions and initial electron momentum. It demonstrates that the dephasing rate (new Hamiltonian) between the electron and the dominant laser can be randomly reduced if the amplitude of the perturbative laser is above the threshold such that the electron could be accelerated by the dominant laser well beyond the ponderomotive energy scaling. The impact of a superluminal phase velocity is examined, which slightly changes the stochastic region in Hamiltonian space if

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14.07.2019
15:01 GizmagNASA green lights upgrade of Apollo era lunar laser experiment


One of the original designers of a pioneering Apollo Moon experiment is leading an effort to create an upgraded version for future lunar landing missions. A team under professor emeritus at the University of Maryland (UMD), Doug Currie are developing a more accurate version of the Lunar Laser Ranging experiment that was left behind by Apollo 11, 14, and 15 between 1969 and 1971 that allows scientists to measure the distance from the Earth to the Moon extreme accuracy.
.. Continue Reading NASA green lights upgrade of Apollo era lunar laser experiment Category: Space Tags: Apollo 11 Laser Moon University of Maryland

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12.07.2019
19:16 GizmagReview: LaserCube, the world s smallest – and first – battery-powered RGB laser projector


Wicked Lasers' latest gadget is one of the most mesmerizing and compelling toys we've played with in a long, long time. It's also extremely dangerous, powerful enough to pop balloons, etch patterns on wood, and surely fry the odd retina if used incorrectly.
.. Continue Reading Review: LaserCube, the world's smallest – and first – battery-powered RGB laser projector Category: Home Entertainment Tags: Laser Wicked Lasers

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14:25 Technology.orgPhysics of laser frequency combs sheds light on nature’s problem-solving skills

Nature has a way of finding optimal solutions to complex problems. For example, despite billions of ways for

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08:26 Arxiv.org PhysicsInterferometric optical signature of electron microbunching in laser-driven plasma accelerators. (arXiv:1907.05078v1 [physics.acc-ph])

We report observations of coherent optical transition radiation interferometry (COTRI) patterns generated by microbunched ~200-MeV electrons as they emerge from a laser-plasma accelerator. The divergence of the microbunched portion of electrons, deduced by comparison to an analytical COTRI model, is ~6x smaller than the ~3 mrad ensemble beam divergence, while the radius of the microbunched beam, obtained from COTR images on the same shot, is < 3 microns. The combined results show that the microbunched distribution has estimated transverse normalized emittance ~0.5 mm mrad.

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00:29 GizmagLaser tech is set to measure earthquake damage to buildings


How safe would you feel, going back into a multi-story building that had just been through an earthquake? A new sensor system could allay your fears, as it optically measures how much a building has swayed, and thus how damaged it may be.
.. Continue Reading Laser tech is set to measure earthquake damage to buildings Category: Science Tags: Earthquake Laser Lawrence Berkeley National Laboratory Lawrence Livermore National Laboratory University of Nevada

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11.07.2019
17:06 SingularityHub.ComThe Pentagon’s New Laser-Based Tool Uses Your Heartbeat to Track You

The government’s hefty arsenal of surveillance tools just welcomed a powerful new member. Rather than monitoring an external device—a bug or a smartphone—or even the exterior features of your face, the new tech aims straight for your heart. Literally. First reported by MIT Technology Review, the US Pentagon is developing an infrared laser that captures […]

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04:16 Arxiv.org PhysicsZero-velocity atom interferometry using a retroreflected frequency chirped laser. (arXiv:1907.04403v1 [physics.atom-ph])

Atom interferometry using stimulated Raman transitions in a retroreflected configuration is the first choice in high precision measurements because it provides low phase noise, high quality Raman wavefront and simple experimental setup. However, it cannot be used for atoms at zero velocity because two pairs of Raman lasers are simultaneously resonant. Here we report a method which allows to lift this degeneracy by using a frequency chirp on the Raman lasers. Using this technique, we realize a Mach-Zehnder atom interferometer hybridized with a force balanced accelerometer which provides horizontal acceleration measurements with a short-term sensitivity of $3.2\times 10^{-5}$ m.s$^{-2}$/$\sqrt{Hz}$. We check at the level of precision of our experiment the absence of bias induced by this method. This technique could be used for multiaxis inertial sensors, tiltmeters or atom interferometry in a

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10.07.2019
23:16 ScienceDaily.comCould vacuum physics be revealed by laser-driven microbubble?

Scientists have discovered a novel mechanism which they refer to as microbubble implosion (MBI) in 2018. In this study, the group confirmed that during MBI, an ultrahigh electrostatic field close to the Schwinger field could be achieved because micron-sized bubbles embedded in a solid hydride target implode to have nanometer-sized diameters upon ionization.

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07:07 Arxiv.org PhysicsMulti-beam-energy operation for the continuous-wave x-ray free electron laser. (arXiv:1907.04176v1 [physics.acc-ph])

The parallel operation of multiple undulator lines with a wide spectral range is an important way to increase the efficiency of x-ray free electron laser (XFEL) facilities, especially for machines with high-repetition-rate. In this paper, a delay system based on four double bend achromats is proposed to delay electron beams, thereby changing the arrival time of those delayed electron beams in the accelerating structure behind the system. Combined with kickers, the delay system can be used to generate bunch-to-bunch energy changed electron beams in a continuous wave XFEL facility. Start-to-end simulations based on the Shanghai high-repetition-rate XFEL and extreme light facility parameters are performed to demonstrate that the delay system can flexibly control electron beam energy from 1.48 to 8.74 GeV at the end of the linac.

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07:07 Arxiv.org PhysicsSeed and vacuum pair production in strong laser field. (arXiv:1907.03786v1 [physics.atom-ph])

Researches on the electron-positron pair production in the presence of the intense laser field are reviewed, motivated by the theoretical importance of the nonperturbative QED problem and the worldwide development of the strong laser facilities. According to distinct experimental requirements and theoretical methods, two types of pair production are elaborated, which are respectively the pair production in the combination of a seed particle and the strong laser, and vacuum pair production without a seed particle. The origin of the nonperturbative problem caused by the strong field is analyzed. The main idea, realization, achievements, validity, challenges and bottleneck problems of the nonperturbative methods developed for each type of the pair production problem are discussed.

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05:24 GizmagUK expands laser and radio frequency directed energy weapons program


The UK's Ministry of Defence has ordered three laser and radio-frequency weapons demonstrators for the country's Armed Forces. Today's announcement promises £130 million (US$162 million) to test and evaluate the next generation of Directed Energy Weapons (DEWs) with field trials expected to begin in 2023 on Royal Navy ships and British Army vehicles.
.. Continue Reading UK expands laser and radio frequency directed energy weapons program Category: Military Tags: British Army Laser weapon Royal Navy U.K. Ministry of Defence

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09.07.2019
21:13 GizmagLaser "pinging" shows promise for fast and cheap water testing


Looking for impurities in drinking water or other liquids typically involves chemical analysis, which may be time-consuming. Now, however, scientists have created an inexpensive system in which light – that's converted to sound – is used to instantly determine if water is safe to drink.
.. Continue Reading Laser "pinging" shows promise for fast and cheap water testing Category: Science Tags: Laser Photoacoustics University of Missouri Water

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17:02 Phys.orgCould vacuum physics be revealed by laser-driven microbubbles?

A vacuum is generally thought to be nothing but empty space. But in fact, a vacuum is filled with virtual particle-antiparticle pairs of electrons and positrons that are continuously created and annihilated in unimaginably short time-scales.

