We investigated the shear interferograms that are produced by superpositions of two vortex beams. When the ratio of the amplitudes of the vortex modes is not too dissimilar (ratio less than 0.6 or greater than 1.7) the interferograms contain an array of vortex signatures that can be decoded. The signature of a vortex in shear interferograms consists of linked forks that reveal the sign and magnitude of the topological charge of the vortex. The distribution of vortices in a superposition of two modes is related to the topological charges of the component modes. Thus, the shear pattern of a composite mode can be deciphered to obtain the topological charge of the component beams and their relative amplitude. This method works for diffracting beams such as Laguerre-Gauss (of radial order zero) and other similar types of modes, such as hypergeometric-Gaussian beams.
The topological charge (l) is the parameter that defines the amount of orbital angular momentum (OAM) of beams carrying optical vortices. In this article we expand on a robust experimental method to determine the topological charge that we previously developed [B. Khajavi & E. J .Galvez, Opt. Lett. 42, 1516-1519 (2017)]. This method consist of using a pair of confocal lenses and a wedged optical flat as a shearing interferometer. The interference pattern produced by a pure OAM mode directly reveals the magnitude and sign of the topological charge: two conjoined forks with |l| + 1 number of tines pointing away from (towards) one another for l > 0 (l < 0). Superpositions of two modes with the same value of |l| but with the opposite sign produce shearing interference patterns that can be used the infer the value of l and the relative weight of the component modes.
We investigate disclinations in the orientation of space-variant polarization patterns produced by collinear non-factorizable superpositions of high-order spatial modes and polarization. Asymmetric disclination patterns were formed by superpositions of spatial modes with asymmetric optical vortices. They give rise to monstar patterns of high order that can have a negative or positive disclination index. This has led to an examination of what constitutes a monstar. We present theoretical as well as experimental results.
We investigate a force that has been predicted to discriminate molecules by their chirality when they are in the presence of an optical field with a polarization-helicity gradient. We investigate several experimental geometries for observing evidence of this force via enantiometer separation in racemic mixtures. We do this with singular-optical beams carrying a polarization helicity gradient across their transverse mode. Molecular diffusion and the dipole force – an intensity-gradient force – have so far precluded measurements of this force.
We present modelings of high-order line singularities encoded in space-variant polarization of light. This involves calculating the line patterns produced by the superposition of light beams in orthogonal states of circular polarization, with each beam carrying an optical vortex, and where one of them is asymmetric. This setting allowed us to study the case of monstars of high order. We find that monstars can have positive or negative singularity indices, modifying the previous understanding of the pattern, which was based on the case of lowest-order C- points. Monstars then remain characterized only by their own unique feature: sectors with patterns of mostly curved lines that radiate from the center. Given this definition, we propose that the case where the index is +1 be classified as a monstar. We also found that the asymmetric modes contain kinks that appear in the C-lines of a distinct but related pattern that contains line orientation discontinuities.
We present a same-path polarization interferometer that uses two spatial light modulators to encode the most general type of Poincaré beam. We demonstrate this design by presenting new results on the encoding of symmetric C-point polarization singularities using spatial modes with high-order topological charges. We also present new results on composite C-points. These are cases where there are multiple C-points in a single beam obtained by combining two modes with composite optical vortices in orthogonal states of polarization. The measurements show good agreement with the simulations.
We prepare heralded single photons in a non-separable superposition of polarization and spatial modes using an in-beam polarization interferometer enabled by a spatial light modulator. We diagnose the quantum state using two techniques: quantum state tomography and imaging polarimetry. The results are in very good agreement with the expectations.
We present analysis and measurements of the polarization patterns produced by non-collinear superpositions of Laguerre-Gauss spatial modes in orthogonal polarization states, which are known as Poincaré modes. Our findings agree with predictions (I. Freund Opt. Lett. 35, 148-150 (2010)), that superpositions containing a C-point lead to a rotation of the polarization ellipse in 3-dimensions. Here we do imaging polarimetry of superpositions of first- and zero-order spatial modes at relative beam angles of 0-4 arcmin. We find Poincaré-type polarization patterns showing fringes in polarization orientation, but which preserve the polarization-singularity index for all three cases of C-points: lemons, stars and monstars.