Ultrafast Transient Absorption and Multi-Wave Mixing Spectroscopies in the Extreme Ultraviolet and Soft X-RAY Regimes

Abstract

Unravelling electronic dynamics within atoms and molecules represents a frontier in modern chemistry and biology, offering profound insights into the fundamental mechanisms driving chemical reactions and biological processes. Ultrafast sciences,harnessing the power of cutting-edge spectroscopy, diffraction, and imaging techniques, have emerged as pivotal in capturing these transient events with unprecedented temporal resolution. Advancements in ultrafast laser technology enable researchers to observe and manipulate electronic states within their natural attosecond, femtosecond, and picosecond timescales, thus providing a deeper understanding of the electronic processes that underpin structural changes, reaction pathways, and energy transfer in complex systems. By bridging the gap between theoretical predictions and empirical evidence, ultrafast sciences are revolutionizing our comprehension of the microscopic world, with significant implications for chemistry, biology, and material science. In this dissertation, we lay a theoretical foundation for light-matter interaction, laser-induced transient effects, and pump-probe interactions. We present the recent development in ultrafast laser technology using solid-state lasers such as Ti:Sapphire and Ytterbium-based lasers. We extend to novel spectral broadening and pulse compression techniques such as self-phase modulation in hollow-core fibers and chirped-mirror dispersion compensation. We showcase the application of such novel ultrafast pulses in probing dark state dynamics with femtosecond temporal resolution in a novel three-color wave mixing spectroscopic scheme. The proposed three-color scheme provides additional advantages in accessing excited dark states through background-free emission by exploiting non-commensurate probe IR fields. Finally, we provide technical instrumental details involved in typical pump-probe absorption and photoelectron spectroscopies. Such elegant techniques require a delegate vacuum setup, special EUV and x-ray optics, photon budget and dispersion management.