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https://www.readbyqxmd.com/read/29350964/generation-of-high-power-high-intensity-short-x-ray-free-electron-laser-pulses
#1
Marc W Guetg, Alberto A Lutman, Yuantao Ding, Timothy J Maxwell, Franz-Josef Decker, Uwe Bergmann, Zhirong Huang
X-ray free-electron lasers combine a high pulse power, short pulse length, narrow bandwidth, and high degree of transverse coherence. Any increase in the photon pulse power, while shortening the pulse length, will further push the frontier on several key x-ray free-electron laser applications including single-molecule imaging and novel nonlinear x-ray methods. This Letter shows experimental results at the Linac Coherent Light Source raising its maximum power to more than 300% of the current limit while reducing the photon pulse length to 10 fs...
January 5, 2018: Physical Review Letters
https://www.readbyqxmd.com/read/29347097/extreme-and-superextreme-events-in-a-loss-modulated-co_-2-laser-nonlinear-resonance-route-and-precursors
#2
Cristian Bonatto, Antonio Endler
We investigate the occurrence of extreme and rare events, i.e., giant and rare light pulses, in a periodically modulated CO_{2} laser model. Due to nonlinear resonant processes, we show a scenario of interaction between chaotic bands of different orders, which may lead to the formation of extreme and rare events. We identify a crisis line in the modulation parameter space, and we show that, when the modulation amplitude increases, remaining in the vicinity of the crisis, some statistical properties of the laser pulses, such as the average and dispersion of amplitudes, do not change much, whereas the amplitude of extreme events grows enormously, giving rise to extreme events with much larger deviations than usually reported, with a significant probability of occurrence, i...
July 2017: Physical Review. E
https://www.readbyqxmd.com/read/29347053/radiation-pressure-driven-ion-weibel-instability-and-collisionless-shocks
#3
A Grassi, M Grech, F Amiranoff, A Macchi, C Riconda
The Weibel instability from counterstreaming plasma flows is a basic process highly relevant for collisionless shock formation in astrophysics. In this paper we investigate, via two- and three-dimensional simulations, suitable configurations for laboratory investigations of the ion Weibel instability (IWI) driven by a fast quasineutral plasma flow launched into the target via the radiation pressure of an ultra-high-intensity laser pulse ("hole-boring" process). The use of S-polarized light at oblique incidence is found to be an optimal configuration for driving IWI, as it prevents the development of surface rippling observed at normal incidence that would lead to strong electron heating and would favor competing instabilities...
September 2017: Physical Review. E
https://www.readbyqxmd.com/read/29346907/fast-electrons-generated-by-quasistatic-electric-fields-of-a-fs-laser-pulse-induced-plasma
#4
F Kleeschulte, B Hagmeister, D Hemmers, G Pretzler
We present a new acceleration mechanism for electrons taking place during the interaction of an ultrashort, nonrelativistic laser pulse with a plasma generated at the surface of a solid density target. In our experiments, the plasma is created by a laser pulse with femtosecond duration and an energy of about 1 mJ focused to intensities of above 10^{17}W/cm^{2}. We observe that the electron energies acquired by this mechanism exceed the ponderomotive potential of the laser by an order of magnitude. This result was reproduced and quantitatively confirmed by particle-in-cell simulations, which further revealed that the observed electron acceleration is based on quasistatic electric fields caused by the space charges of ponderomotively preaccelerated electrons...
September 2017: Physical Review. E
https://www.readbyqxmd.com/read/29343750/multi-wavelength-growth-of-nanosecond-laser-induced-surface-damage-on-fused-silica-gratings
#5
Maxime Chambonneau, Laurent Lamaignère
The nanosecond laser-induced damage growth phenomenon on the exit surface of fused silica grating is investigated at 1064 nm and 355 nm separately and also simultaneously. Experiments are first carried out on damage sites on a plane fused silica sample showing two different morphologies, and a damage type is selected for ensuring the repeatability of the subsequent tests. Comparing the mono-wavelength growth results on a grating and a plane fused silica sample, the periodic surface structure is found to be an aggravating factor for damage growth...
