UC Berkeley

Nonlinear spectroscopic techniques with attosecond extreme ultraviolet (XUV) pulses produced by high harmonic generation promise to enable the study of ultrafast processes driven by electronic dynamics. Although nonlinear spectroscopies are regularly utilized to probe chemical dynamics driven by nuclear motion, the extension of these techniques to electronic dynamics has been limited by the low flux of attosecond light sources. In this dissertation, nonlinear techniques that incorporate subfemtosecond XUV pulses and few-cycle near infrared (NIR) pulses generate transient higher-order signals from electronic states in gas-phase and solid-state samples. Manipulation of the pulse sequence, wavevector, and spectrum permits selective measurements of dynamic processes with exceptional temporal and spectral resolution. This dissertation details the development and application of attosecond nonlinear spectroscopies. Attosecond transient absorption experiments at the iodine N4,5 edge of ICl demonstrate that the molecular environment dramatically impacts core-excited state lifetimes. To probe these electron correlation-driven dynamics more selectively, an attosecond wave-mixing spectroscopy has been developed. Capitalizing on phase matching to isolate higher order signals, wave-mixing experiments on the 1snp Rydberg and light-induced states in helium reveal few-femtosecond delays in higher order signal generation due to the accumulation of a phase grating. Further experiments on this system show that wave-mixing signals from light-induced states can be amplified using self-heterodyne detection schemes. Moreover, these attosecond wave-mixing techniques are employed to measure the lifetimes of states that decay via electron correlation. Despite pronounced quantum beating, lifetimes obtained for the (2P1/2)nd autoionizing states of krypton compare favorably with linewidth measurements. In solid-state NaCl, attosecond wave-mixing techniques uncover several additional core-excitons that underlie the absorption features of Na+ L2,3 edge, and report ultrafast bright and dark state dynamics suggestive of the complex environment. Designed to differentiate distinct contributions to higher order emission signals, an XUV multidimensional spectroscopy based on a pulse shaping apparatus effectively eliminates quantum beat signatures in a proof of principle experiment in argon.

These results illustrate the potential of attosecond nonlinear spectroscopies to elucidate dynamics driven by electron correlation in diverse systems with unprecedented selectivity. Future work will translate these nonlinear techniques to the chemically-significant carbon K-edge, where they will provide insight into the electronic dynamics foundational to chemical reactions.