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16:39 Phys.orgMEMS-in-the-lens architecture for laser scanning microscopy

Laser-scanning microscopes can be miniaturized to image microenvironments in vivo via inclusion inside optical micromechanical system (MEMS) devices to replace the existing larger components. Multifunctional active optical devices are emerging components that support miniaturization for diffraction-limited performance with simpler optical system designs in optical devices. In a recent study, Tianbo Liu and a team of researchers in the departments of Electrical and Computer Engineering and Dermatology in the U.S. proposed a catadioptric (allowing both light reflection and refraction) microscope objective lens, featuring an integrated MEMS device to perform biaxial scanning, axial focus adjustment and control spherical aberration.

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09:57 Arxiv.org PhysicsLaser-driven generation of collimated quasi-monoenergetic proton beam using double-layer target with interface modulations. (arXiv:1907.03489v1 [physics.plasm-ph])

Usage of double-layer targets consisting of heavy and light material with modulated interface between them provides a way for laser-driven generation of collimated ion beams. With extensive 2D3V PIC simulations we show that this configuration may result in a development of a relativistic instability with Rayleigh-Taylor and Richtmyer-Meshkov like features. Initially small perturbations are amplified during the laser-target interaction leading to the formation of low-density plasma regions and high-density bunches between them, which are accelerated by the laser radiation pressure as whole compact structures. That results in collimated quasi-monoenergetic proton beam with high average energy. The properties of this proton beam such as its low emittance (one order of magnitude lower compared to that of conventional accelerators) and divergence are discussed. Results are compared with similar

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09:57 Arxiv.org PhysicsVisualizing the melting processes in ultrashort intense laser triggered gold mesh with high energy electron radiography. (arXiv:1907.03059v1 [physics.app-ph])

High energy electron radiography (HEER) is a promising tool for high energy density physics diagnostics, apart from other tools like X/{\gamma} ray shadowgraphy and high energy proton radiography. Impressive progresses have been made in development and application of HEER in past few years, and proved its potentials for high-resolution imaging of static opaque objects. By taking advantages of short pulse duration and tunable time structure of high energy electron probes, time-resolved imaging measurement of high energy density gold irradiated by ultrashort intense lasers has been performed. Phenomena of different time periods from picosecond to microsecond have been observed, thus proving feasibilities of this technique for imaging of static and dynamic objects.

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09:57 Arxiv.org PhysicsResonant random laser emission from graphene quantum dot doped dye solutions. (arXiv:1907.03003v1 [physics.optics])

Graphene quantum dots (GQDs) are more promising than other kinds of semiconductor QDs because of their photostability and biocompatibility in different applications such as bioimaging, biosensing and light emitting diodes (LEDs). In addition, advances in random lasers (RLs) have led to an emerging desire for developing remote sensing and detecting strategies, lightning and imaging systems that are far cheaper, more precise and simpler. Although combining GQDs and RLs seems promising for the development of advanced biosensing and bioimaging systems, the RLs fabricated based on GQDs have been rarely studied. Here, we report on the fabrication of dye doped GQDs RLs with resonant feedback that are pumped optically with nanosecond pulses. GQDs, synthesized by the pyrolysis of citric acid, are used as scattering centers in an ethylene glycol solution of rhodamine B dye. It is demonstrated

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08.07.2019
05:40 Arxiv.org PhysicsThe effect of hyperfine splitting on Stark broadening for three blue-green Cu I lines in laser-induced plasma. (arXiv:1907.02920v1 [astro-ph.SR])

Stark effect is observed in many natural and artificial plasmas and is of great importance for diagnostic purposes. Since this effect alters profiles of spectral lines, it should be taken into account when assessing chemical composition of radiation sources, including stars. Copper is one of the elements which studies of stellar atmospheres deal with. To this end, UV and visible Cu lines are used. However, there is a lack of agreement between existing data on their Stark parameters. It is therefore of interest to obtain new experimental data on these lines and to compare them to previous results. In this work, we have estimated Stark widths and shifts for three blue-green lines at 5105.54, 5153.24, and 5218.20 A (corresponding transitions are [3d104p] 2P{\deg} - [3d94s2] 2D and [3d104d] 2D - [3d104p] 2P{\deg}) observed in a "long-spark" laser-induced plasma. For the first time, we have

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05:40 Arxiv.org PhysicsResolved Sideband Cooling of a Levitated Nanoparticle in the Presence of Laser Phase Noise. (arXiv:1907.02741v1 [quant-ph])

We investigate the influence of laser phase noise heating on resolved sideband cooling in the context of cooling the center-of-mass motion of a levitated nanoparticle in a high-finesse cavity. Although phase noise heating is not a fundamental physical constraint, the regime where it becomes the main limitation in Levitodynamics has so far been unexplored and hence embodies from this point forward the main obstacle in reaching the motional ground state of levitated mesoscopic objects with resolved sideband cooling. We reach minimal center-of-mass temperatures comparable to $T_{min}=10$mK at a pressure of $p = 3\times 10^{-7}$mbar, solely limited by phase noise. Finally we present possible strategies towards motional ground state cooling in the presence of phase noise.

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07.07.2019
16:12 Technology.orgEndurance Lasers starts a new an already 10-th giveaway: A chance to win a 10-watt laser module

Endurance Lasers, specialists in the field of high-power laser cutting and engraving equipment, have just announced their new

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05.07.2019
12:38 TheStar.comA top-billing doctor charged OHIP for doing an eye procedure more times than all other MDs combined. Another billed for 128 laser treatments in one day. The numbers have some medical experts baffled

Chatham ophthalmologist Christopher Anjema has billed the Ontario Health Insurance Plan for treating patients suffering from common eye problems such as cataracts and glaucoma.
He has also charged the province for doing a not-so-common eyelid reconstruction procedure — again and again.
Known as a Tenzel flap, it’s performed when a patient is missing a hunk of flesh from an eyelid, often because cancerous skin had to be removed. The surgeon makes a small, semicircular incision beside the eye to be able to slide some extra tissue over to repair the eyelid.
Anjema, one of Ontario’s top-billing doctors, charged the province between 2011 and 2018 for 3,305 treatments under the fee code associated with the Tenzel flap, according to billing data released by the Ministry of Health and Long-Term Care.
That’s more than all of the other doctors in the province combined, including the

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06:41 Arxiv.org PhysicsLow threshold anti-Stokes Raman laser on-chip. (arXiv:1907.02448v1 [physics.optics])

Raman lasers based on integrated silica whispering gallery mode resonant cavities have enabled numerous applications from telecommunications to biodetection. To overcome the intrinsically low Raman gain value of silica, these devices leverage their ultra-high quality factors (Q), allowing sub-mW stimulated Raman scattering (SRS) lasing thresholds to be achieved. A closely related nonlinear behavior to SRS is stimulated anti-Stokes Raman scattering (SARS). This nonlinear optical process combines the pump photon with the SRS photon to generate an upconverted photon. Therefore, in order to achieve SARS, the efficiency of the SRS process must be high. As a result, achieving SARS in on-chip resonant cavities has been challenging due to the low lasing efficiencies of these devices. In the present work, metal-doped ultra-high Q (Q>107) silica microcavity arrays are fabricated on-chip. The

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06:41 Arxiv.org PhysicsAnalysis of retinal and choroidal images measured by laser Doppler holography. (arXiv:1907.02355v1 [physics.optics])

Laser Doppler holography (LDH) is a full-field imaging technique that was recently used in the human eye to reveal blood flow contrasts in the retinal and choroidal vasculature non-invasively, and with high temporal resolution. We here demonstrate that the ability of LDH to perform quantitative flow measurements with high temporal resolution enables arteriovenous differentiation in the retina and choroid. In the retina, arteries and veins can be differentiated on the basis of their respective power Doppler waveforms. Choroidal arteries and veins can instead be discriminated by computing low and high frequency power Doppler images to reveal low and high blood flow images, respectively.

