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Collinear dual-pulse laser optical breakdown and energy deposition
摘要： A non-equilibrium model for laser-generated plasmas is used to represent collinear dual nano-second-pulse interactions. In the specific case considered, the breakdown is initiated with an ultraviolet (UV) laser pulse at 266 nm, which pre-ionizes the gas, and it is followed by a near-infrared (NIR) pulse at 1064 nm, which deposits significant energy into the ionized mixture. The model is validated against corresponding experiments, and simulation results are interrogated to understand key features of the plasma-kernel dynamics in the breakdown phase, and the initial post-breakdown vorticity and plasma-core decay.
关键词： energy deposition,laser-induced breakdown,non-equilibrium plasma,plasma dynamics,dual-pulse laser
更新于2025-09-23 15:19:57
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Thermal coagulum formation and hemostasis during repeated multipulse Nd:YAG laser treatment of cutaneous vascular lesions: animal experiment study
摘要： Laser therapy has been widely used to treat port-wine stain (PWS) and other cutaneous vascular lesions via selective photothermolysis. High incident laser fluence is always prohibited in clinic to prevent the thermal damage in normal skin tissue, leading to insufficient energy deposition on the target blood vessel and incomplete clearance of PWS lesion. In this study, repeated multipulse laser (RMPL) irradiation was proposed to induce acute thermal damage to target blood vessels with low incident fluence (40 J/cm2 for 1064-nm Nd:YAG laser). The feasibility of the method was investigated using animal models. Repeated multipulse irradiation cycles with 10-min intervals were performed in RMPL. A hamster dorsal skin chamber model with a visualization system was constructed to investigate the instant generation of thermal coagulum and relevant hemostasis by thrombus formation during and after irradiation under 1064 nm Nd:YAG single multipulse laser (SMPL) and RMPL irradiation. The diameter of the target blood vessel and the size of thermal coagula were measured before and after laser irradiation. The reflectance spectra of the dorsal skin were measured by a reflectance spectrometer during RMPL. Stasis thermal coagula that clogged the vessel lumen were generated during SMPL irradiation with low incident fluence. However, there was no acute thermal damage of blood vessels. Reflectance spectra measurement showed that the generation of thermal coagula and subsequent thrombus formation increases blood absorption by more than 10% within the first 10 min after laser irradiation. Acute vessel thermal damage could be induced in the target blood vessel by RMPL with low incident fluence of 40 J/cm2. Compared with our previous SMPL study, nearly 30% reduction in incident laser fluence was achieved by RMPL. Low fluence RMPL may be a promising approach to improve the therapeutic outcome for patients with cutaneous vascular lesions by improving energy deposition on the target blood vessel.
关键词： Thermal coagula,1064-nm Nd:YAG laser,Port-wine stain,Repeated multiple pulse laser irradiation,Thrombus formation
更新于2025-09-23 15:19:57
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Time-fractional subdiffusion model for thin metal films under femtosecond laser pulses based on Caputo fractional derivative to examine anomalous diffusion process
摘要： In this paper, the non-Fourier effects are examined in thin metal films exposed to femtosecond laser pulses. For the first time, the time-fractional subdiffusion model is presented based on the Caputo fractional derivative to examine the anomalous diffusion process in nano-scale metal films. The fractional heat conduction equation is solved numerically, using the finite difference method based on implicit scheme and the numerical results are compared to experimental data. The comparison implies that the numerical results well coincide with experimental data, proving the accuracy and suitability of fractional model to capture thermal behaviors of thin metal films heated by short-pulse laser. Furthermore, the results of time-fractional model are compared to other models including parabolic and hyperbolic two-step models. Having compared, one can be found is that the fractional model is more reliable than other models, because its results are well matched with experimental data. The use of Fourier’s law in parabolic and hyperbolic two-step model leads to deviation from experimental data which can be addressed upon applying the proposed time-fractional model in this work. Moreover, the presented time-fractional model can be effectively utilized for studying the heat transport in thin metal films under laser pulses as well as the laser heating process and its applications in engineering. Ultimately, the effect of changes in various parameters such as order of fractional derivative, laser pulse duration, metal materials (gold and chromium), gold film thickness, relaxation time and absorption depth of laser pulses are investigated on temperature response of thin metal films.
