Measurements of Dynamic Optical Distortion in Nd-Doped Glass Laser Rods

Abstract

This paper quantitatively describes the optical distortion in neodymium-doped glass which is induced by pump radiation. We have found the optical path length at 6328 Å dependent on four primary effects: (1) change in physical length; (2) change in refractive index due to temperature rise; (3) change in index resulting from stress; (4) change in index associated with an excited-state population of neodymium ions. Section I presents the experimental techniques used and the results obtained. Included in this section are measurements of optical-path-length variations, pump-induced birefringence, change in physical length, change in refractive index, bulk temperature rise, and the deflection of a pencil of rays. Section II compares the results of Section I with the theory set forth in the previous paper. Good agreement between theory and experiment is achieved provided a term which takes account of the index change associated with an excited-state population of neodymium ions is included. This term arises from the fact that the polarizability of the neodymium ion in its excited 4F3/2 level is different from its value in the 4I9/2 ground level. The inclusion of this new term in the expression for the change in refractive index implies that large optical distortions can exist in ``athermalized'' glass.