| 题名 | 基于时空特性受控强场超快激光的极端非线性光学研究 |
| 作者 | 曾斌 |
| 学位类别 | 博士 |
| 答辩日期 | 2012 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 徐至展 ; 程亚 |
| 关键词 | 高次谐波 阿秒脉冲 飞秒激光成丝 远程探测 |
| 其他题名 | Investigations of Extreme Nonlinear Light-Matter Interaction Based on Spatio-temporally Controlled Ultrafast Laser Pulses |
| 中文摘要 | 强场超快激光与物质的相互作用，突破了传统的（即符合微扰理论的）非线性光学的框架，开辟了以非微扰相互作用为特征的极端非线性光学这一全新学科领域。极端非线性光学中，光与物质（典型如原子、分子、凝聚态等）间的相互作用均发生在电离阈值附近的光强条件下（在此基础上如进一步提高光强，物质体系将在强光场中被迅速电离破坏，形成等离子体）。在这一特殊的光强条件下，光与物质，特别是原子、分子的相互作用导致了一系列崭新现象的发生，包括高次谐波产生、非序列双电离、超快非线性成丝等。因此，近二十年来，极端非线性光学已成为当代物理学，特别是非线性光学领域中的研究前沿。 由于在上述的极端非线性相互作用中，物质对象对光场的响应尤为敏感且具有非微扰、高度非线性等特性，因此控制光场的时空特性显得尤为重要。当前，利用时空特性精密操控的强场超快激光进行强场物理的研究是该领域的前沿热点，并已经产生了一批重要的新原理、新技术和新发现，如产生脉宽仅为80阿秒的单阿秒脉冲等。 本论文工作瞄准时空特性受控强场超快激光作用下的极端非线性光学这一物理前沿领域，重点发展并利用新的光场操控手段，着重解决高能量强场激光脉冲驱动的高次谐波与阿秒脉冲产生，以及非线性成丝中的关键科学问题，如利用单色场多周期长脉冲激光直接驱动产生高强度单阿秒脉冲、突破飞秒激光成丝中的“强度钳制”效应等。特别是本论文首次将时-空聚焦这一全新的光场操控技术用于超快非线性成丝的研究，在大能量短脉冲条件下（10 mJ, ~50 fs）有效提升了光丝中的钳制光强，并进而成功地提高了飞秒远程探测的灵敏度。我们预期，进一步的后续研究还将推动这一新技术在强场物理的其它重要研究分支中获得重要应用。 本论文的主要工作内容和创新性成果如下： 1. 首次采用高能量多周期激光脉冲与物质相互作用过程中诸多非线性效应诱导的泵浦脉冲时空整形，直接产生高亮度的光子能量从35eV到50eV的极紫外超连续谱。该连续谱可支持的最短傅里叶变换极限脉宽为271阿秒，通过对经过气体盒子的激光脉冲进行时间空间特性的分析，表明传输效应在极紫外超连续谱产生中起重要作用。该工作与传统产生单阿秒脉冲方案相比，实验装置简单，对激光器系统要求低，为产生高亮度单阿秒脉冲光源开辟了新方法。 2. 首次将时间-空间聚焦技术应用于飞秒激光成丝中，通过改变入射激光脉冲的时空特性，不仅有效地控制了光丝的形态，将光丝的长度缩短了约25倍，而且进一步提高了飞秒激光成丝中的钳制光强，与传统聚焦方案相比，时间-空间聚焦技术可将光丝内的峰值光强提高30%。 3. 首次成功地将飞秒激光的时空-空间聚焦技术运用于远程成丝诱导击穿探测中，在 远处的铁材质固体靶上成功观测到荧光信号的五倍增强，为提高远程探测的灵敏度和信息量提供了有效途径。 4. 采用单原子模型对双色激光场产生高次谐波进行数值模拟，从理论上验证了通过对高次谐波产生过程中电子隧穿电离和加速行为的精确控制，从而影响高次谐波的量子轨道，最终利用脉宽仅为3.5飞秒的近红外激光及其频率失谐的倍频场构成的双色场，实现光子能量从80eV到100eV可调的连续谱输出，这种中心波长可调的单阿秒脉冲在阿秒泵浦-探测技术中有极大应用价值。 |
| 英文摘要 | Ultrafast laser-matter interactions, which break up the theoretical framework of traditional nonlinear optics, i. e. the perturbative theory, open a new era of extreme nonlinear optics in non-perturbative regime. In extreme nonlinear optics, the intensity of the laser field is approaching the ionization threshold of the media (such as atoms, molecules, condensed matter, etc.) under exposure. Namely, for higher intensities, the interacting media will be fully ionized by the laser field and become plasma. Under such conditions, the interactions of ultrafast laser with the media, especially atoms and molecules, lead in many novel and interesting phenomena, e. g., high-order harmonic generation, non-sequential double ionization and femtosecond filamentation. Above all, extreme nonlinear optics has become a frontier research field in modern physics, especially in the field of nonlinear optics. In extreme nonlinear optics, the response of the media to the light fields is non-perturbative, highly nonlinear, and thus very sensitive to the laser field. For this reason, it is of great significance to control the spatial and temporal characteristics of the ultrafast laser. Nowadays, using spatial and temporal manipulated ultrafast laser field to investigate the high field laser physics has become a hot research topic in nonlinear optics. Many new theories, techniques and discoveries have been achieved. As an example, isolated ~80 attosecond pulses have been observed. Aiming to study the extreme nonlinear