Spatial coherence of fields from generalized sources in the Fresnel regime

TL;DR

This paper derives a closed-form approximation for the spatial coherence of partially coherent fields from generalized sources in the Fresnel regime, facilitating analysis and inverse scene reconstruction.

Contribution

It introduces a novel approximation formula for the coherence of generalized sources, extending the analysis beyond simple scenarios in the Fresnel regime.

Findings

Provides a closed-form approximation for coherence functions

Applicable to sources modulated by transmission functions

Enables inverse scene reconstruction from coherence measurements

Abstract

Analytic expressions of the spatial coherence of partially coherent fields propagating in the Fresnel regime in all but the simplest of scenarios are largely lacking and calculation of the Fresnel transform typically entails tedious numerical integration. Here, we provide a closed-form approximation formula for the case of a generalized source obtained by modulating the field produced by a Gauss-Shell source model with a piecewise constant transmission function, which may be used to model the field's interaction with objects and apertures. The formula characterizes the coherence function in terms of the coherence of the Gauss-Schell beam propagated in free space and a multiplicative term capturing the interaction with the transmission function. This approximation holds in the regime where the intensity width of the beam is much larger than the coherence width under mild assumptions on the modulating transmission function. The formula derived for generalized sources lays the foundation for the study of the inverse problem of scene reconstruction from coherence measurements.