Terahertz time-domain spectroscopy of materials under high pressure in a diamond anvil cell

We present the combination of a broadband terahertz time-domain spectroscopy system (0.1-8 THz), a diamond anvil cell (DAC) capable of generating high pressure conditions of up to 10 GPa, and a cryostat reaching temperatures as low as 10 K. This combination allows us to perform equilibrium and time-resolved THz spectroscopy measurements of a sample while continuously tuning its temperature and pressure conditions. In this study, the procedures and characterizations necessary to carry out such experiments in a tabletop setup are presented. Due to the large modifications of the terahertz beam as it goes through the DAC, standard terahertz time-domain spectroscopy analysis procedures are no longer applicable. New methods to extract the pressure dependent material parameters are presented, both for samples homogeneously filling the DAC sample chamber as well as for bulk samples embedded in pressure media. Different pressure media are tested and evaluated using these new methods, and the obtained material parameters are compared to literature values. Time resolved measurements under pressure are demonstrated using an optical pump-THz probe scheme.