Adjustable near-field chirality of optical vortex beams using the spheroidal particles

Enhancement and adjustment for the chirality of optical vortex beams has become a research hotspot and attracted considerable attention in recent years. Using the simple and low-cost dielectric microparticles is expected to realize this target. In this work, we report an investigation into the adjustable near-field chirality of optical vortex beams via the spheroidal particles by using the finite-difference time-domain (FDTD) method. Based on the vector potential method, the explicit analytical expressions for the electric and magnetic field components of the Laguerre-Gaussian (LG) vortex beams are derived and implemented into the FDTD method. The chirality density distributions of the electromagnetic fields near the spheroidal particles under the illumination of LG vortex beams are calculated and discussed. The results show that the chirality of optical vortex beams can be flexibly adjusted by altering the refractive index and ellipticity of the dielectric spheroidal particles. This work provides an alternative approach to control the near-field chirality of optical vortex beams and has potential applications in chiral recognition, detection, and manipulation.