Plasma parameters within the cathode spot of laser-induced vacuum arcs: experimental and theoretical investigations

The cathode spot formation in laser-induced breakdown in a vacuum was investigated by laser absorption photography with high spatial (0.5 μm) and temporal (100 ps) resolution. The discharge was initiated between Cu-electrodes with cathode-anode distance of 25-250 μm. The discharge duration was 750 ns and some milliseconds, the current below 10 A. Picosecond momentary absorption photography yielded spatial-temporal density distributions in the ignition phase of the cathode spot. An absolute electron density value >5×10²⁶ m^-3 in narrow plasma fragments with diameter smaller than 5 μm was estimated. Principal new physical objects-“shooting solitons”-nonstationary plasma emissive centers, generated at the moving boundary of the expanding cathode spot plasma, obtained during the analysis of computer simulations give a satisfactory explanation of the current transfer in laser-induced breakdown