Phase-modulated High Harmonic Generation

基于高功率飞秒激光脉冲产生高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中相应的XUV脉冲很容易用于实验，但脉冲操作（如用于泵浦探测实验的分裂和延迟单元）或脉冲对的特定相位控制在XUV中仍然具有挑战性。这就是为什么复杂的光谱技术，如相干（多维）光谱学，到目前为止还没有在XUV波长上进行的原因之一。此外，由于高压源的低XUV光子通量，在气相目标上的实验具有挑战性，因为它可以利用丰富的电子和离子检测选项。在这个项目中，我们将在基于相位调制技术和高谐波锁相检测的相干XUV光谱产生XUV脉冲对方面开辟新的领域。该方法只对红外驱动激光场进行控制，避免了对XUV脉冲的相位和延时控制。该项目旨在证明其技术可行性，阐明其局限性，并进行首次实验表征XUV相位控制特性。实验证明了该方法在不同方向和互补检测技术上的适用性。一方面，对原子和分子光束以及气体目标进行XUV波包干涉测量，揭示激发态的相干动力学。我们将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提高双光子跃迁（RABBITT）重建阿秒拍频实验灵敏度和选择性的新方法，为高阶边带拍频结构的实验开辟新的前景

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