## Abstract

To assess the suitability of bismuth germanate as an electro-optic material for high precision applications, we have confirmed and extended previous data on its refractive index, electro-optic tensor element *r*
_{41}, and thermal expansion coefficient. In addition, we have measured the thermo-optic coefficient d*n*/d*T*, the temperature dependence of the electro-optic coefficient, and the stress-optic tensor elements. From the stress-optic tensor elements and previously published data, we have computed the strain-optic tensor elements. The index of refraction is given, to a good approximation, by the single-term Sellmeier equation, *n*
^{2} − 1 = *s*
_{0}λ_{0}
^{2}/[1 − (λ_{0}/λ)^{2}], with *s*
_{0} = 95.608 μm^{−2} and λ_{0} = 0.1807 μm. The thermo-optic coefficient is 3.9 × 10^{−5}/°C at 632.8 nm and 3.5 × 10^{−5}/°C at 1152.3 nm. The electro-optic tensor element varies between approximately 1.05 and 1.11 pm/V over the spectral range of 550–1000 nm; its normalized effective change with temperature is approximately 1.54 × 10^{−4}/°C. The thermal expansion coefficient is 6.3 × 10^{−6}/°C over the range 15–125 °C. Values of the stress-optic tensor elements are *q*
_{11} − *q*
_{12} = −2.995 × 10^{−13} m^{2}/N and *q*
_{44} = −0.1365 3 10^{−12} m^{2}/N. The strain-optic tensor elements are *p*
_{11} − *p*
_{12} = −0.0266 and *p*
_{44} = −0.0595.

© 1996 Optical Society of America

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