optics with spatio-temporally controlled ultrafast laser pulses, we develop new techniques to control the laser fields for studying the high-order harmonic generation and attosecond pulses with high energy femtosecond laser pulses, for solving some key issues in femtosecond filamentation. The major results we achieved are generation of intense extreme ultra-violet supercontinua with a high-energy multi-cycle femtosecond laser and breaking the intensity limit originating from the well-known “intensity clamping” effect in femtosecond filamentation. Most importantly, for the first time to our knowledge, we apply a novel spatio-temporal focusing technique in the study of strong field laser physics, i. e. femtosecond filamentation. Thus, the peak intensity in the filament core, which is inherently limited by the intensity clamping effect, and the femtosecond remote sensing detection sensitivity have been enhanced. We expect that this new technique can be also useful for other applications in strong field laser physics. The main results and innovations are listed as follows: 1. We demonstrate the generation of intense extreme-ultraviolet supercontinuum with photon energies spanning from 35 eV to 50 eV, that supports an isolated attosecond pulse with a duration of ~271 as, with a high-power multi-cycle femtosecond laser. The dramatic change in spectral and temporal properties of the driver pulses after passing through the gas cell indicates that propagation effects play a significant role in promoting the generation of the EUV supercontinuum. This new technique will greatly simplify the attosecond pulse generation and make a more efficient use of the driver pulses. 2. For the first time, we demonstrate that the peak intensity in the filament core, which is inherently limited by the intensity clamping effect, is enhanced by 30% with spatio-temporal focusing technique. In addition, the filament length obtained by spatio-temporally focused femtosecond laser pulses is ∼25 times shorter than that obtained by a conventional focusing scheme, resulting in improved high spatial resolution. 3. We show the spatio-temporally focusing technique can be applied in remote filament-induced breakdown spectroscopy to improve the detection sensitivity and the signal-to-noise ratio. Fluorescence intensity enhanced by up to five times on Fe sample at 22 m away has been observed. 4. Numerical simulation on high order harmonics generation by two-color field based on single-atom model. We theoretically demonstrate that, the processes of electron tunneling in the high-order harmonic generation process and subsequent positive-energy wavepacket propagation until re-collision can be controlled with the unprecedented precision of about 10 attoseconds by two-color field. Tunable extreme ultraviolet continua between 80 and 100 eV can be generated, which will tremendously broaden the scope of attosecond pump–probe spectroscopy. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15684]  |
| 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 | 曾斌. 基于时空特性受控强场超快激光的极端非线性光学研究[D]. 中国科学院上海光学精密机械研究所. 2012. |
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