[讨论]关于飞秒激光！！

methane · 发表于 2004-1-22 19:38:00

http://dutch.phys.strath.ac.uk/FRC/stuff/dictionary/dictionary.html

内容：
femtosecond oscillators
dispersion and pulse broadening
chirped-pulse amplification (including stretching compressing of pulses)
white-light generation and the optical Kerr effect
optical parametric amplifiers and infrared generation

methane · 发表于 2004-1-22 19:54:00

Review of Scientific Instruments -- December 1989 -- Volume 60, Issue 12, pp. 3597-3624

Full Text: [ PDF (5357 kB) GZipped PS ] ÷
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Ultrashort light pulses
John D. Simon
Department of Chemistry, Institute of Nonlinear Studies, University of California at San Diego, La Jolla, California 92093

(Received 9 June 1989; accepted 26 August 1989)

This article reviews the generation and amplification of ultrashort laser light pulses, p10–12 s. Current methods for generating optical pulses in the ultraviolet, visible, and infrared regions of the spectrum are described. Devices based on mode-locking techniques, as well as various novel sources for ultrashort light pulses, are examined. In addition, recent advances in using fiber optics to shape and compress optical pulses are presented. Optical amplifiers that have been developed to generate kilowatt and higher peak powers at a variety of repetition rates are described and compared. In the last section of the paper, various nonlinear optical techniques that have been developed to extend the tuning range of ultrashort laser pulses are briefly discussed. Review of Scientific Instruments is copyrighted by The American Institute of Physics.

最简单的方法就是从review看起。

methane · 发表于 2004-1-22 20:01:00

Review of Scientific Instruments -- December 1997 -- Volume 68, Issue 12, pp. 4364-4371

Full Text: [ PDF (197 kB) GZipped PS ] --------------------------------------------------------------------------------

Construction of a subpicosecond double-beam laser photolysis system utilizing a femtosecond Ti:sapphire oscillator and three Ti:sapphire amplifiers (a regenerative amplifier and two double passed linear amplifiers), and measurements of the transient absorption spectra by a pump-probe method
Toshihiro Nakayama, Yutaka Amijima, Kazuyasu Ibuki, and Kumao Hamanoue
Department of Chemistry, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606, Japan

(Received 30 April 1997; accepted 4 September 1997)

A double-beam Ti:sapphire laser photolysis system has been constructed for measurements of the subpicosecond transient absorption spectra by a pump-probe method. Although the spectroscopic characteristics tested for the practical availability are satisfactory enough, the transient absorption spectrum thus obtained exhibits an artificial time-dependent spectral change owing to the group velocity dispersion of the probing light pulse. Hence, its wavelength-dependent arrival time to the sample cell is determined utilizing the optical Kerr effect induced in carbon tetrachloride and the true transient absorption spectrum (the corrected spectrum) at a given delay-line setting is calculated by a microcomputer using a great number of uncorrected transient absorption spectra obtained at different delay-line settings. Interestingly, the corrected singlet-singlet absorption band (band C with a lifetime of 0.8 ps) obtained for the lowest excited singlet state of 9-nitroanthracene in cyclohexane really shifts with time. This can be interpreted in terms of the wide wavelength-range superposition of band C and an absorption band which increases and then decreases with rise and decay times of 0.8 and 1.8 ps, respectively; the latter band is ascribed to the absorption of 9-nitrite (or its precursor) or that of a higher excited triplet state of 9-nitroanthracene. By 400 nm biphotonic excitation of the neat solvents (cyclohexane and n-heptane), furthermore, population of their higher excited singlet states with a very short lifetime of 0.4 ps can be seen. ©1997 American Institute of Physics.

atto · 发表于 2004-1-28 14:37:00

先问一声methane是哪个实验室的?你们的系统有100mJ 100fs的输出,是确切的吗?重复频率是多少?10Hz?这个输出能量相当高了!世界上能达到这个输出的也没有几台. 100mJ/100fs=10E12W,如果聚焦一下,产生X射线是小意思了,快可以来做粒子加速了!
你查的REVIEW固然不错,但是现在世界上飞秒激光技术本省基本上已经趋于成熟,最好的REVIEW可以去看MURNANE GROUP的REVIEW,他们的SPINOFF公司为KMLabs.而另外一家做的最好的是VIENA的KRAUSZ GROUP.他们的SPINOFF公司为FEMTOLASER.当然世界上这个领域的研究者众多,各有千秋.这两个GROUP可以算是飞秒激光,超高功率激光器及其科学应用领域的领跑者.
商用方面,也有很多公司生产飞秒激光器,但大多为振荡级或一级放大,前面提到的SPECTRA PHYSICS,CMXR,还有COHERENT(收购了POSITIVE LIGHT),法国的TAHLES,还有很多大学的SPINOFF如上文提到的KML,FEMTOLASER等等.由于发明了CHIRPTED MIRRORS,FEMTOLASER可以提供10fs的OSC,而且是唯一可以提供PHASE-LOCKED TW FEWCYCLE LASER的!而这个方向在其他任何地方还只在实验室里研究!MIT也只在去年申请到5百万开始这方面的研究.
METHANE提到的张杰,他做的主要是强场物理方向的研究,包括X射线产生,等离子体物理等等,但是这方面我认为上海光机所是国内实力最强的.物理所的魏志毅,天大王清月等研究的是短脉冲的产生,西安光机所,中山大学也有超快应用方面的研究.国内做OCT的好象还没有看到.总体上说和国外的差距太大了.各位要加油啊!

