1-Watt SESAM-Modelocked fs-Cr:ZnS Oscillator at 2.4 µm

Abstract

Cr:ZnS lasers delivering mid-infrared (mid-IR) femtosecond (fs) pulses directly from an oscillator have seen a substantial progress in research over the last decade [1] , [2] . Both power and pulse width scaling have been the main focus of the research. Such lasers are especially useful to drive efficient nonlinear processes to generate broadband long-wave infrared sources for high-sensitivity spectroscopy in the molecular fingerprint region [3] . Current state-of-the-art fs-Cr:ZnS lasers are based on Kerr-lens modelocking (KLM), where few-cycle pulses and watt-level average power have been achieved [2] , [4] . While KLM is suitable for few-cycle pulses, SESAM modelocking offers several other advantages including self-starting low-noise modelocking, robust laser cavities, and potential for a wide range of repetition rates ( f rep ). However, the lack of suitable mid-IR SESAMs has limited the average power to below 200 mW for femtosecond SESAM-modelocked Cr:ZnS lasers. In this work, we have developed a novel high-performance type-I InGaSb/GaSb quantum well (QW) SESAM, and demonstrate Cr:ZnS laser at 2.37 µm delivering 120 fs pulses at 1 watt average output power with f rep of 250 MHz. Similar laser performance is achieved even when the laser cavity is shortened to deliver fundamental modelocking pulses at f rep of 500 MHz.