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1.
Pulse broadening of the femtosecond pulses in a Gaussian beam passing an angular disperser 总被引:4,自引:0,他引:4
A general analytical formula has been found to describe the evolution of the pulse width of the femtosecond pulses in a Gaussian beam after passing an angular disperser without the assumption of well collimation. This formula is experimentally verified by measuring the pulse width with an autocorrelator based on two-photon absorption. It is found that the effect of the spectral lateral walk-off and group delay dispersion on the pulse-width evolution, and its dependence on the distance traveled, are substantially different when the beam has not been well collimated than from when it has been collimated. These differences result from the decaying nature of the angular dispersion of the Gaussian beam sent across a distance. 相似文献
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自衍射效应在飞秒激光领域有非常重要的应用,如提高飞秒脉冲的时域对比度、作为自参考光谱干涉脉冲测量法的参考光、作为频率分辨光学开关法的信号光等.然而,具有较宽光谱带宽的飞秒激光在自衍射效应过程中产生的信号光存在明显的角色散,这给自衍射效应的应用带来不利影响.本文研究发现通过在自衍射效应的一个光路中加入等腰直角棱镜,当到棱镜的入射角为23fi时可以明显地减小飞秒激光脉冲自衍射信号的角色散.这就为以后将自衍射效应更好的应用到飞秒激光脉冲的研究提供了有用的参考. 相似文献
3.
Angular dispersion of femtosecond pulses in a Gaussian beam 总被引:2,自引:0,他引:2
The angular dispersion of spatially Gaussian laser pulses, unlike for plane waves, changes with the distance between the disperser and the observer and between the beam waist and the disperser. The formula that is derived is experimentally verified by use of a high-precision measurement technique. Because the angular dispersion of a Gaussian beam is substantially different from that of a plane wave after the same disperser, the phenomenon may be of special interest for short-pulsed laser systems, for which alignment of the stretcher-compressor system for zero residual angular dispersion is essential. 相似文献
4.
ZENG ShaoQun LUO QingMing LI DeRong & Lü XiaoHua Britton Chance Center for Biomedical Photonics Wuhan National Laboratory for Optoelectronics Huazhong University of Science Technology Wuhan China 《中国科学G辑(英文版)》2009,52(5):685-692
Acousto-optic modulation of the femtosecond laser beam has wide potential in various fields such as microscopic imaging, micromachining
and optical storage because of its rapidity, high accuracy and good repeatability. This paper reviews the latest research
on acousto-optic modulation of femtosecond laser, describes the effects of spatial and temporal dispersion of such lasers
after acousto-optic modulation, introduces the theoretical outcomes on pulse width evolution of the Gaussian laser pulses
after acousto-optic modulation, discusses the characteristics of contemporary dispersion-compensating techniques for the acousto-optic
modulation of femtosecond laser, and finally refers to the challenges of this technique.
Supported by the National Natural Science Foundation of China (Grant Nos. 60278017, 30328014, and 30370463) and the National
Basic Research Program of China (Grant No. 2004CB520804) 相似文献
5.
Mode improvement of a femtosecond laser beam by the spatially self-focusing effect in solid material
The self-focusing effect of femtosecond pulses in a thin piece of BK7 glass is researched through experiment and calculation. The spatial-mode improvement of the femtosecond laser beam is observed. Against the incident pulse with spatial wings, a Gauss-like spatial mode is obtained due to the spatially self-focusing effect in a solid material. The femtosecond pulse propagation in the thin glass plate is analyzed by the amended propagation equation, and the theoretical result shows a qualitative agreement with the experimental result. According to the analysis, the mode improvement of the femtosecond laser beam is resulted from the combination with the self-focusing and dispersion effects in the solid material. 相似文献
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实验研究了线偏振和圆偏振状态下的飞秒强激光脉冲在块状材料中的传输过程。不同偏振的激光脉冲在传输过程中得到了不同程度的光谱展宽,经色散补偿后,脉冲时域宽度均得到了压缩。详细分析了压缩脉冲的脉宽以及啁啾情况与入射激光脉冲能量之间的关系,比较了飞秒激光在线偏振及圆偏振情况下的不同压缩效果。在线偏振入射光情况下得到了最短21fs的压缩脉冲宽度,在圆偏振情况下得到的最短脉冲宽度为22fs。实验结果表明,这种光谱展宽与色散补偿方式对圆偏振光同样适用,而且圆偏振的入射激光将更有利于对更高能量的脉冲进行压缩。在色散补偿量相同的情况下,压缩效果随入射脉冲能量变化的规律符合理论估计。 相似文献
8.
Yu. E. Geints A. A. Zemlyanov 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(3):745-754
Focused propagation of high-power femtosecond laser radiation in air is
considered. Based on numerical solution of the nonlinear Schr?dinger
equation for complex envelope of light wave electric field, evolution of the
beam effective radius is studied. The dependence of the effective (rms) size
of a focal spot and the maximally achievable intensity of laser radiation at
focal waist on the initial pulse power is established. It is shown that
focal spot of tightly focused intensive ultrashort laser radiation can
change its size during the pulse passage through the beam waist. This is the
consequence of pulse intensity clamping in region of beam focusing caused by
gas photoionization and plasma producing. This may prevent laser intensity
from its further growth in the focal region and arrest the transversal
compression of the beam in the linear focus as a whole. 相似文献
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A. A. Zemlyanov Y. E. Geints 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(2):349-357
The generic scenario of intense femtosecond laser pulse propagation in the
air from the viewpoint of evolution of its integral effective parameters
(energy transfer coefficient, effective radius, effective duration, limiting
angular divergence) is considered. The analysis of variation of the
effective parameters along the propagation path in the single and multiply
filamentation scenarios based on numerical calculations is presented. It is
shown that the process of self-action of the ultrashort radiation is
characterized by the formation in a medium of the nonlinearity layer, after
which optical pulse propagates quasi-linearly with the limiting angular
divergence that depends mainly on initial pulse power. The effective pulse
temporal duration and the effective beam radius increase after the passage
through the nonlinearity layer, and their values are mostly determined by
the initial beam power also. The coefficient of energy transmission of
femtosecond laser radiation is lower than in the linear medium and has a
tendency to decrease with the increase of the pulse power. 相似文献
11.