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06:41 Arxiv.org PhysicsAccurate single-shot measurement technique for the spectral distribution of GeV electron beams from a laser wakefield accelerator. (arXiv:1907.02239v1 [physics.plasm-ph])

We present a technique, based on a dipole magnet spectrometer containing multiple scintillation screens, to accurately characterize the spectral distribution of a GeV electron beam generated by laser wakefield acceleration (LWFA). An optimization algorithm along with a numerical code was developed for trajectory tracing and reconstructing the electron beam angle, divergence, and energy spectrum with a single-shot measurement. The code was validated by comparing the results with the Monte-Carlo simulation of electron beam trajectories. We applied the method to analyze data obtained from laser wakefield acceleration experiments performed using a multi-Petawatt laser to accelerate electron beams to multi-GeV energy. Our technique offers improved accuracy to faithfully characterize electron beams with non-negligible shot-to-shot beam pointing fluctuations, particularly in the state-of-the-art

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06:41 Arxiv.org PhysicsIon dominated mechanism for coupling laser energy to plasma. (arXiv:1907.02105v1 [physics.plasm-ph])

The well-known schemes (e.g. Brunel, resonance, JxB heating etc.,) of laser energy absorption in plasma are mediated through the lighter electron species. In this work a fundamentally new mechanism of laser energy absorption directly through the heavier ion species has been proposed. The mechanism relies on the difference between the ExB drifts of electron and ions in the oscillating electric field of the laser to create charge density perturbations in the presence of a strong external magnetic field. Particle - In - Cell (PIC) simulations using OSIRIS are carried out which provide clear support for this new absorption mechanism at work.

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06:41 Arxiv.org PhysicsTailoring of an Electron-Bunch Current Distribution via Space-to-Time Mapping of a Transversely-Shaped Photoemission-Laser Pulse. (arXiv:1907.02089v1 [physics.acc-ph])

Temporally-shaped electron bunches at ultrafast time scales are foreseen to support an array of applications including the development of small-footprint accelerator-based coherent light sources or as probes for, e.g., ultrafast electron-diffraction. We demonstrate a method where a transversely-segmented electron bunch produced via photoemission from a transversely-patterned laser distribution is transformed into an electron bunch with modulated temporal distribution. In essence, the presented transformation enables the mapping of the transverse laser distribution on a photocathode surface to the temporal coordinate and provides a proof-of-principle experiment of the method proposed in Reference [\href{https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.108.263904}{W. S. Graves, et al. Phys. Rev. Lett. {\bf 108}, 263904 (2012)}] as a path toward the realization of compact coherent X-ray

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04.07.2019
09:23 Arxiv.org PhysicsSecurity analysis of practical continuous-variable quantum key distribution systems under laser seeding attack. (arXiv:1907.01553v1 [quant-ph])

Here, we investigate the security of the practical one-way CVQKD and CV-MDI-QKD systems under laser seeding attack. In particular, Eve can inject a suitable light into the laser diodes of the light source modules in the two kinds of practical CVQKD systems, which results in the increased intensity of the generated optical signal. The parameter estimation under the attack shows that the secret key rates of these two schemes may be overestimated, which opens a security loophole for Eve to successfully perform an intercept-resend attack on these systems. To close this loophole, we propose a real-time monitoring scheme to precisely evaluate the secret key rates of these schemes. The analysis results indicate the implementation of the proposed monitoring scheme can effectively resist this potential attack.

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09:23 Arxiv.org CSIntrinsic Calibration of Depth Cameras for Mobile Robots using a Radial Laser Scanner. (arXiv:1907.01839v1 [cs.RO])

Depth cameras, typically in RGB-D configurations, are common devices in mobile robotic platforms given their appealing features: high frequency and resolution, low price and power requirements, among others. These sensors may come with significant, non-linear errors in the depth measurements that jeopardize robot tasks, like free-space detection, environment reconstruction or visual robot-human interaction. This paper presents a method to calibrate such systematic errors with the help of a second, more precise range sensor, in our case a radial laser scanner. In contrast to what it may seem at first, this does not mean a serious limitation in practice since these two sensors are often mounted jointly in many mobile robotic platforms, as they complement well each other. Moreover, the laser scanner can be used just for the calibration process and get rid of it after that. The main contributions

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03.07.2019
04:50 Arxiv.org PhysicsObliquely Incident Laser and Electron Beam Interaction in an Undulator. (arXiv:1907.01360v1 [physics.acc-ph])

The angular drift of a laser beam is of particular concern in applications such as seeded free-electron lasers. A systematical study of the obliquely incident laser and electron beam interaction in an undulator is presented in this paper. Theoretical analysis and numerical simulations demonstrate that the interaction would imprint energy and angular modulations on the electron beam simultaneously. Compared with the normally incident pattern, the obliquely incident laser-electron interaction leads to reductions in the bunching factors of HGHG and EEHG. In the meanwhile, proactive applications of this multi-dimensional modulation technique may bring vitality to the field of laser-electron manipulation

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04:50 Arxiv.org PhysicsMCF solitons and laser pulse self-compression at light bullet excitation in the central core of MCF. (arXiv:1907.01275v1 [physics.optics])

The propagation of laser pulses in multi-core fibers (MCF) made of a central core and an even number of cores located in a ring around it is studied. Approximate quasi-soliton homogeneous solutions of the wave field in the considered MCF are found. The stability of the in-phase soliton distribution is shown analytically and numerically. At low energies, its wave field is distributed over all MCF cores and has a duration, which exceeds the duration of the NSE soliton with the same energy by many (five-six) times. On the contrary, almost all of the radiation at high energies is concentrated in the central core with a duration similar to the NSE soliton. The transition between the two types of distributions is very sharp and occurs at a critical energy, which is weakly dependent on the number of cores and on the coupling coefficient with the central core. The self-compression mechanism of laser

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00:16 ScienceDaily.comHigh brightness mid-infrared laser expands horizon of spectroscopic analytical technique

Researchers have used an extremely bright mid-infrared laser to perform an analytical technique known as spectroscopic ellipsometry. The new approach captures high-resolution spectral information in less than a second and could offer new insights into quickly changing properties of a variety of samples from plastics to biological materials.

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02.07.2019
20:13 Phys.orgHigh brightness mid-infrared laser expands horizon of spectroscopic analytical technique

Researchers have used an extremely bright mid-infrared laser to perform an analytical technique known as spectroscopic ellipsometry. The new approach captures high-resolution spectral information in less than a second and could offer new insights into quickly changing properties of a variety of samples from plastics to biological materials.

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20:02 Phys.orgThe world's first high-intensity laser pulses shaped like a corkscrew

University of California San Diego researchers have calculations for how to create high-intensity twisted laser beams—a flavor of laser pulse the world has likely never seen. These researchers also have done the math on how to use these corkscrew shaped laser pulses to do cutting-edge research. Finally, they have predictions on how the materials that they plan to "drill" into with corkscrew light pulses will respond.

