Frequency conversion of orbital angular momentum with optimized efficiency and modal purity

The use of nonlinear optics for the creation, control, and detection of structured light has gained prominence of late, but it is plagued by low efficiency and variable modal purity. Here, we show how to optimize the efficiency and modal purity in the nonlinear conversion of structured light modes. Using difference frequency generation of orbital angular momentum carrying Laguerre–Gaussian modes as an example, we achieved more than a 40% rise in efficiency while maintaining the modal purity above 90% compared to conventional methods. To demonstrate the versatility of our approach, we show the frequency conversion of perfect vortex beams up to ℓ =40 in a topological charge, achieving a new state of the art. We believe this theoretical treatment will facilitate our work’s translation to other modal forms and nonlinear processes.