Nonlinear absorption phenomena in optical materials for the UV-spectral range

A laser calorimetric technique is employed to measure absorptance and laser-induced changes therein on optical components at 248 nm. In BaF2, a linear increase of absorptance with intensity is observed, but a pure two-photon absorption mechanism can be ruled out because the slope lessens towards shorter pulse lengths. Fused silica, at moderate energy densities, exhibits a reversible, linear absorption increase with energy density; an AR-coated sample mirrors the behavior of the uncoated substrate but discloses an added offset due to coating imperfections. In a series of measurements at constant irradiation parameters, uncoated substrates of Suprasil and CaF2 reveal a slight exponential decrease in absorptance which might be attributed to surface cleaning or conditioning effects, and absolute absorptance is virtually independent of the sample thickness.