Laser-induced breakdown of gases

Abstract

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. The importance of the effects of primary spherical aberration in assessing the breakdown threshold intensity is examined, and it is shown that many apparently contradictory results can be reconciled when these effects are properly taken into account.

Laser propagation and energy absorption by an argon spark

“…Both of these phenomena are treated theoretically by different groups. 7,8 In intense light, an electron can gain sufficient energy by absorbing photons from the radiation field in collision with neutral atoms to produce ionization. The multiphoton ionization process can generate the initial electrons from which an electron cascade can develop, if the laser irradiance is high enough.…”

Electric field-free gas breakdown in explosively driven generators

“…[1][2][3][4][5] Similar gas breakdown phenomena may take place in shock wave ferromagnetic and ferroelectric generators designed with explosively accelerated metallic flyer plates. In fact, in one series of our experiments, we had difficulty obtaining signals from the first of several single-turn diagnostic coils placed along the ferromagnetic element of a FMG.…”

“…In the early 1960s, it was discovered that the laser beams can induce gas breakdown. 4,5 It was experimentally demonstrated that high-power laser beams cause plasma formation and the propagation of the plasma front in gases with no metallic electrodes in the system. The ionization of gas and the formation of plasma occur due to inelastic collisions between electrons and atoms in which the interaction energy is drawn from the electromagnetic field of the light waves.…”

“…The laser-beam-induced gas breakdown was successfully used to initiate gas discharges in ultrahigh voltage spark gap switches. 5 In this brief communication, we report on experimental results that demonstrate that gas breakdown can occur with no electric field under the unique operational conditions occurring in explosively driven generators.…”

Time-resolved optical emission spectroscopy of laser-produced air plasma

“…The formation of laser-induced breakdown ͑LIB͒ plasma in a gas has been investigated since its discovery 1 resulting in several studies that have been summarized by different authors. [2][3][4][5][6][7][8][9][10][11][12][13][14] The LIB plasma develops a shock wave into the ambient medium and the gas is heated to high temperatures ͑1-3 eV͒. 15 After breakdown, the plasma becomes very opaque and an abrupt shutoff of the laser transmitted light occurs.…”