Simulation of nonlinear optical absorption in ZnSe:Co 2+ crystals

The paper presents theoretical approach to simulation of nonlinear optical absorption in zinc selenide crystals doped with cobalt (II) ions (ZnSe:Co ²⁺), which was reported by us earlier (Opt. Laser Technology, V. 35, (2003), 169). We used ZnSe:Co ²⁺ crystals as saturable absorbers for generation of giant-pulse eye-safe laser radiation. It was found that minimal optical losses (maximal final transmission) occurred for ZnSe samples containing 1.6×10 ¹⁹ cm ^-3 of Co ²⁺ ions. Band structure and photoinduced molecular dynamics simulations were performed to explain the parabolic dependence of optical losses versus Co ²⁺ concentration. The minimum was shown to be the result of photoinduced anharmonic electron-phonon interaction.