Fig. 1. Layout of the 2 µm optical parametric oscillator system. HWP, half-wave plate; FR, Faraday rotator; TFP, thin-film polarizer; L, lens; M, 45° high reflector for 1064 nm; M₁, input mirror; M₂, output coupling mirror; DM, dichroic mirror.

Fig. 2. The total 2 µm output pulse energy and efficiency of KTP-OPO with and without walk-off compensation. Inset: the spatial separation signal and idler observed without compensation.

Fig. 3. The total 2 µm pulse energy curves with OCs of T = 10%, 20%, and 30% at KTP crystal lengths and pump trips of (a) 20 mm, double-pass pump, (b) 20 mm, single-pass pump, (c) 25 mm, double-pass pump, and (d) 25 mm, single-pass pump.

Fig. 4. The effects of pump trips, OC transmittances, and cavity lengths on the total 2 µm energy output performance. Energy curves for the (a) double-pass pumped and (b) single-pass pumped 15 mm KTP-OPO. (c) Total 2 µm pulse output performance at different cavity lengths.

Fig. 5. (a) The pulse energy of the signal and idler. (b) The spectra of the signal and the idler, with central wavelengths of 2109 and 2149 nm, and spectral FWHMs of 10.6 and 10.8 nm, respectively.

Fig. 6. Waveforms of 2 µm pulse. (a) Signal pulse width and (b) idler pulse width.

Fig. 7. RMS energy stabilities of the KTP-OPO over 30 min measurement with the (a) pump, (b) signal, (c) idler, and (d) total 2 µm laser. The inset of (d) shows the far-field beam spot of the combined signal and idler.