Piezo-optic coefficient of gallium nitride

Gallium nitride is a material of interest for a range of optical and optoelectronic applications, including its use in blue light LEDs, efficient solar cells, and high power optoelectronic devices for communications, radar, and power amplifiers. During high power operation, these devices develop temperature gradients which cause changes in the local refractive index due in part to the piezo optic effect, resulting in distortion of the output beam. Therefore, measurement of the piezo-optic coefficients is required to predict the performance of high power optoelectronic devices.
Uniaxial mechanical stress was applied to a sample of gallium nitride, which induced a birefringence in the sample. The magnitude of the induced birefringence was determined by shining polarized light from a HeNe laser through the sample at pressures between .5 and 10 MPa, passing the output beam through a rotating polarizer and measuring the intensity as a function of relative polarizer position. From the induced birefringence, the piezo-optic coefficient of gallium nitride was determined.