Position measurement of non-integer OAM beams with structurally invariant propagation

TL;DR

This paper introduces a method to generate non-integer OAM beams with fixed symmetry axes, enabling simplified position measurement and analysis of how OAM and mode orientation affect detector response.

Contribution

The work presents a novel design for structurally invariant non-integer OAM beams with fixed symmetry axes, improving calibration and understanding of detector responses.

Findings

Quadrant detector response depends on OAM and mode orientation.

Symmetry axes of the beams remain fixed despite OAM variation.

Analytical and experimental validation of the detection method.

Abstract

We present a design to generate structurally propagation invariant light beams carrying non-integer orbital angular momentum (OAM) using Hermite-Laguerre-Gaussian (HLG) modes. Different from previous techniques, the symmetry axes of our beams are fixed when varying the OAM; this simplifies the calibration technique for beam positional measurement using a quadrant detector. We have also demonstrated analytically and experimentally that both the OAM value and the HLG mode orientation play an important role in the quadrant detector response. The assumption that a quadrant detector is most sensitive at the beam center does not always hold for anisotropic beam profiles, such as HLG beams.