Interaction of super-intense light fields with atoms and surfaces

Using amplified 100 fs, 616 nm pulses, we employed pump-probe spectroscopy to investigate strong field interactions with gases and metal surfaces. The ionization dynamics of a gas with a pump pulse foeused to 1016 W/cm2 were deduced from spectral shifts in a probe pulse. In addition to above threshold ionization, impact ionization and a nonlinear dependence of the collision frequency on pulse intensity are proposed as mechanisms for the spectral shifts. Also, the cooling time of a high-temperature solid density plasma was measured specifically, the nonequiibrium electron energy distribution excited by a resonantly absorbed pulse focused to 5 x 1012 W/cm2 on a metal surface was measured with a photoelectron time-offlight detector.