Breakdown in the rare gases using single picosecond ruby laser pulses

Abstract

An experimental investigation has been made of laser-induced breakdown thresholds in the rare gases, using single picosecond pulses from a ruby laser with time durations of 18+or-4 ps. Breakdown threshold intensity measurements, carried out at pressures below approximately 7000 Torr, were always pressure-dependent. The results show important differences from those already obtained on picosecond timescales at the same wavelength of 0.694 mu m, but are in general agreement with similar measurements made at laser wavelengths of 1.064 and 0.53 mu m. They support the view that present multiphoton ionization theory is inadequate for describing ionization in high ( gamma approximately=1) radiation fields.

Limitations on Conversion Efficiency Due to Competing Effects

“…(23b) as β 1ί -> 0: A 3 = i 1 l A l l ( l _ (26) An example of such a situation is if multiphoton ionization involving one p u m p and one harmonic photon can occur but there no resonances that can contribute to multiphoton absorption at the fundamental.…”

Laser-generated localized freestream perturbations in supersonic and hypersonic flows

“…8 , 9 Implicit in this relation is the assumption that the gas remains at a xed temperature. Typically, this has been a valid assumption because the majority of the experimental investigations of laserinduced breakdown seem to have been made in xed-volume, uninsulated test cells where the gas is at ambient temperature (see, for example, Armstrong et al 8 or Dewhurst 10 ). That the threshold intensity is actually a function of the gas density may be seen in the report by Grey Morgan, 5 where the threshold intensity is expressed in terms of the neutral molecule concentration for both ionization mechanisms.…”

Influence of secondary ionization processes on the breakdown of nitrogen by a wide range of laser wavelengths

“…Studies of laser-induced ionization and breakdown in gases have shown that multi-photon absorption and inverse Bremsstrahlung are the two main electron generation mechanisms controlling this phenomenon (see, for example, Grey Morgan 1975, Dewhurst 1977, Mainfray and Manus 1991, Corkum 1993, Fittinghoff et al 1994. The relative importance of these two processes is expected to change dramatically with both gas pressure and laser photon energy.…”