中红外波段强场中的电子超快动力学相干操控及其应用研究
文献类型：学位论文
| 作者 | 姚金平 |
| 学位类别 | 博士 |
| 答辩日期 | 2011 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 程亚 |
| 关键词 | 高次谐波 阿秒脉冲 双色场 水窗 电子波包扩散 |
| 其他题名 | Coherent control of ultrafast electron dynamics by mid-infrared femtosecond laser pulses and its application |
| 中文摘要 | 高次谐波产生在建立时空高度相干、波长连续可调、飞秒乃至阿秒量级的台式化XUV和X射线源方面有着极其诱人的前景。无论是作为X射线激光器或者自由电子激光器的种子源，还是直接用于探测微观超快动力学过程，高能、高亮度、时空高度相干的谐波光子输出和阿秒脉冲辐射一直是人们追求的目标。基于钛宝石激光系统输出的近红外波段（~800nm）、高能量、多光周期甚至少光周期的飞秒激光脉冲，高次谐波辐射已经从最初的XUV波段深入到“水窗”波段（284-543eV）甚至光子能量高达KeV的X射线波段。结合泵浦脉冲整形方案，高次谐波合成的阿秒脉冲宽度越来越短，目前，实验上已经成功地产生了80as的单个脉冲输出，为研究电子的超快动力学提供了强有力的工具。 近年来，毫焦耳量级、多光周期甚至少光周期量级的可调谐中红外(1μm<λ<5μm)新波段激光光源的出现与迅速发展，开辟了强场物理领域中迄今仍很少探索过的参量空间，为开拓强场相互作用新物理、新效应及新应用提供了新机遇。基于中红外新波段的高次谐波辐射由于在产生高能、高亮度谐波光子、合成更短的阿秒脉冲方面的潜在优势，已经成为国际研究的热点问题。 本论文瞄准中红外波段高次谐波产生的国际前沿问题，利用可调谐中红外波段的超强超短激光平台，在实验上研究了高能光子产生以及电子波包动力学的操控与表征，在理论上研究了利用波形控制光场，一方面可以在多光周期光场中产生单个阿秒脉冲，另一方面，可以在高次谐波产生过程中形成窄带、可调谐XUV辐射。主要工作和创新性成果如下： 1. 首次提出通过优化双色场偏振面夹角构造特定波形可以在亚光周期内实现电子波包动力学的有效控制，使得在多光周期光场驱动条件下周期性发生的谐波辐射减小到一次，从而在频域上产频谱带宽高达180eV的超连续辐射，在时域上合成~73as的单个阿秒脉冲。 2. 提出线偏振激光场与椭圆偏振激光场的组合方案。在椭圆偏振激光场的短轴叠加一个长波长、多光周期的线偏振激光场，不仅可以在多光周期泵浦条件下获得近傅里叶变化极限的亚100as的单个脉冲输出，而且可以人为地选择单条量子轨道。 3. 首次在理论上预言了，通过优化垂直偏振双色场的波长比、相对时间延时、强度比等参数，可以实现电子波包动力学的阿秒控制，从而打破高次谐波谱典型的“平台”分布，将高次谐波辐射限定在很窄的频谱范围内。通过调节激光参数，可以在高次谐波产生过程中直接建立窄带、可调谐的XUV辐射。 4. 首次利用高重复频率（1kHz）中红外波段飞秒激光驱动光场，在氩气中获得了高达190eV的谐波输出。激光系统升级以后，利用1.6mJ，1500nm激光脉冲在氖气中成功将高次谐波截至区能量推进到“水窗”波段，并系统研究了气压、焦点位置、聚焦几何条件等参数对高次谐波产率以及空间发散性的影响，为实现台式化、高重复频率、高亮度的“水窗”波段超快光源及其应用奠定了基础。 5. 首次利用中红外激光脉冲观测到高次谐波频谱的干涉图样，通过分析表明这是多条量子轨道干涉的结果。 6. 基于可调谐的中红外光源，测量不同波长下谐波产率和激光椭圆偏振度的关系，研究了谐波对椭偏率容忍度随激光波长的变化，并由此反推出电子波包扩散速度和电子波包的大小。 |
| 英文摘要 | High-order harmonic generation (HHG) provides a potential way for generating coherent, wavelength-tunable, ultrafast, tabletop XUV and X-ray sources. As seed pulses of X-ray laser and free electron laser as well as the tool to probing ultrafast dynamic processes, HHG with high photon energy, high brightness and high coherence has attracted intensive interests. By use of the near-infrared (~800nm), millijoule, multi-cycle even few-cycle femtoseond laser pulses generated from Ti: sapphire laser system, the cutoff energy of HHG has been extended to “water window” (284-543eV) even X-ray regime above KeV. Based on the technique of pump pulse shaping, one has generated shorter and shorter attosecond pulses. Currently, ~80 as isolated pulses have been generated by a 3.3 fs, carrier-envelope phase (CEP) stabilized laser field, which provides a potential tool for investigating ultrafast dynamics of electrons. In recent years, rapid advancement of optical parameter amplifier technology enables us to create millijoule, wavelength-tunable, multi-cycle even few-cycle, mid-infrared laser pulses, which providing new chances for exploring a lot of new effects and phenomenon in the mid-infrared regime. Currently, HHG driven by mid-infrared laser pulses has become one of the hottest research topics in strong field laser physics. The reason is that, the use of the longer laser wavelength can sufficiently extend cutoff energy of high-order harmonics under the condition of optimized phase matching, proving a potential way for obtaining high-photon-energy, high-brightness harmonic emission. Furthermore, the use of the longer laser wavelength