基于简并四波混频过程的飞秒脉冲时域对比度提高的研究
文献类型：学位论文
| 作者 | 张素侠 |
| 学位类别 | 硕士 |
| 答辩日期 | 2014 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 刘军 |
| 关键词 | 飞秒脉冲 自衍射 角色散 XPW产生 平凹BaF2晶体 |
| 其他题名 | Temporal Contrast Enhancement of Femotsecond Pulses Based on Degenerate Four-Wave Mixing Processes |
| 中文摘要 | 随着飞秒激光技术与应用的不断发展，对飞秒激光脉冲的要求也越来越高。首先在激光脉冲峰值功率上，由于激光放大技术的发展使得激光脉冲的峰值功率到达太瓦甚至拍瓦量级。拍瓦量级激光脉冲聚焦后峰值功率密度可以达到大于1021W/cm2，在实验室中创造了前所未有的极端物理条件。这种强激光在激光电子加速、实验室天体物理、激光可控核聚变（惯性约束核聚变，ICF）点火研究等强场激光物理的研究中有非常重要的应用。然而，在强激光与物质相互作用时，若预脉冲的聚焦峰值功率达到1011W/cm2时，会在主脉冲到达靶材料之前形成预电离，从而改变激光脉冲与物质相互作用的物理机理或者损坏靶材料。因此，在提高主脉冲峰值功率的同时，为防止预电离的形成，抑制预脉冲和自发辐射本底的强度，提高超短超强激光脉冲的时域对比度已经成为当前超短超强激光研究与应用的重点之一。 本论文的内容主要是采用自衍射效应和利用平凹BaF2晶体的XPW技术提高飞秒激光脉冲时域对比度的研究。 主要研究成果如下： 搭建了利用自衍射（SD）方法来提高飞秒激光脉冲的时域对比度的实验装置。这种SD方法不需要偏振元件来分离产生的SD信号光，可获得更高对比度的激光输出。SD效应还可以平滑光谱，展宽光谱，压缩脉冲宽度，改善光斑质量。 提出并且实验实现了利用直角等腰棱镜来减小SD信号光角色散的新方法。在SD效应实验中通过在一路入射光中加入直角等腰棱镜引入与SD1信号大小相同的预补偿角色散来减小SD信号光的角色散。实验中，当到棱镜表面的入射角为23度，到融石英平片入射夹角在1.26到1.56度之间时，我们将800nm/38fs的飞秒激光产生的SD1信号的角色散减少到无棱镜情况下角色散大小的四分之一。 首次提出利用平凹形状的BaF2晶体产生XPW效应来提高飞秒脉冲对比度。这一平凹结构可以避免以往利用平片BaF2晶体在空气中的成丝现象，可以提高入射光能量，简化光路结构。并且平凹晶体则能利用自身的平凹结构，对入射光束有发散的作用，因此在一定程度上能够抑制入射光束的自聚焦效应，从而可以提高入射光的光强和晶体长度，进而提高XPW的转换效率。初步实验表明，利用平凹BaF2晶体的XPW产生效率要比同等条件下平片的效率高，效率由原来的11.4%提高到现在的13.5%。 参与搭建了基于瞬态光栅效应的集成飞秒脉冲测量装置，在同一装置中实现了自参考光谱干涉和FROG两种方法对800nm/40fs飞秒激光脉冲的脉宽和相位测量。这一装置大大地拓展了飞秒脉冲装置的适用范围。 |
| 英文摘要 | With the development of femtosecond laser technology and application，femtosecond laser pulses must meet more requirements. At First, owning to the great progress in amplification technique, the terawatt, even petawatt femtosecond laser systems have been built up. The peak intensity of the petawatt-class laser pulses after focused has recently reached a level as high as 1022 W/cm2. Such ultrahigh intense laser pulses provide created unprecedented extreme physical conditions in laboratories. This kind of intense laser has very important application in the research of high field laser physics, such as, laser electron acceleration, laboratory astrophysics, laser controlled nuclear fusion (inertial confinement fusion, ICF) Ignition research and so on. In a general experiment of laser–matter interactions, the 1010W/cm2 prepulse or the amplified spontaneous emission(ASE) pedestal with even fewer picoseconds before the main pulse is strong enough to produce preplasma before the main pulse reaches the target, Change the physical mechanism of laser–matter interactions or damage to the target material , then destroys the experimental result. Thus, with the peak intensity of the main pulse increasing, In order to prevent the formation of preplasma, the temporal contrast of ultrahort ultraintese laser pulse has become one of the key points in ultrahort ultraintese laser research and application. The main contents of this dissertation include the study of temporal contrast enhancement of femotsecond pulses based on self-diffraction(SD) process and Cross-Polarized Wave(XPW) generation technology by using a plane concave BaF2 crystal. The main results in this dissertation have been summarized as follows: Set up an experimental device for femtosecond pulses characterization based on Transient-Grating effect, in which both the self-referenced spectral interferometry and the FROG were used to measure pulse width and spectral phase of femtosecond pulses with 40 fs at 800nm center wavelength. The device extended the application range in the measurement of femtosecond pulses. Build an experimental device for temporal contrast enhancement of femotsecond pulses based on SD process. The SD effect does not need to separate the SD signal light with a polarizer. Thus, it is expected to obtain a higher contrast improvement. At the same time, the SD effect can smooth and broad laser spectrum. The pulse duration of the generated SD signals can be shortened, and the beam profile and beam quality can be improved in the process. The angular dispersion of generated SD signal was improved by using a rectangular prism placed on one of the incident beam in the SD process. When the introduced precompensation angle dispersion has same size with the self-diffraction signal, the angular dispersion of self-diffraction signal is obviously reduced. The incident pulse has a center wavelength of 800nm and a pulse width of 38 fs. When the incident angular on the surface of the prism is 23 degrees, the incident angle on the surface of the fused silica is between 1.26 to 1.56 degrees, the angular dispersion of first self-diffraction signal is minimum, which is a quarter of the angular dispersion of that without prism. A plane concave BaF2 crystal is used in the XPW generation process to enhancement temporal contrast of femotsecond pulses for the first time. Filamentation can be avoided in the air by using this BaF2 crystal plate. Then, the experimental setup will be simplified and the incident pulse energy can be increased. At the same time, the plane-concave plate can delay the self-focusing effect of the incident beam, which can increase the conversion efficiency of XPW generation. The first step experiment shows that the conversion efficiency of XPW generation in the experiment is better than that by using a plane BaF2 crystal plate in the same condition, which is improved from 11.4% to 13.5%. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/16858]  |
| 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 | 张素侠. 基于简并四波混频过程的飞秒脉冲时域对比度提高的研究[D]. 中国科学院上海光学精密机械研究所. 2014. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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