PLASMA PARAMETERS WITHIN THE CATHODE SPOT OF LASER-INDUCED VACUUM ARCS - EXPERIMENTAL AND THEORETICAL INVESTIGATIONS

Cathode spot formation in laser-induced breakdown in vacuum was invest igated by laser absorption photography with high spatial (0.5 mu m) an d temporal (100 ps) resolution, The discharge was initiated between Cu electrodes with a cathode-anode distance of 15-250 mu m, The duration of pulsed discharges was 750 ns and dc discharges some milliseconds; the current was below 10 A, Picosecond momentary absorption photograph y yielded spatial-temporal density distributions in the ignition phase of the cathode spot, An absolute electron density >5 x 10(26) m(-3) i n narrow plasma fragments with a diameter smaller than 5 mu m was esti mated, Mathematical modeling has satisfactorily explained the formatio n of the narrow plasma channel due to the bulk current self-focusing, as well as due to the generation of nonstationary emissive centers at the moving boundary of the expanding cathode spot plasma.