OAM-controlled transfer and mid-infrared vortex generation (>4 μm) in a signal-singly resonant ZGP OPO

We demonstrated selective transfer of orbital angular momentum (OAM) to either the signal or idler in a noncollinear, signal-singly resonant ZGP optical parametric oscillator (OPO) pumped by a 2.05 μm vortex beam. By tuning the cavity length, both signal and idler vortices reached output energies above 1 mJ, whereas under collinear pumping the OAM was invariably transferred to the idler. For short cavities (50-70 mm), selective OAM transfer could also be achieved by adjusting the pump-beam tilt, enabling flexible active OAM control. Due to intrinsic instability and poor mode discrimination, the mid-infrared vortex beam quality in the plane-parallel cavity deteriorated. To overcome this, we implemented a four-mirror ring-cavity ZGP OPO, generating a ∼1 mJ first-order vortex idler at 4.45 μm with <i>M</i>² factors close to 2, an optical-to-optical conversion efficiency (OOCE) exceeding 16%, and tunability from 4.3 to 5 μm.