Shock compression of pre-compressed hydrogen

Shock compression experiments on hydrogen samples are usually carried out with cryogenic initial conditions. A new sample preparation technique for laser driven shock compression employs room-temperature fluid samples confined within a pair of diamond anvil flats at high static pressures. We performed shock compression experiments on hydrogen samples pre-compressed to ∼ 1 GPa using the Vulcan laser at Rutherford-Appleton Laboratory to drive ∼ 40 GPa shocks into these samples. The pre-compressed initial state allows us to probe a region of the phase diagram at significantly higher densities compared to cryogenic samples. We diagnosed the shock front using a pair of velocity interferometers operating at probe wavelengths 1064 nm and 532 nm simultaneously. The experiments reveal new information on the nature of the insulator-metal transition in the compressed fluid phase.