Separation and interference of polarization in radially polarized Laguerre-Gaussian beams

The angular momentum properties of light can be described mathematically in terms of a higher-order Poincaré ball. The superposition of spin angular momentum (SAM) and orbital angular momentum (OAM) quantum states produces novel laser beams with unique spatial structures, which have great potential for applications in microscopic imaging, optical manipulation, and materials processing. Currently, researchers have developed a variety of techniques for preparing and controlling structured beams. In this study, a novel all-solid-state semiconductor side-pumped laser is introduced, which utilizes a thermal lens to image chromatic aberration, which is different from conventional chromatic aberration, a phenomenon that originates from the difference in the magnitude of the refractive indices tangentially and radially polarized light in the side-pumped Nd:YAG crystals, wherein the radial polarization is thermally less focalized as compared to the azimuthal polarization, thus enabling a stable mode selection through spherical aberration. Mode selection through spherical aberration is achieved by directly synthesizing a stable Laguerre-Gaussian (LG) radially polarized beam in a resonant cavity. The theoretical analysis explores the superposition states of two beams, LG ⁺ ₀₁ and LG^-₀₁, with opposite topological charges, and the effect of the hot lens position on the output beam characteristics. In the experiments, we designed a semiconductor transversely pumped Nd:YAG laser. The obtained radially polarized Laguerre-Gaussian beams are formed by the superposition of circularly polarized vortex beams of opposite chirality. The circularly polarized vortex beams with opposite chiralities are separated by a separation device, and then interference experiments are performed separately to observe the interference patterns with obvious bifurcations and verify the theoretical analysis. The proposed method provides a direct and simple way to generate structured laser beams.