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UBC Theses and Dissertations

Optical properties of ultrafast laser heater solid Ao, Tommy

Abstract

The regime of Warm Dense Matter (WDM) has emerged as an interdisciplinary field which has drawn broad interest from researchers in plasma physics, condensed matter physics, high pressure science, astrophysics, inertial confinement fusion, as well as material science under extreme conditions. Warm dense matter represents complex states at the convergence of condensed matter physics and plasma physics where neither conventional theoretical descriptions are valid. However, single-state experimental data for the direct testing of new theoretical models within this regime has been difficult to come by. To examine the WDM state, the optical properties of ultrafast laser heated solids were studied. Experiments were performed utilizing a femtosecond laser pump-probe technique to create and examine single-states of WDM. The isochoric heating of freestanding, ultrathin (30 nm), gold foils by a femtosecond pump laser produced uniform, solid-density states of energy densities from 0.25 to 20 MJ/kg. The AC conductivity of such states was determined from reflectivity and transmission measurements of a femtosecond probe as a direct benchmark for transport theory. In addition, observation of the time history of the probe reflectivity and transmission led to the discovery of a quasi-steady-state behavior of the heated sample that suggests the existence of a metastable, disordered phase prior to the disassembly of the solid. To further examine the dynamics of ultrafast laser heated solids, Frequency Domain Interferometry was used to provide an independent observation.

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