Transverse photothermal beam deflection within a solid

The mirage effect within a transparent solid substrate was used for monitoring optical absorption of a thin film. Refractive index gradients, which accompany thermal gradients below the film‐coated surface, cause a probe laser beam to be deflected. The spectrum of copper, deposited onto a piece of clear acrylic, was recorded by this method of photothermal deflection. The influence of thermally induced mechanical stresses can alter the effective value of the thermo‐optic coefficient of the solid, dn/dT.