Electro-optic and Piezoelectric Coefficients and Refractive Index of Gallium Phosphide

Measurements of the constant-strain electro-optic coefficient of GaP between 0.56 and 3.39 μ wavelength were made using both pulsed electric field and optical heterodyne techniques. At 0.6328 μ wavelength its value is −0.97×10−12 m/V. A dispersion of only 10% is present between 0.56 and 3.39 μ. Approximate values of the piezoelectric coefficient and the constant-stress electro-optic coefficient are also obtained from the analysis of the experiments. For GaP the magnitude of the constant-stress coefficient is less than the constant-strain coefficient. The analysis also points out an often ignored effect: electro-optic measurements made with electric field frequencies in the range of resonant acoustic frequencies may not exhibit the expected symmetry of the crystal plus field but may also evidence effects from the crystal shape. Accurate refractive index measurements made on many GaP crystals between 0.545 and 0.70 μ wavelength are also reported.