January 17, 2018: Scientific Reports
https://www.readbyqxmd.com/read/29341630/terahertz-sum-frequency-excitation-of-a-raman-active-phonon
#6
Sebastian Maehrlein, Alexander Paarmann, Martin Wolf, Tobias Kampfrath
In stimulated Raman scattering, two incident optical waves induce a force oscillating at the difference of the two light frequencies. This process has enabled important applications such as the excitation and coherent control of phonons and magnons by femtosecond laser pulses. Here, we experimentally and theoretically demonstrate the so far neglected up-conversion counterpart of this process: THz sum-frequency excitation of a Raman-active phonon mode, which is tantamount to two-photon absorption by an optical transition between two adjacent vibrational levels...
September 22, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/29339756/shot-by-shot-characterization-of-focused-x-ray-free-electron-laser-pulses
#7
Amane Kobayashi, Yuki Sekiguchi, Tomotaka Oroguchi, Masaki Yamamoto, Masayoshi Nakasako
X-ray free electron lasers (XFEL) provide intense and almost coherent X-ray pulses. They are used for various experiments investigating physical and chemical properties in materials and biological science because of their complete coherence, high intensity, and very short pulse width. In XFEL experiments, specimens are irradiated by XFEL pulses focused by mirror optics. The focused pulse is too intense to measure its coherence by placing an X-ray detector on the focal spot. Previously, a method was proposed for evaluating the coherence of focused pulses from the visibility of the diffraction intensity of colloidal particles by the speckle visibility spectroscopy (SVS)...
January 16, 2018: Scientific Reports
https://www.readbyqxmd.com/read/29336034/quantitative-evaluation-of-collagen-and-elastic-fibers-after-intense-pulsed-light-treatment-of-mouse-skin
#8
Luciana L Faucz, Sonia E Will, Consuelo J Rodrigues, Henrique Hesse, Angelina C Moraes, Durvanei A Maria
BACKGROUND AND OBJECTIVE: The aging of human skin includes intrinsic aging and photo-aging, which are characterized by a decrease in collagen and the deposition of abnormal elastic fibers. Intense pulsed light (IPL) sources are widely used in medicine to treat various cosmetic problems, including photo-damaged skin. Few studies have examined the microscopic changes produced by IPL. The objective of this study was to quantitatively evaluate the effects of IPL on collagen and elastic fibers in mice...
January 16, 2018: Lasers in Surgery and Medicine
https://www.readbyqxmd.com/read/29335602/in-situ-single-shot-diffractive-fluence-mapping-for-x-ray-free-electron-laser-pulses
#9
Michael Schneider, Christian M Günther, Bastian Pfau, Flavio Capotondi, Michele Manfredda, Marco Zangrando, Nicola Mahne, Lorenzo Raimondi, Emanuele Pedersoli, Denys Naumenko, Stefan Eisebitt
Free-electron lasers (FELs) in the extreme ultraviolet (XUV) and X-ray regime opened up the possibility for experiments at high power densities, in particular allowing for fluence-dependent absorption and scattering experiments to reveal non-linear light-matter interactions at ever shorter wavelengths. Findings of such non-linear effects are met with tremendous interest, but prove difficult to understand and model due to the inherent shot-to-shot fluctuations in photon intensity and the often structured, non-Gaussian spatial intensity profile of a focused FEL beam...
January 15, 2018: Nature Communications
https://www.readbyqxmd.com/read/29330510/shaping-and-controlled-fragmentation-of-liquid-metal-droplets-through-cavitation
#10
M S Krivokorytov, Q Zeng, B V Lakatosh, A Yu Vinokhodov, Yu V Sidelnikov, V O Kompanets, V M Krivtsun, K N Koshelev, C D Ohl, V V Medvedev
Targeting micrometer sized metal droplets with near-infrared sub-picosecond laser pulses generates intense stress-confined acoustic waves within the droplet. Spherical focusing amplifies their pressures. The rarefaction wave nucleates cavitation at the center of the droplet, which explosively expands with a repeatable fragmentation scenario resulting into high-speed jetting. We predict the number of jets as a function of the laser energy by coupling the cavitation bubble dynamics with Rayleigh-Taylor instabilities...
