共查询到17条相似文献,搜索用时 156 毫秒
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采用1kHz飞秒激光(脉宽148fs,中心波长775nm)对石英衬底的金膜的烧蚀过程进行了研究.单脉冲与多脉冲的烧蚀阈值可以通过烧蚀点的直径平方与所用的激光能流的关系曲线获得.通过累积能流和烧蚀脉冲数的关系,可以得到金膜的脉冲累积因子.采用飞秒激光加工材料的一些特点可以合理解释单脉冲阈值附近获得的一些实验现象. 相似文献
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半导体可饱和吸收镜(SESAM)在飞秒脉冲激光器锁模中,是一种非常有潜力的锁模启动器.其损伤闽值的高低与连续锁模阈值比较相近,极易损伤,因而研究在飞秒激光作用下SESAM的损伤阈值很有必要.利用飞秒激光分别对单晶硅、自然生长SESAM及腐蚀后SESAM在50fs、200fs和400fs脉宽下进行了表面烧蚀研究,并且保证每次烧蚀的激光脉;中个数为50个.结果发现单晶硅和自然生长SESAM的损伤阈值要高于腐蚀乓SESAM,随脉宽的增加而逐渐增大;而腐蚀后SESAM的损伤阈值却随脉宽的增加而逐渐减小. 相似文献
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利用Nd:YAG纳秒激光(波长分别为355、532和1 064 nm)辐照由电子束蒸发技术制备的类金刚石(DLC)薄膜,通过光学显微镜、光学轮廓仪和拉曼光谱仪等分析了辐照后的薄膜样品,结果表明:不同波长的单脉冲激光辐照时,DLC膜的激光损伤阈值不同;同一波长的多脉冲激光辐照时,损伤阈值低于单脉冲辐照阈值;脉冲激光辐照对DLC膜具有改性作用,受辐照薄膜区域表层发生了石墨化、剥落和气化效应,致使DLC膜表面出现了隆起和弹坑,隆起高度和弹坑深度与激光能量密度大小和脉冲个数有关. 相似文献
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激光表面加工是一种能够有效降低陶瓷材料表面粗糙度的方法,为了研究脉冲激光与陶瓷材料作用后表面形貌演变过程及激光工艺参数对表面粗糙度的影响,本文通过有限元法建立了瞬态二维轴对称数值模型,研究了单脉冲、多脉冲激光作用于氧化陶瓷表面形貌的演变过程及激光工艺参数对表面粗糙度的影响。结果表明:单脉冲激光对材料表面具有显著的平滑效果;多脉冲激光加工在脉冲2~3次时具有最好的平滑效果,继续增加脉冲数量,熔池内的表面轮廓开始向下凹陷,表面平滑效果减弱;采用不同工艺参数加工时,过大的频率、脉宽、激光功率都会导致材料表面粗糙度增加。当表面温度处于熔化温度与蒸发温度之间,熔池内流体以毛细力为主要驱动力,促使表面逐渐平滑;当表面温度超过蒸发温度时,熔池内流体受反冲压力挤压,促使表面粗糙。实验与模拟结果对比表明,该模型具有较高的准确性。 相似文献
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《功能材料》2015,(17)
开展了飞秒激光对GaAs太阳能电池表面辐照损伤的试验研究。研究结果表明,在能量密度0.27J/cm2时,飞秒激光对GaAs太阳能电池表面开始造成损伤,其损伤程度随着激光能量密度的增加而增加;在相同激光能量密度的条件下,其损伤程度随着扫描速度的增加而减小。采用光学显微镜对其表面损伤形貌进行分析发现,其烧蚀面积随着激光能量密度的增大而不断增大,这是因为飞秒激光的光斑能量成高斯型分布。根据烧蚀区域光斑直径与脉冲能量的关系,对GaAs太阳能电池表层TiO2/SiO2薄膜的损伤阈值进行了理论计算,其阈值为0.35J/cm2大于实验测试结果0.27J/cm2。这可能是由于理论计算中对激光光斑模式的简化以及材料特性均化处理等不确定度因素影响的结果。 相似文献
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High-energy femtosecond laser pulses propagating in the atmosphere undergo self-focusing resulting in the appearance of the phenomenon of filamentation. We observed an extra-attenuation of such (terawatt) femtosecond laser pulses propagating in the atmosphere when compared with long pulses (200 ps) with the same energy. This is because, in contrast to the linear propagation of the long pulse, the input femtosecond laser pulse is attenuated owing to either absorption through multiphoton ionization/tunnel ionization or to scattering on the laser-induced plasma; self-phase-modulation and self-steepening further convert partially the energy initially contained in the fundamental bandwidth into the broad side bands of the laser, becoming eventually a white-light laser pulse (supercontinuum). The experimental data allow us to extract an effective extra-attenuation coefficient for an exponential decay of the input pulse energy with the propagation distance. Such a coefficient allows us to estimate an upper bound of the filament length under the experimental conditions used. More generally, our observation leads to a new technique to remotely detect light filaments in the atmosphere. 相似文献
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Laser ablation of single-crystalline indium phosphide (InP) was performed in air by means of linearly polarized Ti : sapphire femtosecond pulses (800 nm, 130 fs, 10 Hz). As a result of the irradiation with a variable number of laser pulses per spot (N /spl les/ 5), several morphological changes (crater formation, rim formation, ripple structures, and cones) were observed. These effects were explored using force modulation microscopy (FMM), a technique based on scanning force microscopy, allowing the simultaneous imaging of both topography and local stiffness at a high lateral resolution. The first laser pulse induces the formation of a protruding rim (height < 20 nm, width /spl ap/ 300 nm) bordering the ablated crater. A Fourier analysis of the multipulse generated topographies reveals the formation of wavelength-sized periodic ripples (modulation depth < 100 nm) with an orientation perpendicular to that of the electric field vector of the laser radiation. Besides these morphological alterations, material modifications were also observed in the irradiated regions by means of the FMM technique. Within the ablated craters, local stiffness variations were found revealing an inhomogeneous material composition/structure as a consequence of the femtosecond pulse laser treatment. 相似文献
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Nanosecond and femtosecond laser ablation of brass: particulate and ICPMS measurements 总被引:1,自引:0,他引:1
