Measurements of the anisotropic nonlinear refractive-index coefficients of ruby

The real part n(2)' of the complex nonlinear refractive-index coefficients of ruby crystal (Cr(3+):Al(2)O(3)) are measured by the Mach-Zehnder interferometric method. The n(2)' values measured at 514.5 nm for the light polarization perpendicular (sigma) and parallel (pi) to the crystal c axis are (2.81 +/- 0.36) 10(-8) and (1.33 +/- 0.17) x 10(-8) cm(2)/W, respectively. From the results obtained the ratio of the polarizability difference between the excited and ground states of Cr(3+) in ruby for sigma polarization to that for pi polarization is found to be 1.05 +/- 0.30.