January 12, 2018: Scientific Reports
https://www.readbyqxmd.com/read/29328248/filamentation-free-self-compression-of-mid-infrared-pulses-in-birefringent-crystals-with-second-order-cascading-enhanced-self-focusing-nonlinearity
#11
Rosvaldas Šuminas, Gintaras Tamošauskas, Audrius Dubietis
We experimentally demonstrate virtually lossless, filamentation-free and energy-scalable more than three-fold self-compression of mid-infrared laser pulses at 2.1 μm in a birefringent medium (β-BBO crystal), which stems from favorable interplay between the second-order cascading-enhanced self-phase modulation and anomalous group velocity dispersion. By choosing an appropriate input beam diameter and intensity, the self-compression down to sub-30 fs pulse widths with gigawatt peak power is achieved without the onset of beam filamentation and associated nonlinear losses due to the multiphoton absorption, yielding the energy throughput greater than 86%...
January 15, 2018: Optics Letters
https://www.readbyqxmd.com/read/29328208/absorption-of-laser-plasma-in-competition-with-oscillation-currents-for-a-terahertz-spectrum
#12
Xiaolu Li, Ya Bai, Na Li, Peng Liu
We generate terahertz radiation in a supersonic jet of nitrogen molecules pumped by intense two-color laser pulses. The tuning of terahertz spectra from blue shift to red shift is observed by increasing laser power and stagnation pressure, and the red shift range is enlarged with the increased stagnation pressure. Our simulation reveals that the plasma absorption of the oscillation currents and expanded plasma column owing to increased laser intensity and gas number density are crucial factors in the recurrence of the red shift of terahertz spectra...
January 1, 2018: Optics Letters
https://www.readbyqxmd.com/read/29328196/anisotropy-of-nonlinear-optical-absorption-of-lbo-crystals-at-355%C3%A2-%C3%A2-nm
#13
Oleg I Vershinin, Aleksey V Konyashkin, Oleg A Ryabushkin
The dependence of the nonlinear optical absorption coefficients on the intensity and polarization of pulsed laser radiation at 355 nm was investigated for lithium triborate (LBO) crystals using the piezoelectric resonance laser calorimetry.
January 1, 2018: Optics Letters
https://www.readbyqxmd.com/read/29327088/amplification-of-pressure-waves-in-laser-assisted-endodontics-with-synchronized-delivery-of-er-yag-laser-pulses
#14
Nejc Lukač, Matija Jezeršek
When attempting to clean surfaces of dental root canals with laser-induced cavitation bubbles, the resulting cavitation oscillations are significantly prolonged due to friction on the cavity walls and other factors. Consequently, the collapses are less intense and the shock waves that are usually emitted following a bubble's collapse are diminished or not present at all. A new technique of synchronized laser-pulse delivery intended to enhance the emission of shock waves from collapsed bubbles in fluid-filled endodontic canals is reported...
January 11, 2018: Lasers in Medical Science
https://www.readbyqxmd.com/read/29323449/enhanced-ultrafast-nonlinear-optical-response-in-ferrite-core-shell-nanostructures-with-excellent-optical-limiting-performance
#15
Sreekanth Perumbilavil, Alberto López-Ortega, Gaurav Kumar Tiwari, Josep Nogués, Tamio Endo, Reji Philip
Nonlinear optical nanostructured materials are gaining increased interest as optical limiters for various applications, although many of them suffer from reduced efficiencies at high-light fluences due to photoinduced deterioration. The nonlinear optical properties of ferrite core/shell nanoparticles showing their robustness for ultrafast optical limiting applications are reported. At 100 fs ultrashort laser pulses the effective two-photon absorption (2PA) coefficient shows a nonmonotonic dependence on the shell thickness, with a maximum value obtained for thin shells...
January 11, 2018: Small
https://www.readbyqxmd.com/read/29317689/high-energy-short-duration-bursts-of-coherent-terahertz-radiation-from-an-embedded-plasma-dipole
#16
Kyu Been Kwon, Teyoun Kang, Hyung Seon Song, Young-Kuk Kim, Bernhard Ersfeld, Dino A Jaroszynski, Min Sup Hur
Emission of radiation from electrons undergoing plasma oscillations (POs) at the plasma frequency has attracted interest because of the existence of intriguing and non-trivial coupling mechanism between the electrostatic PO and the emitted electromagnetic wave. While broadband emission from plasma waves in inhomogeneous plasma is well known, the underlying physics of narrowband emission at the plasma frequency observed in experiments and in solar radio-bursts is obscure. Here we show that a spatially-localized plasma dipole oscillation (PDO) can be generated when electrons are trapped in a moving train of potential wells produced by the ponderomotive force of two slightly detuned laser pulses that collide in plasma and give rise to a burst of quasi-monochromatic radiation...
