Measurement of saturation intensities in ion doped solids by transient nonlinear refraction

The transient response of the Z-scan signal ΔT(t) was used to investigate the nonlinearity of ion doped solids. n2 measurements in ruby and alexandrite were performed using an Ar+ laser. We observed that the nonlinearity response time τ decreases with the laser intensity as τ−1=τ0−1(1+I/Is), where τ0 is the excited state lifetime and Is the transition saturation intensity. So, by measuring the transient response at different laser intensities, we were able to determine not only the nonlinear complex refractive index n2 but also τ0 and Is for Cr+3 in ruby and in the two alexandrite sites.