Picosecond pulse formation in the presence of atmospheric absorption

Mode-locked mid-infrared (MIR) fiber laser research has been dominated by the generation of pulses in the picosecond regime using saturable absorbers (SAs) and more recently frequency shifted feedback (FSF). Despite the significant emphasis placed on the development of materials to serve as the SAs for the MIR, published pulse durations have been substantially longer than what has been reported in the near-infrared (NIR). In this report we present experimental data supporting the view that the majority of demonstrations involving SAs and FSF have been limited by the presence of molecular gas absorption in the free-space sections of their cavities. We show that the pulse duration is directly linked to the width of an absorption-free region of the gaseous absorption profile and that the resulting optical spectrum is nearly always bounded by strong absorption features. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

Research on mode-locked mid-infrared fiber lasers has mainly focused on generating picosecond pulses using saturable absorbers and frequency shifted feedback. However, the pulse durations reported in this field have been longer than those in the near-infrared region, largely due to limitations caused by molecular gas absorption in the free-space sections of the laser cavities. This study indicates that the pulse duration is directly related to the width of an absorption-free region in the gas absorption profile, with the resulting optical spectrum typically bounded by strong absorption features.