Analytical solution for multisingular vortex Gaussian beams: The mathematical theory of scattering modes

TL;DR

This paper introduces a new analytical method using scattering modes and polynomial recurrence relations to solve the Schrödinger (paraxial wave) equation for multisingular vortex Gaussian beams, enabling explicit solutions for complex vortex configurations.

Contribution

The paper develops a novel analytical approach employing scattering modes and polynomial recurrences to solve multisingular vortex Gaussian beams, simplifying previous diffraction-based methods.

Findings

Derived recurrence relations for scattering mode polynomials.

Obtained closed-form solutions for multisingular vortex beams.

Simplified analysis of diffraction of high-charge vortices.

Abstract

We present a novel procedure to solve the Schr\"odinger equation, which in optics is the paraxial wave equation, with an initial multisingular vortex Gaussian beam. This initial condition has a number of singularities in a plane transversal to propagation embedded in a Gaussian beam. We use the scattering modes, which are solutions of the paraxial wave equation that can be combined straightforwardly to express the initial condition and therefore permit to solve the problem. To construct the scattering modes one needs to obtain a particular set of polynomials, which play an analogous role than Laguerre polynomials for Laguerre-Gaussian modes. We demonstrate here the recurrence relations needed to determine these polynomials. To stress the utility and strength of the method we solve first the problem of an initial Gaussian beam with two positive singularities and a negative one embedded in. We show that the solution permits one to obtain analytical expressions. These can used to obtain closed expressions for meaningful quantities, like the distance at which the positive and negative singularities merge, closing the loop of a vortex line. Furthermore, we present an example of calculation of an specific discrete-Gauss state, which is the solution of the diffraction of a Laguerre-Gauss state showing definite angular momentum (that is, a highly charged vortex) by a thin diffractive element showing certain discrete symmetry. We show that thereby this problem is solved in a much simpler way than using the previous procedure based in the integral Fresnel diffraction method.