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19:50 Technology.orgDiode lasers vs. Co2 laser tubes

There is a big dispute going on for the last couple of years what is better – a

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07:39 Arxiv.org PhysicsThe laser-based time calibration system for the MEG II pixelated Timing Counter. (arXiv:1907.00911v1 [physics.ins-det])

We have developed a new laser-based time calibration system for highly segmented scintillator counters like the MEG II pixelated Timing Counter (pTC), consisting of 512-centimeter scale scintillator counters read out by silicon photomultipliers (SiPMs). It is difficult to apply previous laser-based calibration methods for conventional meter-scale Time-Of-Flight detectors to the MEG II pTC from the implementation and the accuracy points of view. This paper presents a new laser-based time calibration system which can overcome such difficulties. A laser pulse is split into each scintillator counter via several optical components so that we can directly measure the time offset of each counter relative to the laser-emitted time. We carefully tested all the components and procedures prior to the actual operation. The laser system was installed into the pTC and thoroughly tested under the real

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07:39 Arxiv.org PhysicsCEP-Controlled Molecular Dissociation by Ultrashort Chirped Laser Pulses. (arXiv:1907.00843v1 [physics.atom-ph])

We demonstrate and characterize that a carrier-envelope-phase (CEP)-controlled ultrashortchirped field is an efficient and robust mechanism to modify the dissociation dynamics of molecularhydrogen. Different dissociation pathways are collectively induced and their interference contributeto the kinetic energy release spectra. Chirping is able to efficiently manipulate the interferencesof different dissociation pathways. We demonstrate a linear relationship between chirp and CEP-dependence, dissociation as well as directional electron localization.

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07:39 Arxiv.org PhysicsMulti-photon regime of non-linear Breit-Wheeler and Compton processes in short linearly and circularly polarized laser pulses. (arXiv:1907.00643v1 [physics.plasm-ph])

Non-linear Breit-Wheeler $e^+e^-$ pair production and its crossing channel - the non-linear Compton process - in the multi-photon regime are analyzed for linearly and circularly polarized short laser pulses. We show that (i) the azimuthal angular distributions of outgoing electrons in these processes differ on a qualitative level, and (ii) they depend on the polarization properties of the pulses. A finite carrier envelope phase (CEP) leads to a non-trivial non-monotonic behavior ofthe azimuthal angle distributions of the considered processes. That effect can be used for the (CEP) determination.

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07:39 Arxiv.org PhysicsPicosecond pulses from a mid-infrared interband cascade laser. (arXiv:1907.00346v1 [physics.app-ph])

The generation of mid-infrared pulses in monolithic and electrically pumped devices is of great interest for mobile spectroscopic instruments. The gain dynamics of interband cascade lasers (ICL) are promising for mode-locked operation at low threshold currents. Here, we present conclusive evidence for the generation of picosecond pulses in ICLs via active mode-locking. At small modulation power, the ICL operates in a linearly chirped frequency comb regime characterized by strong frequency modulation. Upon increasing the modulation amplitude, the chirp decreases until broad pulses are formed. Careful tuning of the modulation frequency minimizes the remaining chirp and leads to the generation of 3.2 ps pulses.

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07:39 Arxiv.org PhysicsOn orbit performance of the GRACE Follow-On Laser Ranging Interferometer. (arXiv:1907.00104v1 [astro-ph.IM])

The Laser Ranging Interferometer (LRI) instrument on the Gravity Recovery and Climate Experiment (GRACE) Follow-On mission has provided the first laser interferometric range measurements between remote spacecraft, separated by approximately 220 km. Autonomous controls that lock the laser frequency to a cavity reference and establish the 5 degree of freedom two-way laser link between remote spacecraft succeeded on the first attempt. Active beam pointing based on differential wavefront sensing compensates spacecraft attitude fluctuations. The LRI has operated continuously without breaks in phase tracking for more than 50 days, and has shown biased range measurements similar to the primary ranging instrument based on microwaves, but with much less noise at a level of $1\,{\rm nm}/\sqrt{\rm Hz}$ at Fourier frequencies above 100 mHz.

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01.07.2019
10:15 Arxiv.org PhysicsSuperdiffusive random laser. (arXiv:1906.12306v1 [physics.optics])

The peculiar characteristics of random laser emission have been studied in many different media, leading to a classification of the working regimes based on the statistics of spectral fluctuations. Alongside such studies, the possibility to constrain light propagation by L\'evy walks, i.e. with a `heavy-tailed' distribution of steps, has opened the opportunity to investigate the behavior of a superdiffusive optical gain medium, that can lead to a "superdiffusive random laser." Here, we present a theoretical investigation, based on Monte Carlo simulations, on such a kind of medium, focusing on the widespread presence of fluctuation regimes, that, in contrast to a diffusive random laser, appears very hard to switch off by changing the gain and scattering strength. Hence, the superdiffusion appears as a condition that increases the value of the threshold energy and promotes the presence of

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10:15 Arxiv.org PhysicsPhonon-laser sensing in a hetero optomechanical crystal cavity. (arXiv:1906.12057v1 [physics.optics])

Micro- and nanomechanical resonators have emerged as promising platforms for sensing a broad range of physical properties such as mass, force, torque, magnetic field, and acceleration. The sensing performance relies critically on the motional mass, the mechanical frequency, and the linewidth of the mechanical resonator. Here, we demonstrate a hetero optomechanical crystal (OMC) cavity based on a silicon nanobeam structure. The cavity supports phonon lasing in a fundamental mechanical mode with a frequency of 5.91 GHz, an effective mass of 116 fg, and a mechanical linewidth narrowing from 3.3 MHz to 5.2 kHz, while the optomechanical coupling rate of is as high as 1.9 MHz. With this phonon laser, the on-chip sensing with a resolution of $\delta$$\lambda$/$\lambda$ = 1.0*10-8 can be attained, which is at least two orders of magnitude larger than that obtained with conventional silicon-based

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10:15 Arxiv.org PhysicsSimultaneous polarization transformation and amplification of multi-petawatt laser pulses in magnetized plasmas. (arXiv:1906.12012v1 [physics.plasm-ph])

With increasing laser peak power, the generation and manipulation of high-power laser pulses becomes a growing challenge for conventional solid-state optics due to their limited damage threshold. As a result, plasma-based optical components which can sustain extremely high fields are attracting increasing interest. Here, we propose a type of plasma waveplate based on magneto-optical birefringence under a transverse magnetic field, which can work under extremely high laser power. Importantly, this waveplate can simultaneously alter the polarization state and boost the peak laser power. It is demonstrated numerically that an initially linearly polarized laser pulse with 5 petawatt peak power can be converted into a circularly polarized pulse with a peak power higher than 10 petawatts by such a waveplate with a centimeter-scale diameter. The energy conversion efficiency of the polarization

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10:15 Arxiv.org PhysicsNon-stochastic electron acceleration in multipicosecond laser-solid interaction at relativistic intensity. (arXiv:1906.11975v1 [physics.plasm-ph])

We study energetic electron generation in the characteristic long underdense ion shelf and opaque plasma wall preplasma profile created by multipicosecond, relativistic intensity laser pulses incident on solid density targets. In 1D particle-in-cell simulations, high energy electrons originate in the plasma wall and follow a single-bounce trajectory consisting of initial backward acceleration along the shelf, bounce in the vacuum past the shelf edge, and strong forward acceleration into the wall. During the final forward propagation stage, electrons are direct laser accelerated to more than 10 times the vacuum ponderomotive energy ($\sim m_e c^2 a_0^2/2$) without slipping substantially in the phase they experience in the incident laser over the full shelf length. With the help of a model for electron acceleration in counter-propagating laser pulses, we find that this final forward

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29.06.2019
16:12 ExtremeTech.comThe Pentagon Developed a Laser That Identifies People by Their Heartbeat

The "Jetson" system uses a laser to measure a person's heartbeat, which is apparently almost as distinctive as other biometric indicators. 
The post The Pentagon Developed a Laser That Identifies People by Their Heartbeat appeared first on ExtremeTech.

