The transient response of theZ-scan signal&Dgr;T(t)was used to investigate the nonlinearity of ion doped solids.n2measurements in ruby and alexandrite were performed using anAr+laser. We observed that the nonlinearity response time &tgr; decreases with the laser intensity as&tgr;−1=&tgr;0−1(1+I/Is), where&tgr;0is the excited state lifetime andIsthe transition saturation intensity. So, by measuring the transient response at different laser intensities, we were able to determine not only the nonlinear complex refractive indexn2but also&tgr;0andIsforCr+3in ruby and in the two alexandrite sites. ©1997 American Institute of Physics.