Generation of coherent superpositions of LG 0,±l modes with tunable topological charge in a Nd:YVO 4 microchip laser

The generation of a coherent superposition of LG 0,± l modes within a Nd:YVO 4 microchip laser pumped by a ring-shaped light based on a self-made annular aperture is reported. Numerical simulations are conducted on the threshold ratio of LG 0, l modes with adjacent topological charges. In the experiment, the focusing lens is adjusted axially to vary the size of the ring-shaped pumping light within the microchip crystal, enabling mode matching between the pumping light and LG 0, l modes of different topological charges. Ultimately, the coherent superposition of LG 0,± l modes with continuously tunable topological charges ranging from 7 to 19 is achieved. This approach offers the advantages of simplicity, compactness, and flexibility, as it does not necessitate the special design of the resonant cavity.