Absorption saturation analysis of Cr^2+:ZnSe and Fe^2+:ZnSe

We propose several methods for the accurate determination of the cross sections of solid-state saturable absorbers and apply them to the analysis of polycrystalline Cr2+:ZnSe and Fe2+:ZnSe. In the case of Cr2+:ZnSe, both z-scan and power-dependent transmission measurements were made by using a continuous-wave fiber laser at 1800 nm and a pulsed optical parametric oscillator at 1570 nm. The average ground-state absorption cross sections at the wavelengths of 1800 and 1570 nm were determined to be 6.17×10−19cm2 and 2.24×10−19cm2, respectively. Furthermore, the ratio of the cross sections at these wavelengths (2.75) was close to the value of 2.55 obtained from absorption spectrum measurements. Excited-state absorption was found to be negligible at both wavelengths. In the case of Fe2+:ZnSe, a tunable, pulsed Cr2+:ZnSe laser was used to obtain saturation data (z-scan and power-dependent saturation) at the wavelengths of 2645 and 2730 nm. Average ground-state absorption cross sections at 2645 and 2730 nm were determined to be 1.73×10−19cm2 and 2.47×10−19cm2, respectively, again in very good agreement with those obtained from absorption spectrum measurements.