This work represents the first stress-optical study of strontium titanate (SrTiO3). The report includes a brief review of previous stress-optical work on crystals, a brief review of synthetic SrTiO3, and a brief review of stress-optical theory. The remainder of the paper is divided into two parts: Part I describes the piezobirefringence experimental apparatus and experimental procedure, sources of error and corrections, the measured values of the piezobirefringence constants (q2211-q1111) and 2q1212 for the spectral range 4200–7700 A in steps of 100 A, an investigation of the linearity of the stress-optical relationship up to "moderate" pressures, and an investigation of stress-optical hysteresis up to "moderate" pressures. Part II covers the following: the problem of measuring the absolute values of stress-optical constants q1111 and q2211, apparatus and procedure, sources of error, the measured values of the stress-optical constants at 5400 A, the theoretical change in index of refraction under an hydrostatic stress, and confirmation of the linearity of the stressoptical relationship up to "moderate" pressures.
Strontium titanate has been found to become an optically negative uniaxial crystal when stressed along a crystallographic axis and an optically negative biaxial crystal when under a crystallographic diagonal stress.
A. A. GIARDINI, "Stress-Optical Study of Strontium Titanate," J. Opt. Soc. Am. 47, 726-729 (1957)