Population lensing effect in Cr:LiSAF probed by Z-scan technique

An experiment has been performed for measuring a nonlinear refractive index that is due to the polarizability difference ΔαP between excited (4T2) and ground (4A2) states in a Cr3+:LiSAF crystal at λ = 647 nm. The latter one is responsible for a population lensing effect which has been monitored by using the eclipsing Z-scan technique. We have performed a data analysis that allows to distinguish between thermal and population contributions to the lensing effect. We have found ΔαP = 4.6 × 10−25 cm3 which is in a good agreement with our previous measurements with a different technique.