Multi-Spiral Laser Patterning of Azopolymer Thin Films for Generation of Orbital Angular Momentum Light

Abstract

Recently, the realization of the spiral mass transfer of matter has attracted the attention of many researchers. Nano- and microstructures fabricated with such mass transfer can be used for the generation of light with non-zero orbital angular momentum (OAM) or the sensing of chiral molecules. In the case of metals and semiconductors, the chirality of formed spiral-shaped microstructures depends on the topological charge (TC) of the illuminating optical vortex (OV) beam. The situation is quite different with polarization-sensitive materials such as azopolymers, azobenzene-containing polymers. Azopolymers show polarization-sensitive mass transfer both at the meso and macro levels and have huge potential in diffractive optics and photonics. Previously, only one-spiral patterns formed in thin azopolymer films using circularly polarized OV beams and double-spiral patterns formed using linearly polarized OV beams have been demonstrated. In these cases, the TC of the used OV beams did not affect the number of formed spirals. In this study, we propose to use two-beam (an OV and a Gaussian beam with a spherical wavefront) interference lithography for realization spiral mass transfer with the desired number of formed spirals. The TC of the OV beam allows for controlling the number of formed spirals. We show the microstructures fabricated by the laser processing of thin azopolymer films can be used for the generation of OAM light at the microscale with the desired TC. The experimentally obtained results are in good agreement with the numerically obtained results and demonstrate the potential of the use of such techniques for the laser material processing of polarization-sensitive materials.

Vectorial spin-orbital Hall effect of light upon tight focusing and its experimental observation in azopolymer films

“…The profiles of the fabricated microstructures coincides well with the distributions of which actually corresponds to the inversion of the intensity of the longitudinal component. Previously, these distributions have shown good agreements with the three-dimensional profiles of microreliefs formed in thin azopolymer films when they were illuminated by linearly and circularly polarized vortex beams 33 , high-order cylindrical beams and their combinations 32 , and interferometrically shaped multi-spiral circularly polarized laser fields 34 . We can conclude that these experimentally obtained results are in good agreement with numerically obtained ones and clearly indicate the vectorial spin-orbital Hall effect of light upon focusing.…”

“…In particular, the x-component coincides with the y-component from Section Linear x-polarization of the input field (see Eqs. (32,33)), and the focal intensity distribution for the y-component depends only on the input field displacement in the horizontal direction α 0 :…”

Generation of Orbital Angular Momentum Light by Patterning Azopolymer Thin Films

“…When the laser beam passes through the azobenzene film, the molecules of the azobenzene interacts with the laser light by changing their orientation, depending on the orientation and polarization of the light. The interferometric technique or the use of spiral phase plate detects and measures the presence and value of the OAM mode imprinted in the beam, after it interacts with thee azobenzene molecules [134]. This research describes how multi-spiral microstructures are generated by an interferometric approach in azopolymer thin films in the Mach−Zehnder interferometer.…”