Yb-fiber laser pumped high-power, broadly tunable, single-frequency red source based on a singly resonant optical...

We present an efficient and tunable source generating multi-watt single-frequency red radiation by intra-cavity frequency doubling of the signal in a MgO-doped periodically poled LiNbO₃ (MgO:PPLN)-based singly resonant optical parametric oscillator (SRO). By optimally designing the SRO cavity in a six-mirror configuration, we generate ≈276  nm tunable idler radiation in mid-infrared with a maximum power of P_i=2.05  W at a pump power of P_p=14.0  W. The resonant signal is frequency doubled using a 10 mm-long BiB₃O₆ (BiBO) crystal which resulted in tunability of a red beam from ≈753 to 780 nm band with maximum power P_r≈4.0  W recorded at λ_r≈756  nm. The deployment of a six-mirror SRO ensures single-frequency generation of red across the entire tuning range by inducing additional losses to Raman modes of LiNbO₃ and, thus, inhibiting their oscillation. Using a scanning Fabry-Perot interferometer (FPI), nominal linewidth of the red beam is measured to ≈3  MHz which changes marginally over the entire tuning range. Long-term (over 1 h) peak-to-peak frequency fluctuation of the generated red beam is estimated to be about 3.3 GHz under free-running conditions at P_p=14.0  W. The generated red beam is delivered in a TEM₀₀ mode profile with M²≤1.32 at maximum power in a red beam.