Optical vortex pumped mid-infrared optical parametric oscillator.

The first demonstration of a mid-infrared optical parametric oscillator pumped by 1-μm optical vortex pulses is presented. A 0.5-mJ 2-μm fractional vortex pulse having half-integer topological charge is generated. Using this system, 0.24-mJ vortex pulses with a topological charge of 1 can be created. The topological charges of the mid-infrared vortex pulses are observed by an interferometric technique in combination with second-harmonic frequency conversion.