The differential cross section for the electron scattering accompanied by simultaneous absorption or emisson of one Raman photon and the inverse bremsstrahlung process in an intense laser beam is calculated.

Studies of breakdown threshold intensity for air at various pressures in the range of 24–760 torr using 0.355, 0.532 and 1.06 µm radiation are reported. We observep^−0.8 scaling ofI_th at 1.06 µm and a weak scaling ofp^−0.4 at 0.532 and 0.355 µm radiation. Strong dependence of breakdown spot size on laser power but weak dependence on air pressure is observed.

Doppler-limited high resolution laser optogalvanic spectra of six transitions of rhenium lying in the range 560–620 nm have been recorded. Isotope shifts between the two natural isotopes of rhenium,¹⁸⁵Re and¹⁸⁷Re, have been calculated in all the six transitions. Hyperfine coupling constants for eight levels belonging to the configurations 5d⁵6s², 5d⁶6s, 5d⁴6s²6p and 5d⁵6s6p are reported. Wherever possible our constants are compared with those given by others.

A one dimensional numerical model to simulate the laser matter interaction in the presence of an ambient gas is presented. The model is developed by making appropriate modifications in MEDUSA, a one dimensional Lagrangian computer code, which simulates laser plasma interaction in vacuum. Various parameters of the plasma such as velocity, electron temperature, ion temperature, density, pressure, shock wave intensity of the plasma as it expands into a background gas are simulated. The results are compared with the experimental observations.