Measuring weak absorptance of thin film coatings by surface thermal lensing technique

In this paper, a novel sensitive and simple scheme, referred to as the surf ace thermal lensing technique (STL), has been introduced for detecting and analyzing the thermal waves to get information about weak absorptance of op tical coatings. The STL system uses an Ar ion laser and a YAG laser to pump the components at 514.5 and 1064 nm, respectively. The absorptance induced surface deformation diffracts the He-Ne probe beam into photo-power-detect or. The signal intensity was calibrated with a sample of known absorptance. Parameter studies based on Fresnel diffraction theory have also been perfo rmed to optimize experimental condition here. Several samples for the absor ptance measurements have been tested using this method, and the measurement results have been analyzed in the end.