Tunable high-average-power optical parametric oscillators near 2 μm

We report on the development of high-average-power nanosecond and picosecond laser sources tunable near 2 μm based on optical parametric oscillators (OPOs) pumped by solid-state Nd:YAG and Yb-fiber lasers at 1.064 μm. By exploiting 50-mm-long MgO-doped lithium niobate (MgO:PPLN) as the nonlinear crystal and operating the OPO in a near-degenerate doubly resonant configuration with intracavity wavelength selection elements, we have generated tunable high-average-power radiation across 1880–2451 nm in high spectral and spatial beam quality with excellent output stability. In nanosecond operation, pumping with a Q-switched Nd:YAG laser and using an intracavity prism for spectral control, we have generated more than 2 W of average power in pulses of 10 ns duration at 80 kHz repetition rate with narrow linewidth (<3  nm), with M2<2.8, and a passive power stability better than 2.2% rms over 1 h. In picosecond operation, pumping with a mode-locked Yb-fiber laser and using a diffraction grating as the wavelength selection element, we have generated more than 5 W of average power in pulses of 20 ps at 80 MHz repetition rate with narrow bandwidth (∼2.5  nm), with M2<1.8 and a passive power stability better than 1.3% rms over 2 h. The demonstrated sources represent viable alternatives to Tm3+/Ho3+-doped solid-state and fiber lasers for the generation of high-power radiation in the ∼2  μm spectral range.