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Intensed pulsed laser

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https://www.readbyqxmd.com/read/28081112/electronic-states-of-defect-with-impurity-and-infrared-emission-on-black-silicon-prepared-by-an-ns-laser
#1
Zhong-Mei Huang, Wei-Qi Huang, Zui-Min Jiang, Shi-Rong Liu, Xue-Ke Wu, Chao-Jian Qin
It is found that the optimum annealing temperature is about 1000°C for the infrared emission of defect states at room temperature on black silicon (BS) prepared by using a nanosecond-pulsed laser. In addition, it is observed that the suitable annealing time is 6∼8  min at 1000°C for the emission on the BS. The crystallizing proceeding in annealing on the BS can be used to explain the above annealing effect. It is interesting that the emission band becomes intensive and broader on the BS prepared in oxygen atmosphere than that prepared in vacuum in the analysis of photoluminescence spectra, where the electronic states localized at the defects from D1 to D4 doped with oxygen play an important role in the emission with the broader band which are obviously enhanced in the room temperature...
January 15, 2017: Optics Letters
https://www.readbyqxmd.com/read/28081104/intracavity-stretcher-for-chirped-pulse-amplification-in-high-power-laser-systems
#2
Hartmut Liebetrau, Marco Hornung, Sebastian Keppler, Marco Hellwing, Alexander Kessler, Frank Schorcht, Joachim Hein, Malte C Kaluza
We present pulse stretching with an intracavity Offner-type pulse stretcher applied to a high-energy, short-pulse laser system. The compact intracavity design, offering a tunable stretching factor, allows the pulses to be stretched to several nanoseconds and, at the same time, to be amplified to 100 μJ. The stretched pulses have been further amplified with the high-power laser system Polaris and have been recompressed to durations as short as 102 fs, reaching peak powers of 100 TW. Furthermore, the temporal intensity contrast is investigated and compared to the formerly used stretcher setup...
January 15, 2017: Optics Letters
https://www.readbyqxmd.com/read/28081088/am-to-pm-conversion-in-a-resonant-microwave-optical-rectification-detector
#3
Brian H Kolner, Lanbing Kang
A LiNbO<sub>3</sub>-loaded microwave cavity pumped with weakly AM-modulated 30 fs optical pulses was used as a platform to investigate AM-to-PM conversion in the optical rectification process. Theoretical treatment of AM-to-PM conversion (i.e., peak-induced electrical phase deviation β<sub>i</sub> due to optical power modulation with index m) suggests that the dominant mechanism is self-group-velocity modulation due to χ<sup>(3)</sup> and cascaded χ<sup>(2)</sup> processes with a value of δ=β<sub>i</sub>/m=-151  dB, linearly dependent on the optical power at intensities of 6×10<sup>10</sup>  W/m<sup>2</sup> in a 40 mm long LiNbO<sub>3</sub> crystal...
January 15, 2017: Optics Letters
https://www.readbyqxmd.com/read/28078503/efficacy-of-pulsed-nd-yag-laser-in-the-treatment-of-patients-with-knee-osteoarthritis-a-randomized-controlled-trial
#4
Mohamed Salaheldien Mohamed Alayat, Tarek Helmy Ahmed Aly, Aly Elsayed Mohamed Elsayed, Ammar Suliman Mohamed Fadil
The purpose of this study was to investigate the effects of pulsed Nd:YAG laser plus glucosamine/chondroitin sulfate (GCS) in patients with knee osteoarthritis (KOA) by examining changes in pain and knee function, as well as synovial thickness (ST) and femoral cartilage thickness (FCT). Sixty-seven male patients participated, with a mean (SD) age of 53.85 (4.39) years, weight of 84.01 (4.70) kg, height of 171.51 (3.96) cm, and BMI of 28.56 (1.22). Group 1 was treated with high-intensity laser therapy (HILT), GCS, and exercises (HILT + GCS + EX)...
January 11, 2017: Lasers in Medical Science
https://www.readbyqxmd.com/read/28071852/environmental-and-excitation-power-effects-on-the-ratiometric-upconversion-luminescence-based-temperature-sensing-using-nanocrystalline-nayf4-yb3-er3
#5
Iko Hyppänen, Niina Perälä, Riikka Arppe, Michael Schäferling, Tero Soukka
The luminescence intensity ratio (LIR) of the green emissions of the near-infrared excited NaYF4:Yb3+,Er3+ nanocrystals is a promising method for temperature sensing. Here, the influence of excitation power density, excitation pulse length, excitation wavelength, silica shell, and solvent on the LIR and its temperature response is reported. Primary objective is to study the LIR mechanism and the impact of measurement and environmental parameters on the calibration and precision of the LIR. The LIR value is demonstrated to be unaffected by the excitation intensity in the studied range...
