Single-shot spectroscopy of solid-state photoinduced dynamics far from equilibrium

Abstract

Ultrafast single-shot spectroscopy was developed and improved as a method to observe photoinduced dynamics far from equilibrium. The method was then employed to illuminate material dynamics in platinum-halide quasi-one-dimensional chain compounds (PtI) and in the semimetal bismuth. Both material systems exhibit strongly coupled energetic modes; as a result, their study under laser pulse excitation offers the opportunity to explore the same processes that underlie their unique properties. Our measurements have pushed the photoinduced study of these materials to new extremes toward a better understanding of material response and control far from equilibrium. In this thesis, the single-shot method is introduced and analyzed, and measurements on PtI and bismuth are presented and discussed. Collectively, the measurements offer a view into how materials with strong electron-phonon coupling respond to photoexcitation across dimension, timescale, and excitation density. Dimensionality is explored qualitatively between the PtI chain sample and bismuth samples of varying thickness. The time evolution upon laser excitation is monitored from the instantaneous response out to several hundred picoseconds. The photoexcitation itself is varied from weak (corresponding to most published literature on both materials) to very strong (exceeding the thresholds for visualizing dynamics with conventional methods). We describe our results in the context of material dynamics on the microscale and propose future directions. New dynamics were observed in PtI chains that suggest long-lived structural and electronic states under high irradiation. The possibility of collective structural rearrangement with a long lifetime is proposed. In bismuth, high photoexcitation measurements traversed the material's potential energy surface along the coordinate of structural distortion. We report control of the excitation-dependent photoinduced phase by dimensional constraint, as well as ballistic transport effects that govern this interplay. This research enables future advancements on two fronts. The instrumental developments enable visualization of irreversible events for a wider range of materials. The physical insights gained for the materials studied here characterize key processes pertinent to technological applications and off insights that may govern behavior far from equilibrium for broader classes of materials.