A V-Folded Digital Laser for On-Demand Vortex Beams by Astigmatic Transformation of Hermite–Gaussian Modes**Supported by the National Natural Science Foundation of China under Grant Nos 61605049 and 61575070, and the Natural Science Foundation of Fujian Province of China under Grant No 2018J01003, the Fundamental Research Funds for the Central Universities under Grant No ZQN-707, and the Subsidized Project for Postgraduates’

Abstract

A V-folded digital laser using a spatial light modulator (SLM) for intra-cavity loss shaping is exploited to generate Hermite–Gaussian modes with on-demand mode order. With a π/2 astigmatic mode converter, vortex beams carrying on-demand orbital angular momentum (OAM) with a tunable range from −11ħ to 12ħ are obtained. The mode order of the HG mode, hence the OAM of the vortex beam, is digitally switched by changing the phase pattern imposed on the SLM without requiring any mechanic alignment of the cavity. This work has great potential applications in various OAM-tunable vortex beams.