Grazing angle Mach-Zehnder interferometer using reflective phase gratings and a polychromatic, un-collimated light source

Camille K Kemble,Julie Auxier,Nicole Y Morgan,Eric E Bennett,Han Wen,Susanna K Lynch

doi:10.1364/oe.18.027481

Abstract

Normal incidence Talbot-Lau interferometers in x-ray applications have the drawbacks of low fringe visibility with polychromatic sources when the wave propagation distance is increased to achieve higher phase sensitivity, and when fabrication limits the attainable grating density. In contrast, reflective gratings illuminated at grazing angles have dramatically higher effective densities than their physical values. However, new designs are needed for far field interferometers using grazing angle geometry with incoherent light sources. We show that, with the appropriate design and choice of reflective phase gratings, there exist pairs of interfering pathways of exactly equal lengths independent of the incoming beam's incidence angle and wavelength. With a visible light grazing angle Mach-Zehnder interferometer, we show the conditions for achieving near ideal fringe visibility and demonstrate both absolute and differential phase-contrast imaging. We also describe the design parameters of an x-ray interferometer and key factors for its implementation.

Highlights

Normal incidence, grating-based Talbot-Lau interferometers have a wide range of applications in matter-wave interference[1] and x-ray phase-contrast imaging[2]
We showed that grazing-angle Mach-Zehnder interferometers based on reflective phase gratings can produce interference fringes of near ideal visibility with white, un-collimated light sources
This method potentially overcomes the limitations in phase-contrast sensitivity of normal incidence Talbot-Lau interferometers, namely the need for monochromatic sources and difficulties in fabricating ultrahigh density gratings

Summary

Introduction

Normal incidence, grating-based Talbot-Lau interferometers have a wide range of applications in matter-wave interference[1] and x-ray phase-contrast imaging[2]. To achieve higher phase contrast sensitivity, both the density of the gratings and the order of the Talbot fringes need to be increased together. This in turn demands increasingly narrower linewidths of the light source. Since the phase contrast sensitivity scales with (grating period)/(propagation distance), higher sensitivity prefers wave propagation out to the far-field where chromatic dispersion becomes severe, and fringe visibility is further reduced. Talbot interferometers are less suitable for polychromatic light in the far-field range Another significant challenge in x-ray applications is the fabrication of dense gratings with periods below several microns, which requires structures of extremely high aspect ratios[5]

Methods

Results

Conclusion