K. Venkatakrishnan B. Tan L. H. K. Koh B. K. A. Ngoi 《Optics and Lasers in Engineering》2002,38(6):122-432
With the rise in demand for miniaturized features with better acute edge acuity and negligible thermal damage zone, one of the key vital areas lies in the refinement of the quality of the laser beam itself. Spatial filter is routinely used in optical micromachining systems to smoothen the Gaussian profile of the machining spot in order to obtain a feature of the desired quality. However, its profile smoothening effect has never been investigated for femtosecond pulsed laser micromachining process since the extremely high peak power of femtosecond pulses will cause damage on the filtering aperture of spatial filter. During the development of an acousto-optical micromachining system using femtosecond pulses, we found that if the damage of the filtering aperture can be circumvented, spatial filter can improve the machining quality of femtosecond pulse ablation, especially when ablation is conducted at low-fluency range (just above the ablation threshold fluency). In this paper, we investigate and demonstrate both the improvement and potential that beam refinement can bring about. In our experiment, a series of test patterns were ablated with a 400 nm second-harmonic Ti:Sapphire femtosecond laser of 150 fs duration at varying pulse energy ranging from 31 to 39 nJ. The specimen used in the experiment is a platinum- (Pt) sputtered coating of 100 nm thickness on a quartz substrate. The results show a significant improvement in the constancy of the shape as well as the size of ablated feature, revealing an improved beam profile and beam energy distribution due to spatial filtering. 相似文献
12.
Self-focusing of Hermite–Gaussian laser beams in plasma under plasma density ramp has been investigated. It is known that a laser beam shows an oscillatory self-focusing and defocusing behavior with the propagation distance. To overcome the defocusing, localized upward plasma density ramp is introduced, so that the laser beam attains a minimum spot size and maintains it with only a mild ripple. The density ramp could be important for the self-focusing of a Hermite–Gaussian laser by choosing the laser and plasma parameters appropriately. Self-focusing becomes stronger as the propagation distance increases. The behavior of beam-width parameters with the distance of propagation is presented graphically. 相似文献
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WANG Zhaoying LIN Qiang NI Jie 《Chinese Journal of Lasers》2001,10(6):432-438
1 Introduction ItiswellknownthatthefundamentalGaussianbeamisnottheexactsolutionofMaxwell′sequations,butanapproximatesolutionofthewaveequationundertheconditionofslowly varyingenvelopeapproximation[1] .Theparaxialapproximationisnolongervalidwhenthebeamwai… 相似文献
15.
By using the methods of Hertz vector and angular spectrum transormation, the exact solution of non-paraxial elliptical Gaussion beam with general astigmatism based on Maxwell′s equations is obtained. We discussed its propagation characteristics. The results show that the orientation of the elliptical beam spot changes continuously as the beam propagates through isotropic media. Splitting or coupling of beam spots may occur for different initial spot size. This is very different from that of paraxial elliptical Gaussian beam. 相似文献
16.
A method for the measurement of the spatial distribution of birefringence, caused by intense femtosecond laser pulses in condensed plasma, is presented for the case of a Gaussian laser beam. For that only two light intensities are to be measured on the probe beam in a polariscope. 相似文献
17.
Because of their extremely high instantaneous powers, femtosecond lasers can color many nominally transparent materials. Although the excitations responsible for this defect formation occur on subpicosecond time scales, subsequent interactions between the resulting electronic and lattice defects complicate the evolution of color center formation and decay. These interactions must be understood in order to account for the long-term behavior of coloration. In this work, we probe the evolution of color centers generated by femtosecond laser radiation in potassium chloride and potassium bromide single crystals on time scales from microseconds to hundreds of seconds. By using an appropriately chosen probe laser focused through the femtosecond laser spot, we follow the changes in coloration due to individual or multiple femtosecond pulses and the evolution of that coloration for long times after femtosecond laser radiation is terminated. 相似文献
18.
The self-guiding of femtosecond laser pulses in air is investigated. For powers close to the threshold for self-focusing, we show that the balance between the nonlinear focusing of the beam and its defocusing by multiphoton sources produces a new kind of solitonlike structure. Over considerably long distances, the radial profile of the pulse relaxes to a steady-state shape, whereas its temporal profile shrinks along propagation. The influence of the normal group-velocity dispersion is finally discussed. 相似文献
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文章报导了基于大基模体积的高能量飞秒钛宝石激光再生放大器的设计与实验研究,在重复频率10 Hz、抽运能量60 mJ的激励下,得到了单脉冲能量17.4 mJ的种子脉冲放大结果,压缩后的脉冲宽度为40.6 fs,能量为13.9 mJ.借助于此大基模体积再生腔,仅增加一级多通放大,实现了峰值功率达1.9 TW飞秒激光脉冲输出.结果表明,大模体积再生放大不仅降低了后续放大对抽运能量的要求,也可以单独压缩实现再生腔直接输出10 mJ量级的飞秒激光脉冲,是大能量高峰值功率飞秒激光系统的优质前端. 相似文献