Achievement of tunable vortex beams with dual index by intra-cavity multi-surface construction modulation

Tunable vortex beams with dual index and high power potential have been widely applied in various fields. However, due to the trade-off between the adjustment flexibility and the power damage threshold of the adopted elements, the generation of tunable vortex beams with dual index and high power potential remains a challenge. The deformable mirror (DM) with high power damage threshold and flexible adjustment ability, has the potential for generating vortex beams with the capability to high power, but vortex beams with only single index have been realized. Herein, the method based on intra-cavity multi-surface construction modulation with DM and extra-cavity conversion, is first proposed to generate tunable vortex beams with dual index. The vortex beams could be achieved by extra-cavity conversion of the Hermite-Gaussian (HG) beams generated from a resonant cavity. In this work, a designed Z-shaped resonant cavity is used, and the modulation conditions for generating HG beams and vortex beams with dual index are investigated based on four classic surface construction methods. The dual single piezoelectric (PZT) DM with a simple manufacturing process and low manufacturing cost, is adopted and has been proven to generate tunable HG beams and vortex beams with dual index. For the adopted dual single-PZT modulation method, the influence of parameters (i.e., cavity structure parameters, DM assembly parameters and DM structure parameters) on the generated laser beams have been further investigated in simulation to ensure the selection of suitable parameters. The experiment has been conducted and the experimental results have been proven the feasibility of the proposed method, which is of great significance for generating tunable vortex beams with dual index in various applications.