High-Power Single-Frequency Source in the Mid-Infrared Using a Singly Resonant Optical Parametric Oscillator Pumped by Yb-Fiber Laser

We present a high-power single-frequency continuously tunable mid-infrared (MIR) singly resonant optical parametric oscillator (SRO) using 80-mm-long MgO-doped PPLN (MgO:PPLN) crystal pumped by a continuous-wave Yb-fiber laser. The SRO having four-mirror ring-cavity configuration is tunable in the MIR band of 3761-3970 nm yielding a maximum power of 2W at 3895 nm when incident pump power is ≈16W. Due to strong phonon-polariton coupling in MgO:PPLN crystal, the intracavity signal-beam spectrum exhibits multiple peaks depicting stimulated polariton scattering. By replacing one of the cavity mirrors with a 5% outcoupler, the stimulated polariton modes are suppressed as a consequence of additional cavity losses. Along with a tunable signal extending from 1453 to 1484 nm, we obtained the maximum signal power of ≈4W at 1464 nm at the maximum pump power of ≈16W. In addition, we have measured the frequency and power stability of the outcoupled signal and idler beams over long as well as short durations. The improvement in beam quality of idler was discernible when the intracavity signal was outcoupled, which is essentially a consequence of reduced thermal load on MgO:PPLN crystal.