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

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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.

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