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28.06.2019
13:55 Zdnet.comThe Pentagon's laser can recognize you by your heartbeat

Clothes or tin foil hats won’t make a difference.

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04:16 Arxiv.org PhysicsBurst behavior due to quasimode excited by stimulated Brillouin scattering in high-intensity laser-plasma interaction. (arXiv:1906.11616v1 [physics.plasm-ph])

The strong-coupling mode, called quasimode, will be excited by stimulated Brillouin scattering (SBS) in high-intensity laser-plasma interaction. And SBS of quasimode will compete with SBS of fast mode (or slow mode) in multi-ion species plasmas, thus leading to a low-frequency burst behavior of SBS reflectivity. The competition of quasimode and ion-acoustic wave (IAW) is an important saturation mechanism of SBS in high-intensity laser-plasma interaction. These results give a clear explanation to the low-frequency periodic burst behavior of SBS and should be considered as a saturation mechanism of SBS in high-intensity laser-plasma interaction.

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04:16 Arxiv.org PhysicsThe effect of Coulomb field on laser-induced ultrafast imaging methods. (arXiv:1906.11503v1 [physics.atom-ph])

The deconvolution procedure of the laser-induced ultrafast imaging schemes is usually based on strong field approximation (SFA) wherein the Coulomb interaction between the parent ion and the freed electron is ignored after ionization. In the laser-induced electron diffraction (LIED) approach, for example, the high energy part of the above-threshold ionization (ATI) spectrum used for analysis is assumed to be produced mostly by the 1st-return-recollision trajectories according to the SFA. By performing a joint theoretical and experimental investigation on the ATI spectrum, the dominant role of the 3rd-return-recollision trajectories in the high energy part of the spectrum due to the ionic Coulomb field is identified, which invalidates the key assumption adopted in the conventional LIED approach. Since the incident (return) electron beams produced by the 1st and 3rd returns possess distinct

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00:29 ScienceNewsDaily.orgThe Pentagon has a laser that can identify people from a distance—by their heartbeat

The Jetson prototype can pick up on a unique cardiac signature from 200 meters away, even through clothes.

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27.06.2019
12:23 TechnologyReview.comThe Pentagon has a laser that can identify people from a distance—by their heartbeat

The Jetson prototype can pick up on a unique cardiac signature from 200 meters away, even through clothes.

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07:04 Arxiv.org PhysicsInterferometry for full temporal reconstruction of laser-plasma accelerator-based seeded free electron lasers. (arXiv:1906.11140v1 [physics.acc-ph])

The spectacular development of Laser-Plasma Accelerators (LPA) appears very promising for a free electron laser application. The handling of the inherent properties of those LPA beams already allowed controlled production of LPA-based spontaneous undulator radiation. Stepping further, we here unveil that the forthcoming LPA-based seeded FELs will present singular spatio-spectral distributions. Relying on numerical simulations and simple analytical models, we show how those interferometric patterns can be exploited to retrieve, in single-shot, the spectro-temporal content and source point properties of the FEL pulses.

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07:04 Arxiv.org PhysicsPulse shaping by a frequency filtering of a sawtooth phase-modulated CW laser. (arXiv:1906.11091v1 [physics.optics])

The spectrum of a CW field whose phase experiences a periodic sawtooth modulation is analyzed. Two types of the sawtooth phase modulation are considered. One is created by combining many harmonics of the fundamental frequency. The second is produced by electro-optic modulator fed by the relaxation oscillator, which generates a voltage slowly rising during charging the energy storage capacitor and dropping fast due to discharge by a short circuit. It is proposed to filter out the main spectral component of the sawtooth phase modulated field. This filtering produces short pulses from CW phase modulated field. Several filters are proposed to remove the selected spectral component. It is shown that such a filtering is capable to produce a train of short pulses. Duty cycle of this train is equal to the modulation period and duration of the pulses can vary from $10^{-1}$ to $10^{-2}$ of the period.

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26.06.2019
15:54 Phys.orgHigh-powered laser diodes can reduce residual stress in metal 3-D printed parts

In 3-D printing, residual stress can build up in parts during the printing process due to the expansion of heated material and contraction of cold material, generating forces that can distort the part and cause cracks that can weaken or tear a part to pieces, especially in metals.

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14:33 Technology.orgHigh-powered laser diodes can reduce residual stress in metal 3D printed parts

In 3D printing, residual stress can build up in parts during the printing process due to the expansion

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09:43 Arxiv.org PhysicsTunable Isolated Attosecond X-ray Pulses with Gigawatt Peak Power from a Free-Electron Laser. (arXiv:1906.10649v1 [physics.optics])

The quantum mechanical motion of electrons in molecules and solids occurs on the sub-femtosecond timescale. Consequently, the study of ultrafast electronic phenomena requires the generation of laser pulses shorter than 1 fs and of sufficient intensity to interact with their target with high probability. Probing these dynamics with atomic-site specificity requires the extension of sub-femtosecond pulses to the soft X-ray spectral region. Here we report the generation of isolated GW-scale soft X-ray attosecond pulses with an X-ray free-electron laser. Our source has a pulse energy that is six orders of magnitude larger than any other source of isolated attosecond pulses in the soft X-ray spectral region, with a peak power in the tens of gigawatts. This unique combination of high intensity, high photon energy and short pulse duration enables the investigation of electron dynamics with X-ray

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09:43 Arxiv.org PhysicsDirect-drive measurements of laser-imprint-induced shock velocity nonuniformities. (arXiv:1906.10542v1 [physics.plasm-ph])

Perturbations in the velocity profile of a laser-ablation-driven shock wave seeded by speckle in the spatial beam intensity (i.e., laser imprint) have been measured. Direct measurements of these velocity perturbations were recorded using a two-dimensional high-resolution velocimeter probing plastic material shocked by a 100-ps picket laser pulse from the OMEGA laser system. The measured results for experiments with one, two, and five overlapping beams incident on the target clearly demonstrate a reduction in long-wavelength ($>$25 um) perturbations with an increasing number of overlapping laser beams, consistent with theoretical expectations. These experimental measurements are crucial to validate radiation-hydrodynamics simulations of laser imprint for laser direct drive inertial confinement fusion research since they highlight the significant (factor of 3) underestimation of the level of

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09:43 Arxiv.org PhysicsHolographic interferences in strong-field ionization beyond the dipole approximation: The influence of the peak and focal volume averaged laser intensity. (arXiv:1906.10485v1 [physics.atom-ph])

In strong-field ionization interferences between electron trajectories create a variety of interference structures in the final momentum distributions. Among them, the interferences between electron pathways that are driven directly to the detector and the ones that rescatter significantly with the parent ion lead to holography-type interference patterns that received great attention in recent years. In this work, we study the influence of the magnetic field component onto the holographic interference pattern, an effect beyond the electric dipole approximation, in experiment and theory. The experimentally observed nondipole signatures are analyzed via quantum trajectory Monte Carlo simulations. We provide explanations for the experimentally demonstrated asymmetry in the holographic interference pattern and its non-uniform photoelectron energy dependence as well as for the variation of the

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09:43 Arxiv.org PhysicsLaser-Induced Dissociative Recombination of Carbon Dioxide. (arXiv:1906.10429v1 [physics.chem-ph])

