Method to measure off-axis displacements based on the analysis of the intensity distribution of a vortex beam

TL;DR

This paper presents a method to measure small off-axis displacements of Gaussian beams by analyzing the asymmetric diffraction patterns produced when crossing spiral phase plates, enabling high-precision beam alignment.

Contribution

The study introduces an analytical and numerical approach to relate diffraction pattern asymmetry to beam displacement, improving measurement accuracy for optical alignment.

Findings

Intensity ratio between peaks decreases exponentially with displacement

Higher singularity strength results in steeper decay of intensity ratio

Method allows high-precision detection of small beam misalignments

Abstract

We study the properties of the Fraunhofer diffraction patterns produced by Gaussian beams crossing spiral phase plates. We show, both analytically and numerically, that off-axis displacements of the input beam produce asymmetric diffraction patterns. The intensity profile along the direction of maximum asymmetry shows two different peaks. We find that the intensity ratio between these two peaks decreases exponentially with the off-axis displacement of the incident beam, the decay being steeper for higher strengths of the optical singularity of the spiral phase plate. We analyze how this intensity ratio can be used to measure small misalignments of the input beam with a very high precision.