关键词： Time-fractional subdiffusion model,Short-pulse laser,Thin metal films,Caputo fractional derivative
更新于2025-09-23 15:19:57
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Spectral photoluminescence properties of YAG: Ce, R (R: Gd3+, Pr3+, Gd3+ and Pr3+) transparent fluorescent thin film prepared by pulse laser deposition
摘要： In order to overcome the shortcomings of insufficient red light component and poor thermal stability of commercial white light emitting diode (WLED), YAG:Ce, R (R: Gd3t and Pr3t) fluorescent thin films were prepared by pulse laser deposition (PLD). The composition and microstructure, photoluminescence properties, and red-enhanced mechanism of co-doped YAG fluorescent thin films, as well as the electroluminescence behavior of the corresponding WLEDs were investigated. Results showed that the doping of Pr3t caused the emission spectrum energy of Ce3t to migrate, and an emission peak appeared at 606 nm in the red region. The doping of Gd3t caused the emission spectrum of Ce3t to shift to the red region, and the main peak position of the Ce3t emission spectrum is red-shifted from 523 nm to 548 nm. The YAG:Ce,Pr,Gd fluorescent film not only realized the improvement of red light components and red-shift, but also increased the energy transmission efficiency from 33.3% to 51.9%. Moreover, results of the color coordinate analysis also showed that the co-doping of Gd3t and Pr3t made the luminescence closer to the red region, reducing the color temperatures and hues changed to warm. Thus, tri-doped transparent fluorescent thin film were prospective for WLED application.
关键词： Photoluminescence properties,Transparent thin film,Pulse laser deposition,YAG:Ce,Tri-doped YAG
更新于2025-09-23 15:19:57
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Q-Switched and Mode-Locked Nd/Cr:YAG Ceramic Pulse Laser
摘要： A mode-locked and Q-switched short pulse laser using the Nd3+/Cr3+:YAG ceramic has been constructed with a SESAM and Cr4+:YAG crystal optical switch based on excite state absorption (ESA). Laser oscillations of the pulse laser were observed experimentally. The Nd/Cr:YAG ceramic laser has a high conversion e?ciency from white light (such as lamp light or solar light) to the laser. The Nd/Cr:YAG ceramic has a higher laser gain than the Nd:YAG laser for the same pumping power. The laser oscillation can be obtained very easily. A single-mode-locked laser pulse with fast modulation on the order of 100 ps was obtained in some pump power regimes when using the Cr4+:YAG crystal. The obtained pulse duration of the short pulse was a few hundred ps. A maximum peak power of 60 kW was obtained when using a SESAM. The same level of peak power (60 kW) was also obtained when using the Cr4+:YAG crystal.
关键词： Q-switched,Nd/Cr:YAG ceramic,mode-locked,pulse laser,Cr4+:YAG crystal,SESAM
更新于2025-09-23 15:19:57
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Single-cycle THz signal accompanying laser wake in photoionized plasmas
摘要： Photoionization of an ambient gas by a weakly relativistic, femtosecond laser pulse leaves behind the pulse a ?at-top plasma column. The uniform-density core of the column is surrounded by a micron-thin shell, within which the density of plasma species falls down to zero. As the laser pulse ponderomotive force drives the wave of charge separation (the laser wake), electron ?uid velocity oscillates along this boundary layer. Coupling velocity oscillations to the transverse density gradient forms an azimuthally polarized rotational current con?ned within the boundary layer. At each radial offset, this current oscillates with a local (THz-scale) Langmuir frequency, transforming the cylindrical electrostatic plasma wave into a radially evanescent Fourier component of an electromagnetic signal. Summing up these Fourier components yields the time-domain THz signal which is (a) non-local (i.e. not phase-locked to the Langmuir oscillation at any given location), (b) contains the entire frequency band from zero to the Langmuir frequency of the density plateau, and (c) is detectable at a distance orders of magnitude larger than the plasma column radius. A few millimeters away from the column, rapid evanescence of the higher-frequency components transforms the signal into a radially polarized, single-cycle picosecond pulse with a kV m?1-scale electric ?eld. Detecting this pulse with existing (e.g. electro-optical) techniques may bring information on the ef?ciency of laser coupling to the plasma, the amplitude of wake ?elds, and the structure of the column boundary.
