Laser-induced discharges in vacuum and air: diagnostics of an extreme states of matter

Picosecond laser pulses at a wavelength of 1064 nm have been focused onto a copper cathode in coincidence with an electric field to produce a laser induced breakdown in vacuum and onto anode surface (Ag, Pd, W, AuNi electrodes) for laser-induced discharge in air. At a power density of about 3/spl times/10/sup -13/ W/cm/sup 2/, the formation of local regions with high pressures and temperatures in an electrode gap was investigated. As a result of an intensive energy deposition in a small volume, a strongly coupled microplasma was formed: properties varied during nonstationary processes of heating and hydrodynamic motion over a wide range of the phase diagram, from a Fermi-like to an ideal plasma. As an experimental diagnostic, the authors used laser absorption photography with high temporal (100 ps) and spatial (<1 /spl mu/m) resolution, which allowed us to determinate the spatial-temporal density distribution in the ignition phase of laser-induced discharges, as well as a registration of X-ray radiation by means of picosecond X-ray streak camera. The pulsed bursts of a strongly directed X-ray radiation reveal a nonstationary appearance of extreme states of matter in small localized plasma volume.