# Quantitative orbital angular momentum measurement of perfect vortex beams

## TL;DR

This paper demonstrates a method to quantitatively measure the orbital angular momentum of perfect vortex beams, including superpositions, using hologram-based modal decomposition, which was previously thought unfeasible.

## Contribution

The authors develop and experimentally validate a technique for accurate OAM measurement of perfect vortices, enabling their use in advanced optical applications.

## Key findings

- OAM content of perfect vortices can be measured quantitatively.
- Superpositions of OAM within a single perfect vortex are detectable.
- Careful hologram design is essential for accurate modal decomposition.

## Abstract

Perfect (optical) vortices (PVs) have the mooted ability to encode orbital angular momentum (OAM) onto the field within a well-defined annular ring. Although this makes the near-field radial profile independent of OAM, the far-field radial profile nevertheless scales with OAM, forming a Bessel structure. A consequence of this is that quantitative measurement of PVs by modal decomposition has been thought to be unviable. Here, we show that the OAM content of a PV can be measured quantitatively, including superpositions of OAM within one perfect vortex. We outline the theory and confirm it by experiment with holograms written to spatial light modulators, highlighting the care required for accurate decomposition of the OAM content. Our work will be of interest to the large community who seek to use such structured light fields in various applications, including optical trapping and tweezing, and optical communication.