can effectively reduce the intrinsic chirp during HHG, leading to the generation of the shorter attosecond pulses. In this dissertation, we focus on experimental investigation on HHG, coherent control and measurement of electron wavepacket dynamics with mid-infrared, wavelength-tunable driving laser field and theoretical investigation on the generation of isolated attosecond pulses in the multi-cycle regime and the creation of narrow-bandwidth, wavelength-tunable coherent XUV sources based on waveform-controlled techniques. The main results and achievements are summarized as follows. 1. By optimizing the angle of the polarization planes of 25 fs, 800 nm laser pulses and 43 fs, 1400 nm laser pulses to construct pump pulses with a specific waveform, HHG process periodically occurring in a multi-cycle laser field is virtually reduced to only once, resulting in that supercontinuum radiation is dramatically broadened to 180 eV. Such broad supercontinuum is sufficient to support an isolated attosecond pulse shorter than 100 as even without any phase compensation. 2. By superimposing a 1400 nm, ~43 fs linearly polarized laser field in the minor axis direction of an 800 nm, 20 fs elliptically polarized laser field, an isolated, shorter than 100 as (close to Fourier-transform-limited) attosecond pulses can be generated, but also the single quantum trajectory can be selected. 3. High-order harmonic spectrum with a narrow bandwidth of ~4 eV is obtained by constructing a specific waveform using the orthogonally polarized two-color laser field that only allows the electron born at a unique time to be driven back to the parent ion. From the well-known simple-man picture, the kinetic energy of the returning electron will be effectively confined to a narrow region which is determined by the quantum diffusion of electron wavepacket. Furthermore, the center wavelength of the narrow-bandwidth XUV radiation can be continually tuned in a broad spectral range by varying intensity of pump pulses. 4. With mid-infrared femtosecond laser pulses, the maximum photon energy of HHG in argon is up to 190 eV. After the laser system is updated, HHG in neon driven by 1500 nm, 1.6 mJ laser pulses is successfully pushed into “water window” region. The influence of experimental parameters such as gas pressure, focal position, focusing geometry on the yield and spatial characteristics of harmonics around “water window” is systematically studied, which paves the way to creation of tabletop, high-brightness X-ray sources in the “water window” region and its application. 5. Fine interference fringe has been observed in the high harmonic spectrum driven by mid-infrared femtosecond laser pulses, which is proved to be the result of the interference between high harmonics from quantum trajectories. 6. By wavelength scaling of elliptical-polarization dependence of HHG driven by mid-infrared tunable laser pulses, spreading rate and recolliding diameter of electron wavepacket can be well estimated. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15675]  |
| 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 | 姚金平. 中红外波段强场中的电子超快动力学相干操控及其应用研究[D]. 中国科学院上海光学精密机械研究所. 2011. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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