Evolution of active-medium perturbations and the focusing of radiation from photodissociation lasers utilizing "slow" pumping

A theoretical investigation was made of the evolution of the radial gradient of the refractive index of the active medium in a photodissociation iodine laser amplifier of nanosecond pulses utilizing slow pumping. Two mechanisms were taken into account in discussing the appearance of an optical inhomogeneity in the medium: the excitation of acoustic waves in the laser cell during pumping in the interior and near the walls. It became clear that the amplitudes of both waves could be made to pass through a minimum simultaneously by choosing the composition of the active gaseous medium. It was concluded, on the basis of the results obtained, that if the pulse being amplified is applied at this moment of time there will be a negligible deterioration in the focusing of the beam.