Piezooptic coefficients of four neodymium-doped laser glasses Roy M. Waxier and Albert Feldman

U.S. National Bureau of Standards, Ceramics, Glass, and Solid State Science Division, Center for Materials Science, Washington, D.C. 20234. Received 22 April 1980. In this Letter we present the results of our measurements

of the piezooptic coefficients of four new Nd-doped laser glasses: phosphate glass Q-88 made by Kigre, Incorporated, and three fluorophosphate glasses: LG-812 produced by Schott Optical Glass, Incorporated; E-181 manufactured by Owens-Illinois, Incorporated, and LHG-10 made by Hoya Optics Corporation.1 The coefficients were measured at 0.6328- and 1.15-μm wavelengths. The photoelastic constants of several other laser glasses have been reported earlier2, and part of the data given here on these newest laser glasses have appeared in an earlier publication.3

Glasses that are isotropic possess two independent absolute piezooptic constants, q11 and q12,4,5 and these can be deter­mined by the use of interferometric techniques that measure the stress-induced change of refractive index. We can also independently determine the difference (q11 — q12) from measurements of stress-induced birefringence.

Measurements were made on rectangular glass blocks with dimensions approximately 13 X 13 X 37 mm. Two opposite long faces of each prism were polished flat and nearly parallel so that about six Fizeau-type fringes could be observed be­tween the faces when illuminated by laser light at 0.6328 μm. The specimens were then mounted in a stressing apparatus specially constructed for piezooptic measurements.6

The specimens were loaded in compression, and the optic path change of the radiation propagating through the speci­men was measured by means of two types of interferometers, a Fizeau and a Twyman-Green. The combined use of Fizeau and Twyman-Green interferometry to determine q11, q12, and the elastic compliance coefficient S12 has been described previously.7_10 The coefficient for stress-induced birefrin­gence, q11 — q12, was determined by a polarimetric tech­nique.10

In all the experiments, each measurement was repeated forty times, and from these data a mean value and standard deviation were calculated. An error analysis was used in subsequent calculations to find the standard deviation of each coefficient. The resulting Values for q11, q12, (q11 — q12), and S12 are shown in Table I, which also gives the zero-stress linear

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Table I. Piezooptic Coefficients and Elastic Compliance Coefficient, s12 ,

of Neodymlum-Doped Laser Glasses (10_12Pa−1)

index n0 and the relative stress-optic coefficient C defined by C = n3/2(q12 − q11). Values of n0 were obtained from the Lawrence Livermore Laboratory.11

The table shows LHG-10 to have the smallest stress bire­fringence coefficient and LG-812 and E-181 to have the smallest absolute coefficients. Phosphate glass Q-88 has the largest piezooptic coefficients. The values of s 12 are close for the four glasses. The coefficients appear to be only slightly smaller at 1.15 μm than at 0.6328 μm.

This work was supported in part by the Lawrence Liver-more Laboratory of the Department of Energy.

References 1. Commercial materials are identified in this paper to specify the

particular substance on which the data were obtained. In no instance does such identification imply recommendation or en­dorsement by the National Bureau of Standards or that the ma­terial identified is necessarily the best for the purpose.

2. R. M. Waxier, G. W. Cleek, J. H. Malitson, M. J. Dodge, and T. A. Hahn, J. Res. Natl. Bur. Stand. Sect. A: 75, 103 (1971).

3. R. M. Waxier, A. Feldman and D. Horowitz, in Laser Induced Damage in Optical Materials: 1978, NBS Special Publication 541, A. J. Glass and A. H. Guenther, Eds. (U.S. GPO, Wash. D.C., 1978), pp. 50-54.

4. K. Vedam, Proc. Indian Acad. Sci. Sect. A 31, 450 (1950). 5. J. F. Nye, Physical Properties of Crystals (Oxford U.P., London,

1951), pp. 243-254. 6. A. Feldman and W. J. McKean, Rev. Sci. Instrum. 46, 1588

(1975). 7. F. Twyman and J. N. Perry, Proc. Phys. Soc. London 34, 151

(1922).

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8. A. Feldman, R. M. Waxier, and D. Horowitz, Optical Properties of Highly Transparent Solids, S. S. Mitra and B. Bendow, Eds. (Plenum, New York, 1975), pp. 517-525.

9. A. Feldman, Electro Opt. Syst. Des. 8, 36 (1976). 10. A. Feldman, Opt. Eng. 17, 453 (1978). 11. S. Stokowski, Lawrence Livermore Laboratory; personal com­

munication.