We experimentally investigate laser-induced dissociative recombination of CO$_2$ in linearly polarized strong laser fields with coincidence measurements. Our results show laser-induced dissociation processes originate from an electron recombination process after laser-induced double ionization. After double ionization of CO$_2$, one electron is recaptured by the CO$_2^{2+}$ and localized to O$^+$ or CO$^+$ in the following dissociation process. We found that the probability of electron localization to O$^{+}$ is much higher than that to CO$^+$. Further, our measurements reveal that the recombination probability of the first ionized electron is three times as high as that of the second ionized electron. Our work may trigger further experimental and theoretical studies on involved nuclear and electron dynamics in laser-induced dissociative recombination of molecules and their applications in

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09:43 Arxiv.org PhysicsX-ray photon scattering at a focused high-intensity laser pulse. (arXiv:1906.10122v1 [physics.optics])

We study x-ray photon scattering in the head-on collision of an XFEL pulse and a focused high-intensity laser pulse, described as paraxial Laguerre-Gaussian beam of arbitrary mode composition. For adequately chosen relative orientations of the polarization vectors of the colliding laser fields, this gives rise to a vacuum birefringence effect manifesting itself in polarization flipped signal photons. Throughout this article the XFEL is assumed to be mildly focused to a waist larger than that of the high-intensity laser beam. As previously demonstrated for the special case of a fundamental paraxial Gaussian beam, this scenario is generically accompanied by a scattering phenomenon of x-ray energy signal photons outside the forward cone of the XFEL beam, potentially assisting the detection of the effect in experiment. Here, we study the fate of the x-ray scattering signal under exemplary

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09:43 Arxiv.org CSA laser-microfabricated electrohydrodynamic thruster for centimeter-scale aerial robots. (arXiv:1906.10210v1 [cs.RO])

Interest in flying insect-sized robots is driven by their advantages over larger robots. Their small size and low weight allow for larger deployment numbers for greater coverage at the same cost. Flapping wings represent one means for generating lift, but this requires a complex and failure-prone mechanism. A simpler alternative is electrohydrodynamics (EHD) thrust, which requires no moving mechanical parts. An EHD thruster creates a stream of ions through corona discharge at a sharp emitter tip. The ions are accelerated through an electric field, where they transfer their momentum to neutral air molecules through impacts, creating thrust. Previous work reported a 30 mg aircraft able to lift its own weight that was fabricated from predominantly silicon components formed through reactive ion etching. To avoid the expense and time associated with that process, here we introduce an alternative

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25.06.2019
20:29 News-Medical.NetLaser light helps identify tumors

It can take up to four weeks before patients can be sure whether the entire tumor has been removed during cancer surgery.

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18:24 Rejuvenation ResearchWill Repeated Ablative Er:YAG Laser Treatment Sessions Cause Facial Skin Sensitivity? Results of a 12-Month, Prospective, Randomized Split-Face Study

Rejuvenation Research, Ahead of Print.

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05:24 Arxiv.org PhysicsQuantum backreaction in laser-driven plasma. (arXiv:1906.09606v1 [physics.plasm-ph])

We present a new approach for investigating quantum effects in laser-driven plasma. Unlike the modelling strategies underpinning particle-in-cell codes that include the effects of quantum electrodynamics, our new field theory incorporates multi-particle effects from the outset. Our approach is based on the path-integral quantisation of a classical bi-scalar field theory describing the behaviour of a laser pulse propagating through an underdense plasma. Results established in the context of quantum field theory on curved spacetime are used to derive a non-linear, non-local, effective field theory that describes the evolution of the laser-driven plasma due to quantum fluctuations. As the first application of our new theory, we explore the behaviour of perturbations to fields describing a uniform, monochromatic, laser beam propagating through a uniform plasma. Our results suggest that quantum

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05:24 Arxiv.org PhysicsLaser-plasma accelerated protons: energy increase in gas-mixtures using high mass number atomic species. (arXiv:1906.09517v1 [physics.plasm-ph])

The idea of using a gas-mixture comprising atoms with high mass number in order to increase proton energies in laser induced plasma acceleration at under critical density is investigated by means of 2D PIC (Particle-In-Cell) simulations. Comparing and discussing the case of a pure hydrogen plasma, and that of a plasma containing higher mass number species with a small percentage of hydrogen, we demonstrated that the mixture enhances the energies of the accelerated protons. We also show that using a gas-mixture introduces the possibility of using the densities ratio to change the relative acceleration of the species.

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05:24 Arxiv.org PhysicsOutput coupling from x-ray free-electron laser cavities with intracavity beam splitters. (arXiv:1906.09509v1 [physics.acc-ph])

Permeable mirrors are typically used for coupling photons out of laser cavities. A similar approach was proposed for output coupling photons from the cavities of x-ray free-electron laser (XFEL) oscillators. One of the Bragg-reflecting crystal mirrors is thin, just a few extinction length, and is used as a permeable mirror. However, this method is very often limited to extractions of only a few tenths of the intracavity power. Other cavity-based XFELs, such as the high-gain regenerative amplifier XFEL, require much higher outcoupling efficiency. Here, alternative schemes are proposed and analyzed for coupling x-ray photons out of XFEL cavities using intracavity Bragg-reflecting, x-ray-transparent diamond crystal beam splitters. The intracavity beam splitters are efficient and flexible in terms of the amount of the power they are capable of coupling out of the cavity, an amount that can be

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24.06.2019
08:04 Arxiv.org PhysicsDirect micro-structuring of Si(111) surfaces through nanosecond-laser Bessel beams. (arXiv:1906.09193v1 [physics.app-ph])

We present here a nanosecond laser ablation of Si(111) wafer with diffraction-free (Bessel-$J_0$) beams. First, the Axicon a conical shaped optical element for beam shaping is characterized with a visible and infrared light sources. Then, ablation profiles are obtained with Bessel beams generated for $\alpha=1^{\circ}$ and $\alpha=20^{\circ}$ base angles, then they are characterized via a Scanning Electron, an Atomic Force and an Optical Interferometric Microscopes. Experimental results compared with theoretical predictions obtained by using Bessel functions. Results show that Bessel beams give possibility of straightforward micro-structuring of Si(111) samples because the only central spot of Bessel beams could damage the surface provided that the laser pulse energy becomes in energy-range we found in our experiments. Moreover, our results clearly indicate that reduced HAZ area due to

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21.06.2019
08:48 Arxiv.org PhysicsOptomechanical response with nanometer resolution in the self-mixing signal of a terahertz quantum cascade laser. (arXiv:1906.08588v1 [physics.optics])

The effectiveness of self-mixing interferometry has been demonstrated across the electromagnetic spectrum, from visible to microwave frequencies, in a plethora of sensing applications, ranging from distance measurement to material analysis, microscopy and coherent imaging. Owing to their intrinsic stability to optical feedback, quantum cascade lasers (QCLs) represent a source that offers unique and versatile characteristics to further improve the self-mixing functionality at mid infrared and terahertz (THz) frequencies. Here, we show the feasibility of detecting with nanometer precision deeply subwalength (< {\lambda}/6000) mechanical vibrations of a suspended Si3N4-membrane used as the external element of a THz QCL feedback interferometric apparatus. Besides representing a platform for the characterization of small displacements, our self-mixing configuration can be exploited for the

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08:48 Arxiv.org PhysicsAb-initio calculations of laser-atom interactions reveal harmonics feedback during macroscopic propagation. (arXiv:1906.08480v1 [physics.optics])

We couple the full 3D ab initio quantum evolution of the light pulse polarization in interaction with an atom with a propagation model to simulate the propagation of ultrashort laser pulses over macroscopic dimensions, in the presence of self-generated harmonics up to order 11. We evidence a clear feedback of the generated harmonics on propagation, with an influence on the ionization probability as well as the yield of the harmonic generation itself.

