TWO-PHOTON ABSORPTION IN ALKALI HALIDES WITH A PULSED N2 LASER

Abstract

Two-photon absorption has been observed in alkali halide crystals with a 1 MW superradiant pulse at 3371 Å from a nitrogen gas laser. This multiple quantum process is equivalent to a single-photon absorption in the fundamental absorption edge of the alkali halide with the formation of an exciton and its subsequent trapping at an imperfection to form an F center. The crystals were visibly colored in the regions of high laser flux density. These colored regions, similar to color centers produced by ultraviolet radiation in the exciton region, were bleached by radiation in the F center absorption band.