THE INFLUENCE OF THERMAL-EXPANSION OF SOLIDS ON THE MIRAGE-EFFECT SIGNAL

The bouncing configuration of the mirage method has several advantages over the skimming one. Although the signal in this configuration is t hought to be due to the variation in refractive index of the surroundi ng gas alone, it may also be influenced by the thermal expansion of th e investigated sample. In this paper, three-dimensional calculations o f the deflection of the probe beam from the surface vibrations are pre sented and the effect of the probe beam's finite size is calculated. B oth the transverse and the normal components of the signal are conside red. The photodeflection signal obtained is compared with the mirage s ignal and the effects of various experimental conditions are discussed . The theoretical predictions are compared with experimental data from materials of various thermal diffusivities and thermal expansion coef ficients.