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08:48 Arxiv.org PhysicsThe laser calibration system of the Muon $g-2$ experiment at Fermilab. (arXiv:1906.08432v1 [physics.ins-det])

The Muon $g-2$ experiment, E989, is currently taking data at Fermilab with the aim to improve the experimental error on the muon anomaly by a factor of four and possibly clarify the current discrepancy with the theoretical prediction. A central component of this four-fold improvement in precision is the laser calibration system of the calorimeters, which has to monitor the gain variations of the photo-sensors with a 0.04% precision on the short-term ($\sim 1\,$ms). This is about one order of magnitude better than what has ever been realized for the calibration of a particle physics calorimeter. The system is designed to monitor also long-term gain variations, mostly due to temperature effects, with a precision below the per mille level. This article reviews the design, the implementation and the performances of the Muon $g-2$ laser calibration system, showing how the experimental requirements

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08:48 Arxiv.org PhysicsDelayed-rate equations model for femtosecond laser-induced breakdown in dielectrics. (arXiv:1906.08338v1 [physics.comp-ph])

Experimental and theoretical studies of laser-induced breakdown in dielectrics provide conflicting conclusions about the possibility to trigger ionization avalanche on the sub-picosecond time scale and the relative importance of carrier-impact ionization over field ionization. On the one hand, current models based on single ionization-rate equations do not account for the gradual heating of the charge carriers which, for short laser pulses, might not be sufficient to start an avalanche. On the other hand, models based on multiple rate equations that track the carriers kinetics rely on several free parameters, which limits the physical insight that we can gain from them. In this paper, we develop a model that overcomes these issues by tracking both the plasma density and carriers' mean kinetic energy as a function of time, forming a set of delayed rate equations that we use to match the

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08:48 Arxiv.org PhysicsTransverse forces in planar symmetric dielectric laser-driven accelerators. (arXiv:1906.08316v1 [physics.acc-ph])

The use of dielectric microstructures driven by solid state lasers to accelerate charged particles or to transversely deflect them is a growing area of scientific interest with an international collaboration of researchers working to develop this concept. Many experimental efforts and new designs use a planar symmetric geometry with sub-micron apertures for the particle beam. We provide a general theoretical framework for the electromagnetic fields in this type of geometry, including derivation of the TE and TM modes supported, and examine the transverse force components exerted on the beam, which may be used for focusing or for deflection of the particles.

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20.06.2019
18:14 ScienceDaily.comLaser method promising for detecting trace chemicals in air

Researchers have developed a new laser-based method that can detect electric charges and chemicals of interest with unprecedented sensitivity. The new approach could one day offer a way to scan large areas for radioactive material or hazardous chemicals for safety and security applications.

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17:09 Phys.orgLaser method promising for detecting trace chemicals in air

Researchers have developed a new laser-based method that can detect electric charges and chemicals of interest with unprecedented sensitivity. The new approach could one day offer a way to scan large areas for radioactive material or hazardous chemicals for safety and security applications.

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15:07 News-Medical.NetCytek Biosciences unveils advanced five-laser flow cytometer

When five lasers and more than 30 colors combine, new breakthroughs and scientific discoveries take shape.

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14:57 Phys.orgResearchers improve semiconductor laser on silicon

Electrical engineering researchers have boosted the operating temperature of a promising new semiconductor laser on silicon substrate, moving it one step closer to possible commercial application.

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10:31 Arxiv.org CSAutomatic Scale Estimation of Structure from Motion based 3D Models using Laser Scalers. (arXiv:1906.08019v1 [cs.CV])

Recent advances in structure-from-motion techniques are enabling many scientific fields to benefit from the routine creation of detailed 3D models. However, for a large number of applications, only a single camera is available, due to cost or space constraints in the survey platforms. Monocular structure-from-motion raises the issue of properly estimating the scale of the 3D models, in order to later use those models for metrology. The scale can be determined from the presence of visible objects of known dimensions, or from information on the magnitude of the camera motion provided by other sensors, such as GPS.
This paper addresses the problem of accurately scaling 3D models created from monocular cameras in GPS-denied environments, such as in underwater applications. Motivated by the common availability of underwater laser scalers, we present two novel approaches. A fully-calibrated

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05:28 News-Medical.NetNew laser treatment aims to stop the development of age-related vision loss

There are 200 million people in the world living with AMD, and in approximately a fifth of these cases, the disease progresses to an advanced stage, leading to visual impairment.

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04:22 Arxiv.org PhysicsTable-top high-energy 7 um OPCPA and 260 mJ Ho:YLF pump laser. (arXiv:1906.08163v1 [physics.optics])

We present the state of the art of a compact high-energy mid-infrared laser system for TW-level 8-cycle pulses at 7 um. This system consists of an Er:Tm:Ho:fiber MOPA which serves as the seeder for a ZGP-based OPCPA chain in addition to a Ho:YLF amplifier which is Tm:fiber pumped. Featuring all-optical synchronization, the system delivers 260-mJ pump energy at 2052 nm, 16-ps duration at 100 Hz with a stability of 0.8 % rms over 20 min. We show that chirp inversion in the OPCPA chain leads to excellent energy extraction and aids in compression of the 7-um pulses to 8 optical cycles (188 fs) in bulk BaF2 with 93.5 % efficiency. Using 21.7 mJ of the available pump energy, we generate 0.75-mJ-energy pulses at 7 um due to increased efficiency with a chirp-inversion scheme. The pulse quality of the system's output is shown by generating high harmonics in ZnSe which span up to harmonic order 13 with

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04:22 Arxiv.org PhysicsQuantum dynamics of atomic Rydberg excitation in strong laser fields. (arXiv:1906.08093v1 [physics.atom-ph])

Neutral atoms have been observed to survive intense laser pulses in high Rydberg states with surprisingly large probability. Only with this Rydberg-state excitation (RSE) included is the picture of intense-laser-atom interaction complete. Various mechanisms have been proposed to explain the underlying physics. However, neither one can explain all the features observed in experiments and in time-dependent Schr\"{o}dinger equation (TDSE) simulations. Here we propose a fully quantum-mechanical model based on the strong-field approximation (SFA). It well reproduces the intensity dependence of RSE obtained by the TDSE, which exhibits a series of modulated peaks. They are due to recapture of the liberated electron and the fact that the pertinent probability strongly depends on the position and the parity of the Rydberg state. We also present measurements of RSE in xenon at 800 nm, which display the

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04:22 Arxiv.org PhysicsThermal emittance mapping of a cesium telluride photocathode using microlens-arrays based laser pattern beam. (arXiv:1906.08074v1 [physics.acc-ph])

The thermal emittance map of the cesium telluride photocathode is measured using a laser pattern beam produced by microlens arrays. A pair of MLAs are employed to produce a periodic transverse pattern beam, consisting of a two-dimensional array of laser beamlets. The laser pattern beam was illuminated onto the cesium telluride cathode to produce an electron pattern beam. The rms beamsize of the electron beamlets is monitored on a YAG screen with different solenoid strengths, and the thermal emittance is fitted by the solenoid scan method. The measured thermal emittances of seven beamlets vary from 0.934 mm mrad/mm to 1.142 mm mrad/mm. The thermal emittance of each beamlet is compared with the quantum efficiency, demonstrating the dependence of the thermal emittance on the quantum efficiency for the cesium telluride photocathode.