January 10, 2017: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
https://www.readbyqxmd.com/read/28071764/aligned-copper-nanorod-arrays-for-highly-efficient-generation-of-intense-ultra-broadband-thz-pulses
#6
S Mondal, Q Wei, W J Ding, H A Hafez, M A Fareed, A Laramée, X Ropagnol, G Zhang, S Sun, Z M Sheng, J Zhang, T Ozaki
We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with a length of 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in ≤20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies (≤20 THz) and increase of the electromagnetic pulse energy in the high-frequency range (from 20-200 THz)...
January 10, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28071681/increased-impedance-near-cut-off-in-plasma-like-media-leading-to-emission-of-high-power-narrow-bandwidth-radiation
#7
M S Hur, B Ersfeld, A Noble, H Suk, D A Jaroszynski
Ultra-intense, narrow-bandwidth, electromagnetic pulses have become important tools for exploring the characteristics of matter. Modern tuneable high-power light sources, such as free-electron lasers and vacuum tubes, rely on bunching of relativistic or near-relativistic electrons in vacuum. Here we present a fundamentally different method for producing narrow-bandwidth radiation from a broad spectral bandwidth current source, which takes advantage of the inflated radiation impedance close to cut-off in a medium with a plasma-like permittivity...
January 10, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28067265/laser-printed-nano-gratings-orientation-and-period-peculiarities
#8
Valdemar Stankevič, Gediminas Račiukaitis, Francesca Bragheri, Xuewen Wang, Eugene G Gamaly, Roberto Osellame, Saulius Juodkazis
Understanding of material behaviour at nanoscale under intense laser excitation is becoming critical for future application of nanotechnologies. Nanograting formation by linearly polarised ultra-short laser pulses has been studied systematically in fused silica for various pulse energies at 3D laser printing/writing conditions, typically used for the industrial fabrication of optical elements. The period of the nanogratings revealed a dependence on the orientation of the scanning direction. A tilt of the nanograting wave vector at a fixed laser polarisation was also observed...
January 9, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28067233/coherent-ultra-violet-to-near-infrared-generation-in-silica-ridge-waveguides
#9
Dong Yoon Oh, Ki Youl Yang, Connor Fredrick, Gabriel Ycas, Scott A Diddams, Kerry J Vahala
Short duration, intense pulses of light can experience dramatic spectral broadening when propagating through lengths of optical fibre. This continuum generation process is caused by a combination of nonlinear optical effects including the formation of dispersive waves. Optical analogues of Cherenkov radiation, these waves allow a pulse to radiate power into a distant spectral region. In this work, efficient and coherent dispersive wave generation of visible to ultraviolet light is demonstrated in silica waveguides on a silicon chip...
January 9, 2017: Nature Communications
https://www.readbyqxmd.com/read/28059773/attosecond-physics-at-the-nanoscale
#10
Marcelo F Ciappina, J Perez-Hernandez, Alexandra Landsman, William Okell, Sergey Zherebtsov, Benjamin Förg, Johannes Schötz, Lennart Seiffert, Thomas Fennel, Tahir Shaaran, Tomas Zimmermann, Alexis Chacón, Roland Guichard, Amelle Zair, John Tisch, J Marangos, Tobias Witting, Avi Braun, Stefan Maier, Luis Roso, Michael Krüger, Peter Hommelhoff, Matthias Kling, Ferenc Krausz, Maciej Lewenstein
Recently two emerging areas of research, attosecond and nanoscale physics, have started to come together. Attosecond physics deals with phenomena occurring when ultrashort laser pulses, with duration on the femto- and sub-femtosecond time scales, interact with atoms, molecules or solids. The laser-induced electron dynamics occurs natively on a timescale down to a few hundred or even tens of attoseconds, which is comparable with the optical field. For comparison, the revolution of an electron on a 1s orbital of a hydrogen atom is 152 as...
