Experimental determination of the electrical conductivity of compressed matter using ultrafast terahertz radiation*

While the electrical conductivity is a vital parameter for describing HED matter, the direct measurement of conductivities in laser-driven compression experiments is

challenging. Modelling processes such as planetary dynamos and the stability of inertial confinement fusion implosion requires detailed knowledge of the DC-conductivity and

the equation of state of these exotic states of matter. It has recently been demonstrated that terahertz pulses are suitable to measure the electrical conductivity of warm dense

matter and dense plasmas, as THz fields are sufficiently slowly varying that they behave like DC fields on the timescale of electron-electron and electron-ion interactions, and

hence probe DC-like responses. Here, we present recent experimental results combining long-pulse and short pulse laser systems to measure the THz reflectivity of

shock compressed matter. By taking advantage of the different Hugoniots of polystyrene and polyethylene terpthalate, our measurements span different regions of phase space

including above the carbon melting line, regions where diamonds are expected to form, and regions where hydrogen is predicted to undergo an insulator-to-metal phase

transition. From our data we extract optical constants of the compressed plastics including the refractive index and provide estimates of the electrical conductivity.