Power and noise dynamics in SESAM modelocked GHz-class SWIR solid-state lasers

Gigahertz-class femtosecond lasers in the short-wave infrared (SWIR) are increasingly important for high-precision spectroscopy and efficient nonlinear conversion but require stringent power and noise performance. Semiconductor saturable absorber mirror (SESAM) modelocking is a robust approach for generating stable GHz-class lasers, yet the impact of SESAM and cavity parameters in the SWIR remains insufficiently understood. Here, we investigate the power and noise dynamics of a 1-GHz SESAM modelocked Cr:ZnS laser, revealing a direct link between SESAM and cavity parameters and the resulting relaxation oscillations. By engineering the SESAM modulation depth, we uncover a fundamental power-noise trade-off: higher modulation depth suppresses relative intensity noise (0.05% integrated over [10 Hz, 10 MHz]) and timing jitter (62 fs over [2 kHz, 10 MHz]) while operating at an average output power of 93 mW, whereas low modulation depth enables power scaling up to 0.8 W at the expense of increased noise (0.94% integrated RIN [10 Hz, 10 MHz] and 187 fs integrated timing jitter [2 kHz, 10 MHz]). Supported by numerical simulations, these results provide a practical framework for optimizing GHz SWIR lasers for application-specific performance.