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04:22 Arxiv.org PhysicsUp to 70 THz bandwidth from implanted Ge photoconductive antenna excited by a fibre laser. (arXiv:1906.08028v1 [physics.optics])

Phase-stable electromagnetic pulses in the THz frequency range offer several unique capabilities in time-resolved spectroscopy. However, the diversity of their application is limited by the covered spectral bandwidth. In particular, the upper frequency limit of photoconductive emitters - the most widespread technique in THz spectroscopy - reaches only up to 7 THz in regular transmission mode due to the absorption by infrared-active optical phonons. Here, we present ultra-broadband (extending up to 70 THz) THz emission from Au implanted Ge emitter which is compatible with a fibre laser operating at 1.2 and 1.55 {\mu}m wavelengths at a repetition rates of 10 and 20 MHz, respectively. This opens a perspective for the development of compact THz photonic devices operating up to multi-THz frequencies and compatible with Si CMOS technology.

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19.06.2019
07:07 Arxiv.org PhysicsMegahertz X-ray microscopy at X-ray Free-Electron Laser and Synchrotron sources. (arXiv:1906.07263v1 [physics.ins-det])

We demonstrate X-ray phase contrast microscopy performed at the European X-ray Free-Electron Laser sampled at 1.128 MHz rate. We have applied this method to image stochastic processes induced by an optical laser incident on water-filled capillaries with micrometer scale spatial resolution. The generated high speed water jet, cavitation formation and annihilation in water and glass, as well as glass explosions are observed. The comparison between XFEL and previous synchrotron MHz microscopy shows the superior contrast and spatial resolution at the XFEL over the synchrotron. This work opens up new possibilities for the characterization of dynamic stochastic systems on nanosecond to microsecond time scales at megahertz rate with object velocities up to few kilometers per second using X-ray Free-Electron Laser sources.

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18.06.2019
16:55 3dnewsНовая статья: HP Neverstop Laser 1200w – печать без картриджа или НСПЧ для лазерника

Качественная монохромная печать офисных документов на лазерном принтере без картриджа – звучит заманчиво! У новой модели МФУ от HP действительно нет тонер-картриджа, а стоимость отпечатка в десятки раз ниже, чем у любого другого лазерного принтера. Как этого удалось добиться и есть ли у новинки недостатки – читайте в нашем обзоре

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09:48 Arxiv.org PhysicsReconstruction of attosecond pulses in the presence of interfering dressing fields using the 100 kHz ELI-ALPS HR-1 laser system. (arXiv:1906.07059v1 [physics.atom-ph])

Attosecond Pulse Trains (APT) generated by high-harmonic generation (HHG) of high-intensity near-infrared (IR) laser pulses have proven valuable for studying the electronic dynamics of atomic and molecular species. However, the high intensities required for high-photon-energy, high-flux HHG usually limit the class of adequate laser systems to repetition rates below 10~kHz. Here, APT's generated from the 100 kHz, 160 W, 40 fs laser system (HR1) of the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI-ALPS) are reconstructed using the Reconstruction of Attosecond Beating By Interference of two-photon Transitions (RABBIT) technique. These experiments constitute the first attosecond time-resolved photoelectron spectroscopy measurements performed at 100 kHz repetition rate and the first attosecond experiments performed at ELI-ALPS. These RABBIT measurements were taken with an

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09:48 Arxiv.org PhysicsFusion hindrance effects in laser-induced non-neutral plasmas. (arXiv:1906.06724v1 [nucl-th])

Inertial confinement fusion hotspots and cluster Coulomb explosion plasmas may develop a positive net electric charge. The Coulomb barrier penetrability and the rate of nuclear fusion reactions at ultra-low energies ($\lesssim 10$ keV) are altered by such an environment. These effects are here studied via the screening potential approach. Approximate analytical results are developed by evaluating the average screening potential for some scenarios of interest. It is found that fusion is hindered for reactions between thermal fuel nuclei, while an enhancement is expected for secondary and "beam-target" reactions. Depending on the plasma conditions, the variations can be relevant even for relatively small net charges (several % difference or more in the fusion rate for an average net charge per nucleus of $10^{-5}$ proton charges).

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17.06.2019
05:15 Arxiv.org PhysicsTerahertz vortex wave generation in air plasma by two-color femtosecond laser pulses. (arXiv:1906.06243v1 [physics.plasm-ph])

We investigate the generation of broadband terahertz (THz) pulses with phase singularity from air plasmas created by fundamental and second harmonic laser pulses. We show that when the second harmonic beam carries a vortex charge, the THz beam acquires a vortex structure as well. A generic feature of such THz vortex is that the intensity is modulated along the azimuthal angle, which can be attributed to the spatially varying relative phase difference between the two pump harmonics. Fully space and time resolved numerical simulations reveal that transverse instabilities of the pump further affect the emitted THz field along nonlinear propagation, which produces additional singularities resulting in a rich vortex structure. The predicted intensity modulation is experimentally demonstrated with a thermal camera, in excellent agreement with simulation results. The presence of phase singularities

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05:15 Arxiv.org PhysicsNovel signatures of dark matter in laser-interferometric gravitational-wave detectors. (arXiv:1906.06193v1 [astro-ph.IM])

Dark matter may induce apparent temporal variations in the physical "constants", including the electromagnetic fine-structure constant and fermion masses. In particular, a coherently oscillating classical dark-matter field may induce apparent oscillations of physical constants in time, while the passage of macroscopic dark-matter objects (such as topological defects) may induce apparent transient variations in the physical constants. In this paper, we point out several new signatures of the aforementioned types of dark matter that can arise due to the geometric asymmetry created by the beam-splitter in a two-arm laser interferometer. These new signatures include dark-matter-induced time-varying size changes of a freely-suspended beam-splitter and associated time-varying shifts of the main reflecting surface of the beam-splitter that splits and recombines the laser beam, as well as

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05:15 Arxiv.org PhysicsAbsorption and opacity threshold for a thin foil in a strong laser field. (arXiv:1906.05902v1 [physics.plasm-ph])

According to simulations, a commonly accepted threshold for a transition from transparency to opaqueness of a thin foil interacting with a strong circularly polarized laser pulse needs a refinement. Here we reestablish such a threshold condition by properly taking into account the dominance of laser absorption. Our model is confirmed by PIC simulations and predicts that the threshold value is less sensitive to the laser pulse amplitude than assumed previously. Interaction with an opaque foil leads to a steepening of the laser pulse front, and this can be important for applications.

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15.06.2019
14:44 LiveScience.comScientists Develop New Laser That Can Find and Destroy Cancer Cells in the Blood

This technology can screen the blood from above the skin.

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14.06.2019
15:53 Phys.orgLaser trick produces high-energy terahertz pulses

A team of scientists from DESY and the University of Hamburg has achieved an important milestone in the quest for a new type of compact particle accelerator. Using ultra-powerful pulses of laser light, they were able to produce particularly high-energy flashes of radiation in the terahertz range having a sharply defined wavelength (color). Terahertz radiation is to open the way for a new generation of compact particle accelerators that will find room on a lab bench. The team headed by Andreas Maier and Franz Kärtner from the Hamburg Center for Free-Electron Laser Science (CFEL) is presenting its findings in the journal Nature Communications. CFEL is jointly run by DESY, the University of Hamburg and the Max Planck Society.

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