Speckles generated by skewed, short-coherence light beams

TL;DR

This paper introduces a novel method using skewed coherence beams to generate speckles with short-coherence light, enabling heterodyne detection and suppression of multiple scattering in turbid samples, with potential applications in X-ray imaging.

Contribution

The study demonstrates that skewed coherence beams can produce speckles and enable heterodyne detection despite short coherence, expanding applications in scattering and X-ray imaging.

Findings

Skewed coherence beams generate speckles with short coherence.

The technique suppresses multiple scattering in turbid samples.

Potential for heterodyne detection with standard short-coherence sources.

Abstract

When a coherent laser beam impinges on a random sample (e.g. a colloidal suspension), the scattered light exhibits characteristic speckles. If the temporal coherence of the light source is too short, then the speckles disappear, along with the possibility of performing homodyne or heterodyne scattering detection or photon correlation spectroscopy. Here we investigate the scattering of a so-called "skewed coherence beam", i.e., a short-coherence beam modified such that the field is coherent within slabs that are skewed with respect to the wave fronts. We show that such a beam generates speckles and can be used for heterodyne scattering detection, despite its short temporal coherence. When applied to quite turbid samples, the technique has the remarkable advantage of suppressing the multiple scattering contribution of the scattering signal. The phenomenon presented here represents a very effective method for measuring the coherence skewness of either a continuous wave or a pulsed beam. Another field of application concerns X-rays. The observation of speckles is usually limited to synchrotron radiation and FELs. Our experiment suggests that a short-coherence X-ray source can also be used, with no monochromator filtration, provided that the coherence is suitably skewed. Such a technique will also enable heterodyne scattering detection with standard short-coherence light sources.