Identifying the tilt angle and correcting the orbital angular momentum spectrum dispersion of misaligned light beam

TL;DR

This paper presents a two-step method to identify and correct the tilt-induced dispersion in the orbital angular momentum spectrum of misaligned light beams, enhancing measurement accuracy in optical systems.

Contribution

It introduces a novel approach to measure tilt angles precisely and correct OAM spectrum dispersion without requiring perfect axis alignment.

Findings

Tilt angle measured with 10^-4 rad precision

Successful correction of OAM spectrum dispersion

Effective for both pure and superposed OAM states

Abstract

The axis tilt of light beam in optical system would introduce the dispersion of orbital angular momentum (OAM) spectrum. To deal with it, a two-step method is proposed and demonstrated. First, the tilt angle of optical axis is identified with a deduced relation between the tilt angle and the variation of OAM topological charges with different reference axes, which is obtained with the help of a charge coupled device (CCD) camera. In our experiments, the precision of measured tilt angle is about 10-4rad with OAM orders of -3~3. Using the measured angle value, the additional phase delay due to axis tilt can be calculated so that the dispersion of OAM spectrum can be corrected with a simple formula while the optical axis is not aligned. The experimental results indicate that the original OAM spectrum has been successfully extracted for not only the pure OAM state but also the superposed OAM states.