Temperature and pressure variation of the refractive index of diamond.

The temperature and pressure variations of the refractive index for a Type IIa diamond have been measured at audio frequencies using capacitance techniques. Measurements have been made at zero pressure over the 5.5-340-K temperature range and at pressures up to 1.4 x 10(8) Pa (1.4 kbar) at room temperature. At room temperature, (1/n)(dn/dT)(p) = +4.04 x 10(-6)/K and (1/n)(dn/dp)(T) = -0.36 x 10(-12)/Pa. In addition, the curvature in the refractive index with temperature has been determined. The first-order derivatives are compared with previous experimental data and the recent theoretical calculations of Van Vechten and Yu and Cardona.