Phase Retrieval using Nonlinear Curvature Sensing within Convergent Beams

TL;DR

This paper introduces a convergent-beam nonlinear curvature wavefront sensing method that enhances compactness and efficiency of adaptive optics systems by using a Fourier-transform-based reconstruction approach with multiple intensity measurements.

Contribution

It develops a practical physical optics model and a Fourier-transform-based reconstruction method for convergent-beam phase retrieval, improving compactness and performance of wavefront sensors.

Findings

Reduces size, weight, and complexity of wavefront sensors.

Validates the model through simulations and lab experiments.

Enables efficient wavefront reconstruction with convergent-beam measurements.

Abstract

Path-length diversity methods may be used for adaptive optics (AO) systems to retrieve phase and amplitude information by measuring intensity across multiple planes. Observations that rely on free-space propagation, such as the nonlinear curvature wavefront sensor (WFS), have been shown to offer excellent sensitivity and robustness to scintillation. However, the default design results in a large opto-mechanical footprint due to unavoidable geometric-optics and wave-optics effects. Measurements recorded in a convergent beam would improve instrument compactness, while concentrating light into smaller detector regions of interest, improving signal-to-noise ratio and possibly wavefront reconstruction speed. In this paper, we study path-length diversity wavefront sensing using four planes of contemporaneous intensity measurements made in a convergent beam. We develop a physical optics propagation model and validate the model by performing wavefront reconstructions in both simulations and lab experiments. The manuscripts core contribution is a practical, intensity-domain, Fourier-transform-based recipe to use a conventional multi-plane Gerchberg-Saxton (or comparable) reconstruction pipeline with convergent-beam measurements, enabling a compact optical layout. We find that this approach offers practical benefits over an equivalent free-space wavefront sensor, in particular reducing size, weight, complexity and cost.