Switchable Gaussian and vortex beams via spot-defect control in an Nd:YAG oscillator and subsequent KTA-OPO

Tunable laser sources capable of controlling the spatial structure of light fields are of great significance for multimodal laser physics and structured beam studies. To achieve efficient and flexible mode switching, we for the first time, to the best of our knowledge, propose and demonstrate an electro-optic Q-switching Nd:YAG laser oscillator capable of switching between Gaussian and vortex beams through spot-defect modulation. By introducing a spot-defect on the surface of a quarter-wave plate and adjusting its rotation angle, rapid switching between Gaussian and vortex beams is realized within the stable Q-switching operation region, yielding pulse energies of 4.08 mJ and 4.10 mJ for the Gaussian and vortex beams, respectively, at a repetition rate of 1 kHz. Furthermore, when employed as the pump source for a KTiOAsO₄-based optical parametric oscillator (OPO), the system maintains consistent mode-switching behavior and excellent output performance in the mid-infrared region (∼3.5 µm).