Nondiffracting transversally polarized beam

Abstract

Generation of a nondiffracting transversally polarized beam by means of transmitting an azimuthally polarized beam through a multibelt spiral phase hologram and then highly focusing by a high-NA lens is presented. A relatively long depth of focus (∼4.84λ) of the electric field with only radial and azimuthal components is achieved. The polarization of the wavefront near the focal plane is analyzed in detail by calculating the Stokes polarization parameters. It is found that the polarization is spatially varying and entirely transversally polarized, and the polarization singularity disappears at the beam center, which makes the central bright channel possible.

Creation of super-long bright channel using high NA lens axicon with dedicated multibelt binary phase mask

“…Generally a double-ring-shaped azimuthally polarized beam without any phase modulation is tightly focused, a single-ring focal hole pattern is obtained (Lalithambigai et al 2013). It is reported that using SPM with a high NA lens one can generate a single transversely polarized bright focal spot (Yuan et al 2011). Hence, in order to generate bright spot in the focal region, we need an SPM with a high NA lens system.…”

“…However, it is also confirmed that the azimuthally polarized beam phase encoded by a vortex 0-2π phase would produce a considerably sharper focal spot on the focal region (Hao et al 2010). More recently, the generation of a non diffracting transversally polarized beam have the long DOF (4.84 λ) with sub diffraction spot size (0.53 λ) by highly focusing an azimuthally polarized beam with a high NA lens and a multibelt spiral phase hologram is established numerically (Yuan et al 2011). Another study, a subwavelength transversally polarized beam have the spot size (0.384 λ) with a longer DOF (over 11.454 λ) has been generated using high NA lens axicon with multibelt phase modulation (Suresh et al 2013).…”

“…The total electric field in the focal region under phase-modulated azimuthally polarized beam illumination can be obtained in cylindrical coordinates as (Yuan et al 2011;Suresh et al 2013;Lalithambigai et al 2014),…”

“…Usually azimuthally polarized beam generates a dark hollow intensity ring in the focal region and the total intensity represents only the azimuthal component E φ . But, it is reported that using a SPM and a high NA lens system one can generates a single transversely polarized bright focal spot by azimuthally polarized beam (Yuan et al 2011). Hence, in order to generate bright spot in the focal region, we need a SPM with high NA lens system.…”

Tight focus of light using micropolarizer and microlens

“…By replacing the 532-nm incident wavelength with λ = 633 nm, we managed to obtain [11] a tighter focal spot of size FWHM = (0.40 ± 0.02)λ using the same microlens. Publications concerned with the subwavelength focusing of radially and azimuthally polarized laser beams have also been widely known [12][13][14][15]. Focal spots of size FWHM = 0.43λ (NA = 0.95) [12,14], FWHM = 0.30λ (NA = 1.4) [13] have been obtained in the numerical and physical experiments.…”