Femtosecond and nanosecond lasers were compared for ablating brass alloys. All operating parameters from both lasers were equal except for the pulse duration. The ablated aerosol vapor was collected on silicon substrates for particle size measurements or sent into an inductively coupled plasma mass spectrometer. The diameters and size distribution of particulates were measured from scanning electron microscope (SEM) images of the collected ablated aerosol. SEM measurements showed that particles ablated using nanosecond pulses were single spherical entities ranging in diameter from several micrometers to several hundred nanometers. Primary particles ablated using femtosecond ablation were approximately 100 nm in diameter but formed large agglomerates. ICPMS showed enhanced signal intensity and stability using femtosecond compared to nanosecond laser ablation. 相似文献
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High-repetition-rate (80-MHz) femtosecond infrared pulses are generated by difference frequency mixing (DFM) a femtosecond Ti:sapphire laser with a phase-locked synchronized cw mode-locked Nd:YAG picosecond laser. This DFM scheme is of particular interest for generating ultrashort near-IR pulses (~10 fs) because group velocity mismatch with a pump pulse can be ignored. The simplicity and the broad wavelength tunability (from the near IR to the mid-IR) of this scheme is demonstrated. Short (125-fs FWHM) optical pulses in the near IR around 1.5 mum are obtained with noncritical type-I phase-matched LiB(3) O(5). We also used a similar scheme to generate mid-infrared pulses at 3.0 mum with type-II phase-matched KTiOPO(4). 相似文献
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Inducing and probing non-thermal transitions in semiconductors using femtosecond laser pulses 总被引:1,自引:0,他引:1
Soon after it was discovered that intense laser pulses of nanosecond duration from a ruby laser could anneal the lattice of silicon, it was established that this so-called pulsed laser annealing is a thermal process. Although the radiation energy is transferred to the electrons, the electrons transfer their energy to the lattice on the timescale of the excitation. The electrons and the lattice remain in equilibrium and the laser simply 'heats' the solid to the melting temperature within the duration of the laser pulse. For ultrashort laser pulses in the femtosecond regime, however, thermal processes (which take several picoseconds) and equilibrium thermodynamics cannot account for the experimental data. On excitation with femtosecond laser pulses, the electrons and the lattice are driven far out of equilibrium and disordering of the lattice can occur because the interatomic forces are modified due to the excitation of a large (10% or more) fraction of the valence electrons to the conduction band. This review focuses on the nature of the non-thermal transitions in semiconductors under femtosecond laser excitation. 相似文献
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Surface-relief gratings with submicrometer modulation periods were ablated by F2-laser radiation in thin metal-oxide films to produce resonant grating waveguide structures. For 150 nm films of Nb2O5, grating amplitudes in the range of 5-50 nm could be reproducibly excised with a controlled exposure of a laser energy density and a number of pulses within a narrow processing window. Resonant coupling of 800 nm ultrashort pulsed laser light into the resulting grating waveguide structure is verified with reflection and transmission spectra and satisfactorily modeled by coupled-mode theory. The laser-fabricated grating waveguides are attractive for high damage threshold reflectors and biosensor applications. 相似文献
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A mid-infrared femtosecond optical parametric amplifier tunable in the chemically important spectral region between 3.1 and 3.9 mum (at >10-muJ idler pulse energy) has been constructed on the basis of MgO:LiNbO(3) with 7% doping. With femtosecond pumping near 800 nm (Ti:sapphire regenerative amplifier) and narrow-band (long-pulse) seeding, this simple single-stage device provides maximum conversion efficiencies of 40% and exhibits extremely low seed threshold (<10-mW peak seed power for >1-muJ idler output). The generated idler pulses are almost transform limited with <200-fs pulse duration. The pulse-to-pulse fluctuations reproduce the stability of the pump source at 1-kHz repetition rate. 相似文献