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题名	超强超短激光时空质量提升技术研究
作者	吴分翔
文献子类	博士
导师	冷雨欣
关键词	超强超短激光 ultra-intense ultra-short laser 增益红移 gain redshift 脉冲前沿畸变 pulse front distortion 热透镜效应 thermal lens effect
其他题名	Research on the spatio-temporal quality enhancement of ultra-intense and ultra-short laser
英文摘要	啁啾脉冲放大(CPA)技术的发明以及钛宝石生长技术的突破，使得超强超短激光技术得到了迅速发展，其峰值功率已达到了拍瓦量级，脉冲宽度也已实现了数十飞秒量级。目前，多个国家正在竞相研制10拍瓦量级的超强超短激光系统，相应激光脉冲的聚焦强度也有望突破1023W/cm2。如此高的激光脉冲聚焦强度可为众多学科研究创造前所未有的实验手段和极端物理条件，从而推动一系列强场激光物理及相关研究的发展。例如，激光尾波场电子加速、高能质子和离子加速、固体高次谐波等。在大多数强场激光物理及相关研究中，激光脉冲的聚焦强度往往是决定研究成败的重要因素之一。激光脉冲聚焦强度除了取决于激光脉冲的输出能量，还与其时空质量密切相关，包括脉冲光谱、脉冲宽度、脉冲空间光束质量、脉冲前沿、脉冲波前等。因此，超强超短激光时空质量的测量和优化一直是超强超短激光发展的核心问题和研究热点。 本论文瞄准强场激光物理及相关研究对激光脉冲高聚焦强度的需求，围绕实验室已有和在建的超强超短激光系统，对其时空质量的测量和提升技术展开相关研究。研究内容主要包括：研究宽带激光脉冲放大过程中增益窄化和红移现象对输出光谱及近场压缩脉宽的影响，并提出抑制增益红移的新技术方法；研究超强超短激光脉冲前沿畸变对脉冲聚焦特性的影响，并提出新型的测量及补偿脉冲前沿畸变的技术方法；研究超强超短激光系统中热透镜效应对输出脉冲能量及光束质量的影响，并提出抑制热透镜效应的新技术方法。本论文主要取得了以下创新成果和研究进展： 1. 作为主要成员，参与建成峰值功率200太瓦、脉冲宽度27飞秒、重复频率1赫兹的钛宝石飞秒超强超短激光系统，并对其综合性能进行优化。通过发展光束整形、自准直等关键技术，获得了较好的近场光斑质量、能量稳定性、以及光束指向性。该激光系统主要用于驱动电子加速及X射线自由电子激光，目前已驱动产生能散度优于1%、能量达500Mev的加速电子输出，以及波长~30nm、能量接近 100nJ的软X射线输出。 2. 提出并验证了超强超短激光系统中光谱增益红移抑制的新技术，通过钛宝石再生放大器中光谱预整形和级联放大器增益分布的优化，可以有效地抑制高峰值功率钛宝石激光系统中的增益红移效应；理论计算表明该方法可使10拍瓦量级的钛宝石激光器实现65nm半高全宽的放大光谱输出，支持21飞秒傅里叶极限变换脉冲宽度；还进一步研究了大能量钛宝石激光放大器中泵浦光和信号光之间的延时对增益红移的影响。 3. 基于自参考二阶互相关技术，提出了可支持10拍瓦量级超强超短激光脉冲前沿畸变的直接测量新方案，并研究了脉冲前沿畸变对聚焦脉宽的影响。测量结果表明200太瓦钛宝石激光系统输出的80mm直径脉冲所对应的最大脉冲前沿延时为54飞秒，是脉冲宽度27飞秒的两倍，理论模拟表明此脉冲在焦点处的远场脉宽为38飞秒。同时，为了获得更高的聚焦强度，提出了一种简单的脉冲前沿畸变补偿方案。 4. 提出了一种利用具有特定扩束比和发散角的扩束系统来补偿钛宝石超强超短激光放大器中热透镜效应的新方法，此方法可在不额外引入光学元件的基础上对重复频率高能钛宝石多通放大器中的热透镜效应实现有效补偿。实验结果表明，此方法可使我们200太瓦钛宝石激光系统中第二级四通放大器的能量提取效率提升10%，且能够有效地避免热透镜效应所导致的严重波前畸变。此外，该方法还能够有效地降低热透镜效应所引起的激光工作物质损伤的风险。; Thanks to the invention of chirp pulse amplification (CPA) technology and the breakthrough in the development of Ti:sapphire crystal, the ultra-intense ultra-short laser technology has been rapid developed. The laser peak power has been up to PW (petawatt) level, and the pulse duration has also reached dozens of fs (femtoseconds). At present, many countries are competing for the development of 10 PW level laser systems, and the focus intensity of laser pulses is also expected to exceed 1023W/cm2. Such focus intensity of laser pulses can create unprecedented experimental means and extreme physical conditions for many disciplinary researches, and promote the development of a series of high-field laser physics and related researches. Such as the laser wavefield electron acceleration, high energy protons and ions acceleration, solid high-order harmonic. The laser focus intensity generally plays a decisive role in the success of the vast majority of high-field laser physics and related researches. The laser focus intensity is not only depend on pulse energy, but also closely related to its spatio-temporal quality, including pulse spectrum, pulse duration, pulse spatial beam quality, pulse front, pulse wavefront, and so on. Therefore, the spatio-temporal quality measurement and optimization of ultra-intense ultra-short laser is always the core problem and research hotspot in the ultra-intense ultra-short laser area. This dissertation is aimed at the requirement of high focal intensity of laser for high-fiels laser physics and related researches, and focusing on the spatio-temporal quality measurement and enhancement technique researches of ultra-intense ultra- short laser systems, existing and under construction in our laboratory. The main content include: investigating the effect of gain narrowing and redshift during the progress of broadband laser pulser amplification on the amplified output pulse