Fig. 1. Experimental schematic of an idler-resonant optical vortex parametric oscillator based on KTA

Fig. 2. Spatial forms and interference fringes of pump vortex beam, signal output and idler output. (a)(b) Spatial form and interference fringes of the pump vortex beam; spatial forms and interference fringes of the signal output (c)(d) and idler output (e)(f) for a plane-parallel cavity; spatial forms and interference fringes of the signal output (g)(h) and idler output (i)(j) for a plane-concave cavity

Fig. 3. Spectra of the signal and idler outputs at the wavelength of 1.535 μm and 3.468 μm, respectively. The insets show the spectrum bandwidth of the signal and idler outputs

Fig. 4. Beam quality factor (M ²) of the idler output

Fig. 5. Plot of the output energies of the signal and idler outputs as a function of the pump energy in a plane-parallel cavity and a plane-concave cavity