关键词： electromagnetic mode conversion,optical ?eld ionization,THz pulse,laser wake?eld
更新于2025-09-23 15:19:57
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[IEEE 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Rome, Italy (2019.6.17-2019.6.20)] 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Near-surface Plasma Formation in Air under Action of Two Laser Pulses at Two Wavelengths on Titanium in the Air
摘要： The spectra and structure of the near-surface plasma formation were experimentally investigated with a two-pulse laser effect at wavelengths of 532 and 1064 nm on a titanium target in the air, depending on the time interval between laser pulses and their order. The dependences of the temperature of the laser plasma on the parameters of paired laser pulses were established for laser radiation power densities of q1.064 ≤ 3.9 · 109 W/cm2, and of q0.532 =≤ 2.7 · 109 W/cm2 at wavelengths of 1064 and 532 nm, respectively. It is shown that optimal conditions for recording the erosion plasma spectra are provided with a leading effect on second harmonic radiation with a time interval between laser pulses of 4–5 μs, which is important for increasing the efficiency of the laser emission spectral analysis and laser-plasma processing of materials.
关键词： two-pulse laser effect,titanium,plasma temperature,laser plasma,spectral analysis
更新于2025-09-19 17:13:59
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Ultrashort laser based two-photon phase-resolved fluorescence lifetime measurement method
摘要： This paper presents a two-photon phase-resolved fluorescence-lifetime measurement method based on the use of an ultrashort pulse laser. The proposed method also involves the use of a lock-in amplifier to control the phase difference between the reference and fluorescence signals, thereby facilitating the use of an alternative method for determining fluorescence lifetimes. Verification of the fluorescence lifetimes as measured in this study was performed using rhodamine B and a cellular thermoprobe as samples. In this study, we assume that the fluorescence decay was monoexponential in all cases. Rhodamine B was observed to exhibit an average fluorescence lifetime of 2.15 ns, whereas a temperature sensitivity of 1.39 ns/°C over a temperature range of 33.79–37.2 °C was demonstrated for the cellular thermoprobe. These results validate the feasibility of the proposed method for accurate measurement of fluorescence lifetimes using a simple laser configuration.
关键词： rhodamine B,ultrashort pulse laser,temperature sensor,phase-resolved fluorescence-lifetime,two-photon microscopy,cellular thermoprobe
更新于2025-09-19 17:13:59
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Tandem Si Micropillar Array Photocathodes with Conformal Copper Oxide and a Protection Layer by Pulsed Laser Deposition
摘要： This work demonstrates the influence of high-quality protection layers on Si-Cu2O micropillar arrays created by pulsed laser deposition (PLD), with the goal to overcome photodegradation and achieve long-term operation during photoelectrochemical (PEC) water splitting. Sequentially, we assessed planar and micropillar device designs with various design parameters and their influence on PEC hydrogen evolution reaction. On the planar device substrates, a Cu2O film thickness of 600 nm and a Cu2O/CuO heterojunction layer with a 5:1 thickness ratio between Cu2O to CuO were found to be optimal. The planar Si/Cu2O/CuO heterostructure showed a higher PV performance (Jsc = 20 mA/cm2) compared to the planar Si/Cu2O device, but micropillar devices did not show this improvement. Multifunctional overlayers of ZnO (25 nm) and TiO2 (100 nm) were employed by PLD on Si/Cu2O planar and micropillar arrays to provide a hole-selective passivation layer that acts against photocorrosion. A micropillar Si/ITO-Au/Cu2O/ZnO/TiO2/Pt stack was compared with a planar device. Under optimized conditions, the Si/Cu2O photocathode with Pt as a HER catalyst displayed a photocurrent of 7.5 mA cm?2 at 0 V vs RHE and an onset potential of 0.85 V vs RHE, with a stable operation for 75 h.
关键词： tandem photocathode,copper oxide,Si micropillar array,hydrogen evolution reaction,pulse laser deposition
更新于2025-09-19 17:13:59
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The implementation and data analysis of an interferometer for intense short pulse laser experiments
摘要： We present an interferometry setup and the detailed fringe analysis method for intense short pulse (SP) laser experiments. The interferometry scheme was re?ned through multiple campaigns to investigate the effects of pre-plasmas on energetic electrons at the Jupiter Laser Facility at Lawrence Livermore National Laboratory. The interferometer used a frequency doubled (λ = 0.527 μm) 0.5 ps long optical probe beam to measure the pre-plasma density, an invaluable parameter to better understand how varying pre-plasma conditions affect the characteristics of the energetic electrons. The hardware of the diagnostic, data analysis and example data are presented. The diagnostic setup and the analysis procedure can be employed for any other SP laser experiments and interferograms, respectively.
关键词： short pulse laser,optical interferometry,Mach–Zehnder interferometer,picosecond probe,plasma density
更新于2025-09-19 17:13:59