Spatial interference of light: transverse coherence and the Alford and Gold effect

TL;DR

This paper investigates the interference of parallel Gaussian beams to measure spatial coherence length and observes an Alford-Gold-like effect in the transverse momentum domain, linking spatial and spectral interference phenomena.

Contribution

It introduces a method to determine spatial coherence length using beam separation interference and reports a novel observation of the Alford-Gold effect in the transverse momentum space.

Findings

Measured spatial coherence length of Gaussian beams.

Observed Alford-Gold effect in transverse momentum domain.

Linked spatial interference with spectral interference phenomena.

Abstract

We study the interference between two parallel-propagating Gaussian beams, originated from the same source, as their transverse separation is tuned. The interference pattern as a function of such separation lead us to determine the spatial coherence length of the original beam, in a similar way that a Michelson-Morley interferometer can be employed to measure the temporal coherence of a transform limited pulse. Moreover, performing a Fourier transform of the two-beam transverse plane, we observe an intensity modulation in the transverse momentum variable. This observation resembles the Alford and Gold Effect reported in time and frequency variables so far.