Elongating the focal depth of a Bessel beam by manipulating polarization

The limits on the numerical aperture and diameter of optical elements restrict the propagation distance of a Bessel beam, resulting in finite depth of focus. In this paper, a method is proposed to elongate the focal depth by splicing a Bessel beam with a circular Airy beam, which is respectively excited by left- and right-circularly polarized light with a birefringent dielectric metasurface. Simulation shows that the focal depth of the spliced Bessel beam at the wavelength of 532 nm is 2.56 times that of the original. The lateral resolution satisfies the Rayleigh criterion, and the focal spot remains consistent. This scheme not only breaks the transmission distance limit of a Bessel beam but also provides an alternative way to extend the beam focal depth. This can be applied in micromachining and microscopic imaging.