Reconfigurable generation of chiral optical fields with multiple selective degrees of freedom

Abstract

Chiral optical fields caused by vortex beams possessing orbital angular momentum (OAM) can be used to fabricate helically structured materials and identify chiral molecules, in which the materials or molecules are associated with the character of the irradiated light. However, previously reported chiral optical fields can control only some of the parameters including the number of fringes, size, ellipticity, orientation, and local intensity distribution, which may hamper their applications. Thus, in this work, we propose both theoretically and experimentally an approach to fabricate chiral optical fields with five separately controllable degrees of freedom by overlapping two anisotropic vortices whose wavefronts have a nonlinear phase variation with the azimuthal angle. The local intensity distribution, number of fringes, size, orientation, and ellipticity of the chiral optical field can be dynamically controlled by adjusting the nonlinear coefficient, topological charges, axicon parameter, rotation angle, and stretching factor of the anisotropic vortices. Furthermore, the OAM density was investigated and proven to be continuously enhanced with the variation of the field’s local intensity distribution, which gives the proposed approach the ability to continuously manipulate the OAM density of chiral optical fields. This work, supporting chiral optical fields by five separately controllable parameters, may make the applications of chiral optical fields in the fields of nanostructure fabrication and optical tweezers more flexible.