January 6, 2017: Reports on Progress in Physics
https://www.readbyqxmd.com/read/28059338/sub-picosecond-snapshots-of-fast-electrons-from-high-intensity-laser-matter-interactions
#11
R Pompili, M P Anania, F Bisesto, M Botton, M Castellano, E Chiadroni, A Cianchi, A Curcio, M Ferrario, M Galletti, Z Henis, M Petrarca, E Schleifer, A Zigler
The interaction of a high-intensity short-pulse laser with thin solid targets produces electron jets that escape the target and positively charge it, leading to the formation of the electrostatic potential that in turn governs the ion acceleration. The typical timescale of such phenomena is on the sub-picosecond level. Here we show, for the first time, temporally-resolved measurements of the first released electrons that escaped from the target, so-called fast electrons. Their total charge, energy and temporal profile are provided by means of a diagnostics based on Electro-Optical Sampling with temporal resolution below 100 fs...
December 26, 2016: Optics Express
https://www.readbyqxmd.com/read/28059321/high-resolution-three-dimensional-flash-lidar-system-using-a-polarization-modulating-pockels-cell-and-a-micro-polarizer-ccd-camera
#12
Sungeun Jo, Hong Jin Kong, Hyochoong Bang, Jae-Wan Kim, Jomsool Kim, Soungwoong Choi
An innovative flash LIDAR (light detection and ranging) system with high spatial resolution and high range precision is proposed in this paper. The proposed system consists of a polarization modulating Pockels cell (PMPC) and a micro-polarizer CCD camera (MCCD). The Pockels cell changes its polarization state with respect to time after a laser pulse is emitted from the system. The polarization state of the laser-return pulse depends on the arrival time. The MCCD measures the intensity of the returning laser pulse to calculate the polarization state, which gives the range...
December 26, 2016: Optics Express
https://www.readbyqxmd.com/read/28059250/giant-nonlinear-absorption-and-excited-carrier-dynamics-of-black-phosphorus-few-layer-nanosheets-in-broadband-spectra
#13
Runze Chen, Yuhua Tang, Xin Zheng, Tian Jiang
Layered black phosphorus nanosheets (BPNs) offer potential uses in nanoelectronic and photonics applications. This work demonstrates giant saturable absorption (SA) and two-photon absorption (TPA) of BPNs under femtosecond visible-to-mid-infrared laser-pulse excitation. In addition, the excited carrier dynamics of BPNs were also studied with ultrafast pump-probe technology. Measurements demonstrated that the nonlinear absorption properties of BPNs strongly depend on excitation wavelength and intensity. BPNs moved from SA to TPA under increasing laser intensities at 800, 1160, 1300, and 1550 nm but showed a purely TPA response at 2000 nm, as gauged by measuring BPN nonlinear absorption coefficients...
December 20, 2016: Applied Optics
https://www.readbyqxmd.com/read/28053312/laser-guided-energetic-discharges-over-large-air-gaps-by-electric-field-enhanced-plasma-filaments
#14
Francis Théberge, Jean-François Daigle, Jean-Claude Kieffer, François Vidal, Marc Châteauneuf
Recent works on plasma channels produced during the propagation of ultrashort and intense laser pulses in air demonstrated the guiding of electric discharges along the laser path. However, the short plasma lifetime limits the length of the laser-guided discharge. In this paper, the conductivity and lifetime of long plasma channels produced by ultrashort laser pulses is enhanced efficiently over many orders of magnitude by the electric field of a hybrid AC-DC high-voltage source. The AC electric pulse from a Tesla coil allowed to stimulate and maintain the highly conductive channel during few milliseconds in order to guide a subsequent 500 times more energetic discharge from a 30-kV DC source...
January 5, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28040920/mid-infrared-gas-absorption-sensor-based-on-a-broadband-external-cavity-quantum-cascade-laser
#15
Juan Sun, Hao Deng, Ningwu Liu, Hongliang Wang, Benli Yu, Jingsong Li
We developed a laser absorption sensor based on a pulsed, broadband tunable external cavity quantum cascade laser (ECQCL) centered at 1285 cm(-1). Unlike traditional infrared spectroscopy system, a quartz crystal tuning fork (QCTF) as a light detector was used for laser signal detection. Fast Fourier transform was applied to extract vibration intensity information of QCTF. The sensor system is successfully tested on nitrous oxide (N2O) spectroscopy measurements and compared with a standard infrared detector...
