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.
Highlights
A coherent source with broad instantaneous bandwidth and absolute frequency stability has many applications
We extend our earlier work [10,11,12] by pumping at 2-μm with a Tm-fiber laser and by employing GaAs as a nonlinear element, again achieving extremely broad bandwidth output, but spanning an octave in the spectroscopically important ‘fingerprint’ band
The oscillator was pumped by a low relative intensity noise (RIN) semiconductor laser at 1564nm, which was amplified in an Er-fiber amplifier chain to an average power of 1.3W
Summary
A coherent source with broad instantaneous bandwidth and absolute frequency stability has many applications. The advent of frequency combs and excellent mode-locked fiber lasers have revolutionized precision metrology in the visible and near-infrared. A degenerate OPO is in principle a nearly ideal frequency converter [8, 9], capable of extending the benefits of frequency combs to the mid-IR through rigorous, phase and frequency locked down conversion of established mode-locked pump lasers. We extend our earlier work [10,11,12] by pumping at 2-μm with a Tm-fiber laser and by employing GaAs as a nonlinear element, again achieving extremely broad bandwidth output, but spanning an octave in the spectroscopically important ‘fingerprint’ band
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