January 9, 2018: Scientific Reports
https://www.readbyqxmd.com/read/29302026/acetylacetone-photodynamics-at-a-seeded-free-electron-laser
#17
R J Squibb, M Sapunar, A Ponzi, R Richter, A Kivimäki, O Plekan, P Finetti, N Sisourat, V Zhaunerchyk, T Marchenko, L Journel, R Guillemin, R Cucini, M Coreno, C Grazioli, M Di Fraia, C Callegari, K C Prince, P Decleva, M Simon, J H D Eland, N Došlić, R Feifel, M N Piancastelli
The first steps in photochemical processes, such as photosynthesis or animal vision, involve changes in electronic and geometric structure on extremely short time scales. Time-resolved photoelectron spectroscopy is a natural way to measure such changes, but has been hindered hitherto by limitations of available pulsed light sources in the vacuum-ultraviolet and soft X-ray spectral region, which have insufficient resolution in time and energy simultaneously. The unique combination of intensity, energy resolution, and femtosecond pulse duration of the FERMI-seeded free-electron laser can now provide exceptionally detailed information on photoexcitation-deexcitation and fragmentation in pump-probe experiments on the 50-femtosecond time scale...
January 4, 2018: Nature Communications
https://www.readbyqxmd.com/read/29295735/photodynamic-therapy-interventions-in-facial-photodamage-a-systematic-review
#18
G Sanclemente, V Ruiz-Cañas, J M Miranda, A P Ferrín, P A Ramirez, G N Hernandez
INTRODUCTION: Photodynamic therapy (PDT) involves the combination of a light source and a photosensitizing agent to induce tissue damage via the generation of singlet oxygen. Although topical PDT has been approved for other indications, its use in facial photodamage is uncertain. AIMS: To assess the efficacy and safety of PDT in facial skin photoaging. METHODS: All randomized clinical trials (RCTs) evaluating the efficacy and safety of any form of topical PDT for the treatment of facial photodamage (dermatoheliosis) or photoaging in patients older than 18 years, were included...
December 30, 2017: Actas Dermo-sifiliográficas
https://www.readbyqxmd.com/read/29295599/acousto-optic-q-switched-fiber-laser-based-intra-cavity-photoacoustic-spectroscopy-for-trace-gas-detection
#19
Qinduan Zhang, Jun Chang, Qiang Wang, Zongliang Wang, Fupeng Wang, Zengguang Qin
We proposed a new method for gas detection in photoacoustic spectroscopy based on acousto-optic Q-switched fiber laser by merging a transmission PAS cell (resonant frequency f₀ = 5.3 kHz) inside the fiber laser cavity. The Q-switching was achieved by an acousto-optic modulator, achieving a peak pulse power of ~679 mW in the case of the acousto-optic modulation signal with an optimized duty ratio of 10%. We used a custom-made fiber Bragg grating with a central wavelength of 1530.37 nm (the absorption peak of C₂H₂) to select the laser wavelength...
December 25, 2017: Sensors
https://www.readbyqxmd.com/read/29286743/disentangling-intracycle-interferences-in-photoelectron-momentum-distributions-using-orthogonal-two-color-laser-fields
#20
Xinhua Xie, Tian Wang, ShaoGang Yu, XuanYang Lai, Stefan Roither, Daniil Kartashov, Andrius Baltuška, XiaoJun Liu, André Staudte, Markus Kitzler
We use orthogonally polarized two-color (OTC) laser pulses to separate quantum paths in the multiphoton ionization of Ar atoms. Our OTC pulses consist of 400 and 800 nm light at a relative intensity ratio of 10∶1. We find a hitherto unobserved interference in the photoelectron momentum distribution, which exhibits a strong dependence on the relative phase of the OTC pulse. Analysis of model calculations reveals that the interference is caused by quantum pathways from nonadjacent quarter cycles.
December 15, 2017: Physical Review Letters
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