Picosecond resolved evolution of laser breakdown in gases

Abstract

Subpicosecond pulses from a synchronously pumped dye laser were used to collinearly probe the absorption of laser breakdown plasmas formed by focusing longer (60 ps) 532 nm pulses from a regenerative amplifier into a cell containing helium, argon or nitrogen. The absolute time delay between the 532 nm pulses and the probe pulses was varied in order to measure the initiation time and the rate of growth of the plasma for different pressures and breakdown pulse energies. In general, at the higher pressures, for which cascade ionization processes are expected to dominate, the onset of the plasma is found to be quite abrupt compared with the duration of the breakdown pulse. The initiation time is earlier and the rate of growth is faster if the breakdown pulse energy or pressure is increased. For argon and nitrogen at lower pressures, slow growth of the plasma can continue for hundreds of picoseconds after the breakdown pulse has passed, indicating that relaxation from a non-equilibrium state occurs.

History

“…The result of 60 ps Nd:YAG 532 nm pulses was reported by Davis et al (Davis et al, 1993). Kagawa et al (Kagawa et al, 1994) wrote on XeCl excimer laser-induced shock wave plasmas and applications to emission spectrochemical analysis.…”