methane · 发表于 2004-1-28 21:19:00

回atto：

首先谢谢你看过我对系统的描述，应该有不确切的地方，请原谅我是新手。直接引用老板的介绍：We have designed and built an experimental system which generates high energy, 150 mJ, 100x10-15 second laser pulses in the 180 nm to 1500 nm spectral range and 5 Kev to 20 Kev, 5x10-12 second intense, x-rays pulses. The laser pulses are used to initiate chemical and biological reactions and generate the x-rays.说成小于130fs比较合适，实际情况还取决于compressor最后的调节。能量的大概情况是这样，出了Tusnami osillator 80MHz/1nj,进入spitfire先strech,然后进行放大，并调节为10Hz，在这里大概会有15－20次round-trips,每次大概放大3－4倍，扣去能量的损耗，最后能得到大概1mj/1KHZ(由pump laser决定）,然后调节为10Hz（下一步pump是两台Nd :YAG)。然后进入二级放大，也是Ti:Sapphire晶体，光通过4次，大概可以得到100倍的放大。具体可以看我刚加上的图
http://bbs.oecr.com/cgi-bin/topic.cgi?forum=6topic=820show=0

我要先说明的是，我说的是最后的输出（不是一台），频率10Hz(实际可以从1kHz-1Hz调节，应该是electronic的问题）；我们主要看的也不是能量（energy）而是强度（power），正如你所计算的那样；产生的x－ray实际上包括hard x-ray，我们意识到这一点是因为，在透过0.5cm的石英玻璃，我们依然可以检测到x-ray(应该属于荧光），soft x-ray是不可能透过那么厚的玻璃的。

在应用的过程中，我们实际上遇到很多问题。

比如：
1。虽然有那么高的输出强度，也就意味着把mirror打坏的可能性增大很多，所以现在我们的实验还只能在20mj的层次工作，根据今天的结果，大概产生的可用x-ray（只从某个角度输出）为40000photon/pulse，具体换算成efficiency我还没有算。我们最后的目标当然是要在高能量下工作，因为产生x-ray的过程也是一个non-linear过程，现在还不能预测。

2。实验室温度不稳定，会影响光路，因此影响focus打在金属线上的位置，产生的x-ray减少。另外在早上开机后，能量比较高，下午就逐渐降低了。输出光的稳定性对我们是很重要的，所以这也是一个大问题。

不好意思的说，我以前是做有机的（methane是有机中最简单的分子），还请多多帮助！

atto · 发表于 2004-1-29 01:41:00

[这个贴子最后由atto在 2004/01/29 11:28pm 第 1 次编辑]

150mJ 100fs tunnable from 180nm-1500nm,的确是个很不错的系统,不过我倒很想知道,你们是怎么获得如此高能量的可调谐的输出的? NOPA? OPCPA?
如果使用100mJ的话,我想你们的COMPRESSOR应该在真空中使用的吧?这么高的能量一般都为10Hz.20mJ是比较常见的输出.用金属线产生X-RAY不太熟悉,可能会有很多残渣,方向性也不太好,用气体产生高次谐波比较常见,效率也很低,但光束质量很好.很多研究物理化学的人采用这方法.我不是搞化学的,也许你们的方法有你们的优点?

methane · 发表于 2004-1-29 23:05:00

The AMOLF Terawatt Laser System
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XUV-Physics

The new Amolf laser system is based on the principle of Chirped Pulse Amplification. Short, low-energy pulses are stretched in time before being amplified and then recompressed to their original pulse duration. Stretching the pulses during amplification means that the peak intensity is lowered and enables the pulses to be amplified to high energies without damaging the amplifiers. The wide bandwidth required to support a short pulse (30 nm for a 30 fs pulse) is used to stretch the pulses. The stretcher is designed so that the shorter wavelength components of the pulse must travel along a longer path than the long-wavelength components. The pulse then emerges from the stretcher with the wavelength changing from the front to the back of the pulse:- it is ’’chirped’’.

The start of the laser system is a Ti:Sapphire oscillator pumped by a Millennia laser. This laser produces pulses around 800 nm with a pulse duration of about 15 fs and pulse energies of about 5 nanoJoules. These pulses are stretched to 400 picoseconds in an all-reflective aberration-free stretcher and then amplified in a home-built regenerative amplifier. The regenerative amplifier is operated at 1 kHz and delivers pulses of about 1 milliJoule. The output is amplified to 60 mJ in a 4-pass amplifier, pumped by a Nd:YAG laser operating at 50 Hz. After compression we have 30 mJ in a 50 fs pulse (0.6 Terawatt), capable of producing focused laser intensities in excess of 1018 W/cm2. We plan a further upgrade to the system to maintain a larger bandwidth during amplification, which will mean that the pulses can be compressed to 30 fs. The 950 out of every 1000 pulses from the regenerative amplifier which are not further amplified are compressed in a separate compressor and are available for experiments which require lower pulse energies.

methane · 发表于 2004-1-29 23:07:00

回atto：

为什么不介绍一下attosecond pulses ？

atto · 发表于 2004-1-30 07:14:00

TO METHANE

How do u find that? I didn’’t leave any info...
Anyway,如有兴趣,可以给我发E-MAIL,互相交流交流.

Attosecond pulses还处在初级阶段,还有很多原理性的东西没搞清楚,从产生,测量到应用等各方面.但是的确很PROMISING,如果能实用,搞化学的人肯定也很有兴趣.

liulishuang · 发表于 2004-1-30 19:50:00

偶们天大精仪有几个课题组专门研究飞秒激光的，好想很强的说！

methane · 发表于 2004-1-30 21:08:00

[这个贴子最后由methane在 2004/01/31 11:56am 第 1 次编辑]

to atto:

what is your opinion of the development of as pulses? The decade of my boss was built with ps fs. I am wondering our decade.

清溪流泉 · 发表于 2004-1-30 22:25:00

能不能发表出更详细一点的内容？
关于现在国内的发展情况！

[讨论]关于飞秒激光！！