Octave-spanning ultrafast OPO with 26-61µm instantaneous bandwidth pumped by femtosecond Tm-fiber laser

TLDR

Resonator group dispersion and intracavity absorption/dispersion critically determine the instantaneously broad bandwidth and spectral stability of degenerate OPOs. The study extends broadband degenerate OPO operation further into the mid‑infrared. A 2050‑nm femtosecond Tm‑fiber laser synchronously pumps a 500‑µm‑long orientation‑patterned GaAs crystal to generate broadband gain centered at 4.1 µm. The OPO achieves a 17‑mW pump threshold, delivers 37 mW average output, and spans 2.6–6.1 µm at the –30 dB level.

Abstract

We report the extension of broadband degenerate OPO operation further into mid-infrared. A femtosecond thulium fiber laser with output centered at 2050 nm synchronously pumps a 500-μm-long crystal of orientation patterned GaAs providing broadband gain centered at 4.1 µm. We observe a pump threshold of 17 mW and output bandwidth extending from 2.6 to 6.1 µm at the -30 dB level. Average output power was 37 mW. Appropriate resonator group dispersion is a key factor for achieving degenerate operation with instantaneously broad bandwidth. The output spectrum is very sensitive to absorption and dispersion introduced by molecular species inside the OPO cavity.