GaSb-based SESAM technology for mid-IR ultrafast lasers

Throughout more than two decades of developments, semiconductor saturable absorber mirrors (SESAMs) [1] have become instrumental for the development of a large variety of solid-state ultrafast lasers. To a large extent, the emergence of SESAM technology is tightly linked to the penetration of ultrafast lasers to a wide range of industrial, medical, and scientific applications. Compared to other types of passive mode-locking mechanism, their key advantage is the ability to precisely tailor the nonlinear properties, and hence the mode-locking driving force. Thus, SESAM offer customized absorption recovery time from nanosecond down to sub-picosecond level and nonlinear reflectivity ranging from as low as 0.1% to tens of percent. These features are essential to ensure a robust mode locking mechanism and a practical approach to build reliable ultrashort pulse lasers with simple architecture, self-strating and environmentally stable operation, and moderate cost. At the same time, their spectral response can be tailored to cover wavelengths ranging from visible region [2] to beyond 2 µm [3] ; this is done by employing band-gap engineering of different compound semiconductor material systems, i.e. GaAs, InP, or GaSb.