December 2016: Review of Scientific Instruments
https://www.readbyqxmd.com/read/28018732/safety-assessment-in-macaques-of-light-exposures-for-functional-two-photon-ophthalmoscopy-in-humans
#16
Christina Schwarz, Robin Sharma, William S Fischer, Mina Chung, Grazyna Palczewska, Krzysztof Palczewski, David R Williams, Jennifer J Hunter
Two-photon ophthalmoscopy has potential for in vivo assessment of function of normal and diseased retina. However, light safety of the sub-100 fs laser typically used is a major concern and safety standards are not well established. To test the feasibility of safe in vivo two-photon excitation fluorescence (TPEF) imaging of photoreceptors in humans, we examined the effects of ultrashort pulsed light and the required light levels with a variety of clinical and high resolution imaging methods in macaques. The only measure that revealed a significant effect due to exposure to pulsed light within existing safety standards was infrared autofluorescence (IRAF) intensity...
December 1, 2016: Biomedical Optics Express
https://www.readbyqxmd.com/read/28009557/performance-of-photoelectron-spin-polarimeters-with-continuous-and-pulsed-sources-from-storage-rings-to-free-electron-lasers
#17
T Pincelli, F Grasselli, V N Petrov, P Torelli, G Rossi
In this work the experimental uncertainties concerning electron spin polarization (SP) under various realistic measurement conditions are theoretically derived. The accuracy of the evaluation of the SP of the photoelectron current is analysed as a function of the detector parameters and specifications, as well as of the characteristics of the photoexcitation sources. In particular, the different behaviour of single counter or twin counter detectors when the intensity fluctuations of the source are considered have been addressed, leading to a new definition of the SP detector performance...
January 1, 2017: Journal of Synchrotron Radiation
https://www.readbyqxmd.com/read/28009550/design-of-a-prototype-split-and-delay-unit-for-xfel-pulses-and-their-evaluation-by-synchrotron-radiation-x-rays
#18
Jun'ya Sakamoto, Kenji Ohwada, Masahiko Ishino, Jun'ichiro Mizuki, Masami Ando, Kazumichi Namikawa
A prototype split-and-delay unit (SDU) for X-ray free-electron laser (XFEL) pulses is proposed based on the Graeff-Bonse four-Bragg-reflection interferometer by installing 12.5° slopes. The SDU can continuously provide a delay time from approximately -20 to 40 ps with a resolution of less than 26 fs. Because the SDU was constructed from a monolithic silicon crystal, alignment is straightforward. The obtained thoroughputs of the SDU reached 0.7% at 7.46 keV and 0.02% at 14.92 keV. The tunability of the delay time using the proposed SDU was demonstrated by finding the interference effects of the split X-rays, and the time resolution of the proposed SDU was evaluated using the width of the interference pattern recorded on the X-ray charge-coupled device camera by changing the energy, i...
January 1, 2017: Journal of Synchrotron Radiation
https://www.readbyqxmd.com/read/28009219/controllable-terahertz-radiation-from-a-linear-dipole-array-formed-by-a-two-color-laser-filament-in-air
#19
Zhelin Zhang, Yanping Chen, Min Chen, Zhen Zhang, Jin Yu, Zhengming Sheng, Jie Zhang
We demonstrate effective control on the carrier-envelope phase and angular distribution as well as the peak intensity of a nearly single-cycle terahertz pulse emitted from a laser filament formed by two-color, the fundamental and the corresponding second harmonics, femtosecond laser pulses propagating in air. Experimentally, such control has been performed by varying the filament length and the initial phase difference between the two-color laser components. A linear-dipole-array model, including the descriptions of both the generation (via laser field ionization) and propagation of the emitted terahertz pulse, is proposed to present a quantitative interpretation of the observations...
December 9, 2016: Physical Review Letters
https://www.readbyqxmd.com/read/28009012/strong-field-ionization-of-clusters-using-two-cycle-pulses-at-1-8%C3%A2-%C3%AE-m
#20
Bernd Schütte, Peng Ye, Serguei Patchkovskii, Dane R Austin, Christian Brahms, Christian Strüber, Tobias Witting, Misha Yu Ivanov, John W G Tisch, Jon P Marangos
The interaction of intense laser pulses with nanoscale particles leads to the production of high-energy electrons, ions, neutral atoms, neutrons and photons. Up to now, investigations have focused on near-infrared to X-ray laser pulses consisting of many optical cycles. Here we study strong-field ionization of rare-gas clusters (10(3) to 10(5) atoms) using two-cycle 1.8 μm laser pulses to access a new interaction regime in the limit where the electron dynamics are dominated by the laser field and the cluster atoms do not have time to move significantly...
December 23, 2016: Scientific Reports
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