2-PHOTON ABSORPTION IN SEMICONDUCTOR-DOPED GLASSES

We report the intensity-dependent transmission of a 1054-nm laser in four Schott color glass filters: OG550, OG590, RG665, and RG850. The linear absorption is negligible, and the main mechanism of energy loss is by two-photon absorption. At higher input intensities, additional absorption due to laser-generated carriers was observed. This was confirmed by measuring the absorption of a probe beam delayed by 250 ps relative to a strong pump beam. The electron-hole pair absorption cross sections thus obtained were found to explain quite well the overall intensity-dependent transmission data. The density of laser-generated carriers is much larger in our experiments than in most of the earlier reported one-photon resonant measurements. Even at 1054 nm these glasses suffer accumulative photodarkening at higher fluences. In the photodarkened sample, the value of the two-photon absorption coefficient is approximately half that of the fresh sample.