Aluminum conductivity measurements using a Single-shot terahertz apparatus*

The zero-frequency (DC) electrical conductivity of Warm Dense Matter (WDM) is a critical parameter for the accurate modeling of planetary models [1] and inertial confinement fusion [2]. Here, I will discuss the use of terahertz (THz) spectroscopy integrated into a pump-probe experiment to measure the DC conductivity of WDM. THz pulses are ideal probes of conductivity – THz fields oscillate slowly compared to electron-electron and electron-ion interaction timescales, and THz pulses are short enough to probe transient WDM states created in a lab. The recent development of single-shot THz detection techniques has enabled THz measurements of materials irreversibly driven to extreme conditions [3].  

Using single-shot THz detection, we measure changes in the THz transmission through aluminum thin films irreversibly excited into the WDM regime using intense femtosecond laser pulses. The measured transmission is used to infer the electrical conductivity. By varying the pump pulse energy and arrival time relative to the THz probe, we determine the conductivity under isochoric WDM conditions as well as through the solid-to-liquid transition. The measurements are then compared with theoretical predictions.

[1] D Saumon, G Chabrier, DJ Wagner, and X Xie. Modeling pressure ionization of hydrogen in the context of astrophysics. High-Pressure Research, 16(5-6):331–343, 2000.

 

[2] SX Hu, LA Collins, VN Goncharov, TR Boehly, R Epstein, RL McCrory, S Skupsky, et al. First-principles opacity table of warm dense deuterium for inertial-confinement-fusion applications. Physical Review E, 90(3):033111, 2014.

 

[3] Benjamin Ofori-Okai, Zhijiang Chen, Anthea Weinmann, Lars Seipp, and Siegfried Glenzer. Measuring near-dc conductivity of laser-generated warm dense aluminum using single-shot terahertz spectroscopy. In APS Division of Plasma Physics Meeting Abstracts, volume 2018, pages GP11–017, 2018.