Phase-modulated High Harmonic Generation

基于高功率飞秒激光脉冲产生高次谐波的极紫外光源已成为原子分子物理和阿秒科学新方向的有利工具。虽然从HHG相应的XUV脉冲是很容易获得的实验，脉冲操纵，如分裂和延迟泵探测实验，或特定的相位控制脉冲对的单位仍然具有挑战性的XUV。这就是为什么复杂的光谱技术，如相干（多维）光谱迄今尚未在XUV波长进行的原因之一。此外，气相目标的实验，可以利用丰富的选择，在电子和离子检测，是具有挑战性的，因为低XUV光子通量的高次谐波源。在这个项目中，我们将在基于相位调制技术和高次谐波锁定检测的相干XUV光谱学中产生XUV脉冲对方面取得新的进展。在该方法中，仅操纵红外驱动激光场，避免了作用于XUV脉冲的任何相位和延迟控制。该项目旨在证明其技术可行性，阐明其局限性，并进行表征XUV相位控制特性的首次实验。实验证明，在不同的方向和使用互补检测技术的适用性。一方面，将对原子和分子束以及气体目标进行XUV波包干涉，揭示激发态的相干动力学。我们将同时使用光电子能谱和瞬态吸收作为XUV时间分辨实验中最常用的检测技术。另一方面，相位调制技术将作为一种新的方法，提高双光子跃迁重建阿秒拍频（RABBITT）实验的灵敏度和选择性，为更高阶边带拍频结构的实验开辟前景

Extreme ultraviolet (XUV) light sources based on high harmonic generation (HHG) from high-power femtosecond laser pulses have become profitable tools for new directions in atomic and molecular physics, and attosecond science. Although from HHG corresponding XUV pulses are readily available for experiments, pulse manipulation such as split-and-delay units for pump-probe experiments, or specific phase-control of pulse pairs remain challenging in the XUV. This is one reason why sophisticated spectroscopic techniques such as coherent (multidimensional) spectroscopy have not been performed so far at XUV wavelengths. Moreover, experiments on gas-phase targets which can exploit rich options in electron and ion detection, are challenging because of the low XUV photon flux of HHG sources. In this project we will break new grounds in generating XUV pulse pairs for coherent XUV spectroscopy based on a phase modulation technique and higher harmonic lock-in detection. In this approach only the infrared driving laser field is manipulated avoiding any phase and delay control acting on the XUV pulses. The project aims at demonstrating its technical feasibility, elucidating its limitations and performing first experiments characterizing XUV phase control properties. Experiments are proposed to proof the applicability in different directions and using complementary detection techniques. On the one hand, XUV wave packet interferometry on atomic and molecular beams as well as gas targets will be performed revealing coherent dynamics of excited states. We will use both photoelectron spectroscopy as well as transient absorption as the most commonly used detection techniques in XUV time-resolved experiments. On the other hand, the phase modulation technique will be used as a new approach improving sensitivity and selectivity in experiments for the reconstruction of attosecond beating by two-photon transitions (RABBITT), opening prospective experiments on higher order sideband beat structures