spectrum and near-field compression pulse duration, and proposing a new technique for the gain redshift suppression; investigating the effect of pulse front distortion on the focusing characteristics of ultra-intense ultra-short laser, and proposing novel schemes of measurement and compensation for pulse front distortion; investigating the effect of thermal lens on the amplified output pulse energy and beam quality in ultra-intense ultra-short laser systems, and proposing a new method for the thermal lens suppression. The major innovation achievements and research progresses are listed as below. 1. As a principal member, I participated in the construction of the Ti:sapphire fs ultra-intense ultra-short laser system, with 200TW peak power, 27fs pulse duration, 1Hz repetition rate, and its comprehensive performance is optimized. By utilizating key technique, such as laser beam shaping, auto-collimation etc, the near-field beam profile, energy stability, and beam directivity are good. The laser system is mainly used to drive the laser wakefield electron acceleration and X-ray free electron laser experiments. Now, we have experimental realized 500Mev energy electron output with 1% energy spread, and 100nJ energy soft X-ray output at the centra wavelength of 30nm. 2. We proposed and verified a new technique for the gain redshift suppression in ultra-intense ultra-short laser systems. By the optimization of spectral pre-shaping in regenerative amplifier and gain distribution of cascaded multi-pass amplifiers, the gain redshift in high-peak-power Ti:sapphire lasers can be efficiently suppressed. Moreover, the result of theoretical simulation indicated that by utilizing this method, the future 10PW Ti:sapphire laser can realize 65nm bandwidth at FWHM (full width at half maximum) spectral output, which can support 21fs Fourier-transform limited pulse duration. Apart from this, the influence on gain redshift induced by different time delay between seed and pump pulses in high-energy Ti:sapphire amplifiers was also inveatigated. 3. Based on the self-reference and second-order cross-correlation technologies, we innovatively proposed a direct pulse front distortion measurement scheme, which can applied to the 10PW-level ultra-intense ultra-short laser systems, and the effect on pulse duration at the focus induced by pulse front distortion was also investigated. The measurement scheme was applied in our 200TW Ti:sapphire laser system, and the beam size of output pulse is 80 mm in diameter. The measured result indicated that the maximal time delay between different parts of pulse front is 54.4fs, twice the 27fs pulse duration. Moreover, the pulse duration at the focus is theoretically simulated to be 38 fs in this case. In addition, in order to obtain higher intensity laser output, we proposed a simplified compensation scheme for pulse front distortion. 4. Without introducing any extra optics, we proposed a new method, utilizing a particularly beam expander with specific expanding ratio and beam divergence, to suppress the thermal lens effect in repetition-rate high-energy Ti:sapphire amplifiers. The experimental result indicated that, by this method the enhancement of energy extraction efficiency can reach about 10% for the second four-pass amplifier in our 200TW Ti:sapphire laser system, and the thermal lens induced significant wavefront aberration and laser work material damage can also be avoided.
学科主题	光学
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/31114]
专题	中国科学院上海光学精密机械研究所
作者单位	中国科学院上海光学精密机械研究所
推荐引用方式 GB/T 7714	吴分翔. 超强超短激光时空质量提升技术研究[D].

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