Laser modulation photothermal radiometer—a new method for measuring weak absorption in bulk materials and coatings

A new method was developed for measuring weak absorption in bulk materials and coatings. It is based on recording a change in the integrated thermal radiation flux from the surfaces of samples heated by periodic laser radiation pulses. The possibility is discussed of making absolute measurements by simulation of surface heat sources in the materials investigated, and also by comparing them with standard samples. The sensitivity of the method is estimated and the results of absorption measurements on a number of materials are presented. Consideration is given to limitations imposed on the operating range of laser pulse repetition frequencies by the thickness of the layer of the substance emitting the thermal flux and by the increase in the transverse dimensions of the illuminated area arising on account of thermal diffusion.