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题名	超短脉冲强激光与透明固体及气体介质相互作用的若干问题研究
作者	李跃勋
学位类别	博士
答辩日期	2009
授予单位	中国科学院上海光学精密机械研究所
导师	李儒新
关键词	飞秒脉冲激光，非线性传输，成丝，锥形辐射，非绝热分子取向，斜率法则
其他题名	Study on some problems relevant to the interaction of Ultra-short Intense Laser Pulse with transparent solid and gaseous materials
中文摘要	近年来，随着飞秒激光技术的发展，超快高强度飞秒脉冲激光在透明光学介质中的传输和相互作用的研究已经成为国际上激光物理领域的研究热点。当飞秒脉冲激光在透明介质（固体，液体和气体）中传播时，高强度的脉冲激光会引起介质的高阶非线性效应，导致介质折射率的改变，从而极大地影响激光束在透明介质中的传输特性，并且产生了一些非常有趣的非线性光学现象（成丝，锥形辐射和超连续谱的产生等）。另外，除了要考虑介质的各种线性和非线性效应对激光束特性的影响之外，值得考虑的还有脉冲激光在介质中传播时其对介质的作用。 本论文针对高强度飞秒脉冲激光与固体及气体介质的相互作用的若干问题开展了一系列实验和理论的研究工作。主要的工作和成果如下： 1．在实验上观察了入射激光在不同脉宽和带宽下的锥形辐射发散角，结果表明：锥形辐射发散角将随着入射脉冲激光带宽的变化而变化。而对于相同带宽不同脉宽的入射脉冲激光，当锥形辐射光谱频移量较小时，锥形辐射发散角相同。而随着锥形辐射光谱频移量的增大，脉宽不同（即使带宽相同）的脉冲激光产生的锥形辐射发散角将不同。我们根据锥形辐射的X波模型拟合了我们的实验结果，拟合曲线与实验结果符合得很好。这个现象表明了：入射脉冲激光的带宽能有效地控制激光在透明固体介质中的群速度。 2. 在实验上初步研究了脉冲激光在熔石英介质中各种成丝及相应的锥形辐射的空间分布模式。结果表明：相同带宽（不同脉宽）的脉冲激光产生相似的锥形辐射模式需要的阈值功率是一样的。此外，对于某一种锥形辐射模式而言，入射激光带宽愈宽，要产生该种模式的锥形辐射需要的阈值功率更高。 3. 在实验上首次发现了低入射功率下锥形辐射光谱中的红移成分。在实验上，锥形辐射光谱成分大多是蓝移的成分，尤其是入射脉冲激光的中心波长处于近红外波段时。而我们在实验中用中心波长为800nm的脉冲激光作用于BK7玻璃，结果发现在低入射功率下，有红移的锥形辐射出现。且在一定的入射功率范围之内，随着激光入射功率的不断增大，红移锥形辐射环的亮度也会逐渐的增强。但只要入射脉冲激光能量增加到使蓝移的锥形辐射成分出现，那么，红移的锥形辐射成分将逐渐淡没。 4. 在理论上模拟了用飞秒脉冲激光产生分子转动波包，然后用第二束脉冲激光来实现对该转动波包的主动控制。我们在理论上提出了一套新颖的方案—“斜率法则”来实现对分子转动波包的相干性的主动控制。通过“斜率法则”，我们可以通过选取特定的延时实现分子转动波包的关闭（分子取向度极大的降低）或打开（分子取向度极大的提高）。另外，还可以将其应用到多脉冲分子取向中。
英文摘要	Recently, the studies on propagation characteristics and the interaction of femtosecond laser pulses in transparent media have been a hot topic in the laser physics field. When a femtosecond laser pulse is propagating in transparent media (including solid，liquid and gas), it can induce high-order nonlinear effects, which can change the refractive index of the media. These effects will influence the propagation property of the laser pulse greatly and lead to some interesting nonlinear optical phenomena (such as filamentation, conical emission and the generation of supercontinuum). When a femtosecond laser pulse is propagating in transparent media, it is worth considering that the action of the ultrashort laser pulse on the material, in addition to the effect of linear and nonlinear on the characteristics of laser pulse. In this thesis, we carried out a series of experimental and theoretical investigations relevant to some problems of the interaction of intense femtosecond laser pulses with solid and gas materials. Main work and innovative points of this thesis are as follows: 1. Conical emission (CE) in fused silica has been investigated experimentally by using laser pulses with different pulse durations and spectral bandwidths. The results show that the overall CE curve will shift as the spectral bandwidth of pump laser pulse changes. But for the pump laser pulses with the same spectral bandwidth and different pulse duration, the CE angles are same at the spectral region close to the pump wavelength while they are different at the spectral region far away from the pump wavelength. We have also fitted the measured CE angles with the X-wave model. The calculated curves and the measured CE curves match reasonably well. The results indicate that the group velocity of the filament pulse can be controlled by varying the spectral bandwidth of the action laser. 2. Different filaments and the corresponding conical emission (CE) patterns are preliminary investigated experimentally. The results show that the critical powers for similar CE patterns are nearly the same for the laser pulses with the same spectral bandwidth. Besides, as far as a certain CE pattern is concerned, the wider the spectral bandwidth of pump laser pulse is, the higher the critical power is. 3. The Red-shift conical emission (CE) is observed experimentally for the first time. The spectral components of CE are usually located at the blue-shift side, especially when the centered wavelength of laser pulses is at infrared. However, we observed the red-shift CE in BK7 using a relatively low power femtosecond laser pulse (with the wavelength centered at 800 nm) propagating. Besides, with an increasing laser power the red-shift CE becomes brighter. Whereas, the red-shift CE ring disappears when the laser power is high enough for the blue-shift CE to occur. 4. The rotational wave packet of linear molecules excited non-adiabatically by a femtosecond laser pulse is controlled actively using the second laser pulse. We propose a novel strategy, ‘the rule of slope’，to determine the optimal time delays between the two laser pulses to modify the coherence of the molecular rotational wave packet, by which the molecular alignment generated by the first pulse is suppressed or enhanced by selecting the respective time delays. This control scheme can be applied to the molecular alignment using multi-pulse laser field.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/15274]
专题	上海光学精密机械研究所_学位论文
推荐引用方式 GB/T 7714	李跃勋. 超短脉冲强激光与透明固体及气体介质相互作用的若干问题研究[D]. 中国科学院上海光学精密机械研究所. 2009.

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