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Investigation of Properties of Nonlinear Spiral Phase Plates

We numerically and experimentally investigate the properties of nonlinear spiral phase plates (SPPs) with the transmission function exp(imφn). In contrast to conventional SPPs, nonlinear SPPs can be used for the generation of vortex non-ring light distributions in the form of light spirals. We study the generation of such laser beams both in the paraxial approximation and under the sharp focusing conditions and demonstrate the transformations arising in the focal plane. The orbital angular momentum density distribution of the generated light distributions is non-uniform that can be useful for optical tweezers applications and for investigation of laser-matter interaction in the case of azopolymers that are sensitive to the polarization state of the incident light.