Time-Resolved Study of Nonlocal Electron Heat Transport in High Temperature Plasmas

Exploiting the high absorption efficiency of intense, ultrashort laser pulses in gases of atomic clusters we have created plasma filaments with temperatures of >1keV and electron densities in excess of 10²⁰cm^-3. Using picosecond laser pulses, we have interferometrically measured the temporal and spatial evolution of the electron density in these plasmas on a fast (<50ps) time scale. Our measurements indicate that nonlocal heat transport by hot electrons drives a fast ionization wave, and the data agree well with a nonlocal heat transport model.