T.V.S. Pillai

Generation of a strong uniform transversely polarized nondiffracting beam using a high-numerical-aperture lens axicon with a binary phase mask

We present a theoretical approach to generate a nondiffracting beam with extended depth of focus (DOF) and a smaller focal spot along the optical axis, by tight focusing of an azimuthally polarized beam with a circular symmetrical binary phase mask and an interference effect over a high-numerical-aperture (NA) lens axicon system. We find a general azimuthal diffraction integral for the circularly symmetric binary phase mask and examine it in two special cases: a high-NA lens and a high-NA lens axicon. The azimuthally polarized beam remains well behaved in both cases. We verify that the longitudinal component generated by azimuthally polarized illumination produces the narrowest spot size for a wide range of geometries. Finally, we discuss the effects of tight focusing on a dielectric interface and provide some ideas for circumventing the effects of the binary phase mask interface and even utilize them for spot size reduction.

Tight Focusing Properties of Radially Polarized Gaussian Beams with Pair of Vortices

The tight focusing properties of a radially polarized Gaussian beam with a nested pair of vortices having a radial wave front distribution are investigated theoretically by the vector diffraction theory. The results show that the optical intensity in the focal region can be altered considerably by changing the location of the vortices nested in a radially polarized Gaussian beam. It is noted that focal evolution from one annular focal pattern to a highly confined focal spot in the transverse direction is observed corresponding to the change in the location of the optical vortices in the input plane. It is also observed that the generated focal hole or spot lead to a focal shift along the optical axis remarkably under proper radial phase modulation. Hence the proposed system may be applied to construct tunable optical traps for both high and low refractive index particles.

Generation of tunable focal holes by tight focusing of phase modulated azimuthally polarized double ring shaped beam

We investigated the focusing properties of a double ring shaped azimuthally polarized beam using a high NA lens and a dedicated binary phase filter. The definition of azimuthally polarized double ring beam is stated, and proposed with phase filter. The results have been presented for total intensity distribution and squares of the polarization components at the focal plane of a high numerical aperture system, for values of the topological charge. Focusing beam results in the stretching of the intensity pattern as well as of the squares of the polarization components. We observe that by using 3 belts and 5 belts binary phase filters novel focal patterns including multiple ring structures and focal splitting are obtained. this kind of system is worthwhile for manipulation of nano particles, trapping and for building nano structures for NEMS applications.