Abstract

Modulation of a helium-neon laser beam has been observed by exciting a CdS sample with the 514.5 nm output of an argon-ion laser. The strong absorption of this latter wavelength results in a surface effect which indicates the formation of a lens due to (i) the distortion of the front face of the sample, (ii) a transverse gradient in the index of refraction. In addition to the induced positive lens, a Fabry-Perot interferometer is recognized due to thermal expansion, yielding a temporal variation in the transmittivity of the HeNe beam. The above observations are modeled using a ray matrix method and dividing the sample into two sections. The front section is the one over which complete absorption of the exciting beam (514.5 nm) occurs. This results in the creation of a thin lens and a time varying interferometer. The rest of the sample is modeled as having a uniform index of refraction and a fixed thickness. The time dependent focal length of the thin lens results from two contributions: The bulging of the front face with radius of curvature R; the radial dependence of the thermally induced change in the index of refraction dn/dT.

© 1990 Optical Society of America