Full optical SESAM characterization methods in the 1.9 to 3-μm wavelength regime

Semiconductor saturable absorber mirrors (SESAMs) are widely used for mode-locking of various ultrafast lasers. The growing interest for SESAM-modelocked lasers in the short-wave infrared and mid-infrared regime requires precise characterization of SESAM parameters. Here, we present two SESAM characterization setups for a wavelength range of 1.9 to 3 mu m to precisely measure both nonlinear reflectivity and time-resolved recovery dynamics. For the nonlinear reflectivity measurement, a high accuracy (<0.04%) over a wide fluence range (0.1-1500 mu J/cm(2)) is achieved. Time-resolved pump-probe measurements have a resolution of about 100 fs and a scan range of up to 680 ps. Using the two setups, we have fully characterized three different GaSb-SESAMs at an operation wavelength of 2.05 mu m fabricated in the FIRST lab at ETH Zurich. The results show excellent performance suitable for modelocking diode-pumped solid-state and semiconductor disk lasers. We have measured saturation fluences of around 4 mu J/cm(2), modulation depths varying from 1% to 2.4 %, low non-saturable losses (similar to 0.2%) and sufficiently fast recovery times (< 32 ps). The predicted influence of Auger recombination in the GaSh material system is also investigated. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

Two SESAM characterization setups are presented for precise measurement of SESAM parameters, allowing for nonlinear reflectivity and time-resolved recovery dynamics measurements.