Frequency doubling of twisted light independent of the integer topological charge

Light with orbital angular momentum (OAM), or twisted light, is widely investigated in the fields of optical communications, quantum information science, and nonlinear optics by harnessing its unbounded dimension. For nonlinear frequency conversion of twisted light, the efficiency usually decreases exponentially with increasing topological charge, which severely degrades the quality of the output modes. We here conceive and develop a method of eliminating the dependence of the conversion efficiency on the topological charge in second-harmonic generation using a single lens imaging technique. We first give the theoretical model and simulate the evolution of light beams near the image point of the lens, then the independence of the SHG conversion efficiency from topological charge is verified for different integer values of the topological charge; this independence is confirmed for varying pump power. The method can be generalized to other light–matter interactions and is a promising method of achieving higher efficiency and fidelity in the interaction of twisted light with matter.