This study investigates the temporal absorption behavior of single-layer HfO2, SiO2, and anti-reflective HfO2/SiO2 dielectric coatings under ultraviolet irradiation at 343 nm and 355 nm wavelengths, as a function of laser pulse duration ranging from 170 fs to 10 ps. Absorptance was measured using photothermal common-path interferometry and analyzed with rate equation-based numerical models. The results revealed that classical multiphoton absorption alone cannot fully account for the observed temporal absorptance dynamics. A simplified model indicated that absorption via intermediate defect states may significantly contribute to the nonlinear optical response, depending on both the pulse duration and the intrinsic material properties.
Atkočaitis et al. (Wed,) studied this question.