Full-field characterisation of a novel femtosecond field synthesiser and applications in ultrafast science

该项目关注的是全场，即电场波形，一种新的，高功率，多色飞秒场合成器的特性正在阿托秒实验室（物理系，帝国理工学院）开发。该合成器将能够产生飞秒脉冲，通过锁相频率通道的相干组合对波形进行前所未有的控制，这些频率通道都来自单个激光源。一个关键的要求是充分考虑到供应商的输出，以允许其优化，例如。使用自适应反馈来为特定应用定制波形。持续时间小于20fs的“任意”波形的这种全场表征是极其具有挑战性的。传统的搜索技术，如FROG和SPIDER，不适合于此目的。该项目将探索互补的新方法，包括阿秒条纹，和基于高谐波产生的技术（如。ARIES方法）。必须考虑测量速率，理想情况下应尽可能高，以允许接近波形的实时测量（即接近1kHz）。一旦波形被表征，该项目将准备进入下一阶段的工作，即将波形用于超快科学的新应用。这些可能包括优化高次谐波产生的通量，阿秒x射线脉冲的对比度改善，以及使用离子飞行时间和电子速度图成像来测量电离产物的原子和分子的原理验证实验。

This project is concerned with the full-field, i.e. electric field waveform, characterisation of a novel, high-power, multi-colour femtosecond field synthesiser being developed in the Attosecond Laboratory (Physics Department, Imperial College). The synthesiser will be capable of generating femtosecond pulses with unprecedented control of the waveform through the coherent combination of phase-locked frequency channels all derived from a single laser source. A critical requirement is to fully characterise the synthsesier's output to allow its optimisation eg. using adaptive feedback to tailor the waveform for a particular application. Such full field characterisation of "arbitrary" waveforms of durations less than 20fs is extremely challenging. Conventional metrological techniques, such as FROG and SPIDER are not fit for this purpose. This project will explore complementary new approaches, including attosecond streaking, and techniques based on high harmonic generation (eg. the ARIES method). Consideration must be given to the measurement rate, which ideally should be as high as possible to allow close to real-time measurement of the waveforms (ie close to 1kHz). Once the waveforms are characterised the project will be ready to move to the next phase of work, which is the use of the waveforms for new applications in ultrafast science. These are likely to include optimisation of the flux of high order harmonic generation, the contrast improvement of attosecond x-ray pulses, and proof-of-principle experiments in atoms and molecules using ion time-of-flight and velocity-map imaging of electrons to measure the ionisation products.