SESAMs for High-Power Oscillators: Design Guidelines and Damage Thresholds

We present for the first time to the best of our knowledge a systematic study of lifetime and damage of semiconductor saturable absorber mirrors (SESAMs) designed for operation in high-power oscillators. We characterize and compare nonlinear reflectivity and inverse saturable absorption (ISA) parameters as well as damage threshold and lifetime of different representative SESAMs under test using a nonlinear reflectivity measurement setup at unprecedented high fluence levels. We investigate the catastrophic damage that occurs at very high fluences by demonstrating a dependence of the damage threshold on the ISA parameter F₂ and the maximum reflectivity fluence F₀. We can clearly demonstrate that the damage fluence F_d scales proportionally to √F₂ for all SESAMs. In the case of SESAMs with the same absorber where the product F_sat .ΔR is constant, the damage fluence F_d scales proportionally to F₀. Therefore, damage occurs due to heating of the lattice by the energy absorbed due to the ISA process and is not related to the quantum well (QW) absorbers. Furthermore, we present guidelines on how to design samples with high saturation fluences, reduced induced absorption, and high damage thresholds. Using multiple QWs and a suitable di-electric topsection, we achieved SESAMs with saturation fluences >;200 μj/cm², nonsaturable losses <;0.1%, and reduced ISA. Our best sample could not be damaged at a maximum available fluence of 0.21 J/cm² and a peak intensity of 370 GW/cm². These SESAMs will be suitable for future high-power femtosecond oscillators in the kilowatt average output power regime, which is very interesting for attosecond science and industrial material processing applications.