Direct generation of radial-index-tunable Laguerre-Gaussian modes from a Janus laser

Compact lasers capable of directly generating highly pure Laguerre-Gaussian (LG) modes can serve as reliable structured light sources for diverse applications including optical communications, precision measurement, optical imaging, holography, and quantum information processing. However, manipulating the radial index of the LG modes inside the laser remains a significant challenge. Here, we experimentally demonstrate the generation of LG modes (l = 5) with tunable radial-index (from p = 5 to p = 9) from a Janus laser by using a single geometric phase plate (GPP) inside the cavity. The tunable output mode is achieved by simply altering the axial position of the intracavity lens. The mode purities are all above 90%. In addition, the superimposed LG modes can be obtained through properly positioning the intracavity lens. Our work paves a useful way to manipulate the radial index of a high-purity LG-mode laser for advanced applications in optical measurements, optical communications, and quantum entanglements.