Investigating the Limits of Hard X-ray Coherence Length Measurement Employing Young's Double Slit Experiment

TL;DR

This study assesses the limitations of Young's double slit experiment in measuring the spatial coherence of high emittance hard X-ray sources, revealing inherent ambiguities and proposing a new numerical method for source size estimation.

Contribution

It introduces a novel numerical technique for estimating source size from interference patterns and evaluates the fundamental limits of the double slit method for low coherence systems.

Findings

CLS has coherent beam properties with spatial coherence lengths up to 17.61 μm horizontally.

Vertical coherence lengths are at least three times larger than horizontal.

Theoretical analysis shows the inherent limitations of Young's double slit in characterizing diffraction-limited sources.

Abstract

Young's double slit experiment has been the most explored technique to gauge the coherence properties of a given system. The limits of this technique in characterizing spatial coherence properties of high emittance, hard x-ray synchrotron sources have been performed at the BXDS-IVU beamline, Canadian Light Source (CLS). High emittance synchrotron sources have always been assumed to possess sub-optimal coherence properties, especially in the hard X-ray regime. While this is largely true, it is very important to understand the limits of coherence for these existing high emittance sources. We have demonstrated that the Young's double slit experiment has harsher limits than what is normally expected in the form of inherent ambiguity. We present data obtained at multiple energies in both the horizontal and vertical direction leading to a thorough understanding of the fundamental limitations of employing Young's double slit experiment to characterize inherently low coherence length systems. We have put forth a novel numerical technique to estimate the source size directly from the Young's double slit interference patterns. With these results, we have demonstrated that CLS has functional coherent beam properties in the hard X-ray regime with Spatial coherence lengths ranging from 5.37$\mu \text{m}$ to 17.61$\mu \text{m}$ in the horizontal direction. The same in the vertical direction was at least 3 times larger. Finally, we present theoretical calculations showcasing the limits of Young's double slit experiment in characterizing diffraction limited sources.