Dielectric function and electrical resistivity of liquid carbon determined by femtosecond spectroscopy

Femtosecond pump-probe reflectance of graphite and diamond targets following intense laser irradiation is used to measure the optical properties of the pressurized liquid carbon phase while it retains an optically sharp surface before expanding hydrodynamically as a hot plasma. These measurements allow the historically elusive liquid phase of carbon to be characterized optically for the first time. A Drude dielectric model of the reflectance spectrum 1 ps after excitation just above the melting threshold reveals a poorly conducting liquid metal with a dc resistivity 625±75 · cm. The optically determined resistivity decreases with increasing sample excitation. The initial stages of hydrodynamic surface expansion of Al, W, and C targets are also quantitatively characterized by time-resolved reflectance, revealing the expansion speed as well as further dielectric properties of the high-temperature-pressure phase.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.