TRANSVERSE SELF-PHASE MODULATION IN RUBY AND GDALO3-CR-+3 CRYSTALS

We measured the intensity pattern of an Ar-laser beam after its passage through GdAlO3: Cr+3 and Al2O: Cr+3 (ruby) crystals. We observed distortions and the formation of spatial rings; we interpret the results as evidence of transverse self-phase modulation, as previously observed in a thermal nonlinear medium [Appl. Phys. Lett. 6, 362 (1970)] and in nonlinear thin films [Opt. Lett. 9s 411 (1984)]. We measured the transient behavior of the pattern in order to investigate the temporal response of the nonlinearity. Theoretical calculations were made by using the Kirchhoff diffraction integral, where we considered the following parameters: the nonlinear index of refraction n2 (which was previously measured by Catunda et al. [Appl. Opt. 25, 2391 (1986)], the saturation intensity Is, and the response time τ. We show that the dispersive character of the nonlinearity and its saturation behavior [n2 ∝ (1 + I/Is)-1] are important in determining the intensity pattern. Good agreement between the experimental and calculated results was verified. © 1990 Optical Society of America.