Development of a thermographic laser calorimeter.

A thermographic laser calorimeter for the measurement of absorptance in optical coatings is described. The heat transport equation is solved for a laser-heated disk with a thin-film coating. The solutions are used to calculate the output characteristics of the thermographic scanning system. The absorption and the thermal conductivity of oxide coatings (SiO2, TiO2, HfO2, Al2O3, and Ta2O5) were measured. Results lead to the conclusion that there is a considerable difference between the thermal properties of the coating and the corresponding bulk material.