Nonlinear orbital angular momentum conversion with spatial-amplitude independence

Nonlinear optics with structured light can provide a host of important functions for shaping the spatial and temporal structure of light, and the most commonly used is frequency conversion. In this work, we propose and demonstrate a novel nonlinear toolkit capable of tuning the frequency and orbital angular momentum (OAM) of signal beams simultaneously, and importantly that does not change the spatial amplitude structure of the signal. This unique frequency interface is enabled by using a special structured pump called a vortex super-Gaussian beam that has a flattop amplitude distribution and tunable vortex wavefront. This technique provides a dual interface of frequency and OAM, and may inspire many potential applications involving OAM beams.