Laser-induced breakdown of gases

Powerful flashes of ultraviolet, visible and near-infrared laser light can cause breakdown and plasma formation in gases which are normally transparent at these wavelengths. The ionization processes involved are multiphoton absorption and inverse bremsstrahlung or cascade collisional ionization, in competition with deionization by diffusion, recombination and radiative energy losses. The relative importance of these mechanisms and their roles in leading to the initiation of breakdown and the earliest stages of plasma formation is examined. Theoretical treatments are summarized, and experimental results obtained with a variety of gases and metal vapours at pressures from millitorrs to hundreds of atmospheres and with flashes from picosecond duration to quasi-continuous illumination are reviewed.