High-sensitive absorption measurement in transparent isotropic dielectrics with time-resolved photothermal common-path interferometry

We propose a time-resolved photothermal common-path interferometry scheme at fast heating in the absence of heat diffusion and employ it to measure absorption in Suprasil 311 silica glass (2.8·10-6 cm-1) at a wavelength of 1071 nm and continual absorption in laboratory air (2.9·10-8 cm-1) for a signal-to-noise ratio of 100/1. The absorption was measured at a thermally induced phase incursion of less than 0.1 rad in a heating beam, which guaranteed correct calibration. To calibrate this scheme, we developed a theory of diffraction on deformations taking into account the stresses arising in an inhomogeneous temperature field. This allowed us to use a standard glass K8 for calibration. The low level of noise and time resolution of pulsed signals allowed the distinguishing of the contributions of Kerr and striction nonlinearities to absorption measurements in Suprasil 311 silica glass and enabled the observance of the time evolution of strictional deformations. Additionally, an anomalous temporal development of the absorption of broadband laser radiation in atmospheric air at 2.9·10-8 cm-1 has been revealed.