Radiation-induced optical response of single-crystal and polycrystalline YAG

Exposure of optical materials to transient-ionizing-radiation fields can give rise to transient and/or permanent photodarkening effects. In laser materials, such as YAG, such induced optical loss can result in significant degradation of the lasing characteristic of the material, making its selection for optical device applications in radiation environments unfeasible. In the present study, the effects of ionizing radiation on the optical response of undoped and 1.1% Nd-doped single-crystal and polycrystalline YAG have been investigated. In the undoped materials it is seen that both laser materials exhibit significant loss at the 1.06 μm lasing wavelength following exposure to a 40 krad, 30 nsec pulse of gamma radiation. In the undoped single-crystal samples, the transmission loss is initially large but exhibits a rapid recovery. By contrast, the undoped polycrystalline YAG experiences an initial 100% loss in transmission, becoming totally opaque at 1.06 μm following the radiation pulse. This loss is slow to recover and a large residual permanent photodarkening effect is observed. Nd-doping improves the optical response of the materials in that the radiation-induced optical loss is substantially smaller in both the polycrystalline and single-crystal YAG samples. Preliminary results on the radiation response of elevated-temperature samples will also be reported.