Diffractive optical elements for differential interference contrast x-ray microscopy

Enzo Di Fabrizio,Jean Susini,Thomas Wilhein,Dan Cojoc,Paolo Facci,Stefano Cabrini,Burkhard Kaulich

doi:10.1364/oe.11.002278

Abstract

In this paper we introduce phase diffractive optical elements (DOEs) that beside simple focusing, can perform new optical functions in the range of x-rays. In particular, the intensity of the wavefront can be distributed with almost complete freedom. We calculated and fabricated high resolution DOEs that can focus a monochromatic x-ray beam into multiple spots displaced in a single or two planes along the optical axis or can shape the beam into a desired continuous geometrical pattern. The possibility to introduce a specified phase shift between the generated spots, which can increase the image contrast, is demonstrated by preliminary results obtained from computer simulations and experiments performed in visible light. The functionality of the DOEs has been tested successfully in full-field differential interference contrast (DIC) x-ray microscopy at the ID21 beamline of the European Synchrotron Radiation Facility (ESRF) operated at 4 keV photon energy.

Highlights

In the last decade there is an increased interest for extreme violet and x-ray microscopy
In this paper we extend the concept of zone plates (ZPs) to a more general category of diffractive optical elements (DOEs) that can accomplish optical functions specific to differential interference contrast (DIC) microscopy and general beam shaping
The extension to x-rays range was first approached in view of projection x-ray lithography [13] and the implementation of a DOE that generated a dotted pattern is reported in reference [14]

Summary

Introduction

In the last decade there is an increased interest for extreme violet and x-ray microscopy This is due to the characteristics of the beam that can be obtained in the third generation synchrotron radiation sources [1]: high brightness, low divergence and an almost monochromatic spectrum for an energy that can be tuned over a range of several keV. When a source of electromagnetic radiation is bright enough (i.e., point-like and monochromatic) new worlds open up for the designer of optical instruments and for a wider community of experimenters and theorists. This happened with the invention of the optical microscope and is still happening with x-ray microscopes of the latest generation [2,3]. We show the possibility to introduce a specified phase shift between the generated spots, which can be useful to increase the image contrast, and we demonstrate it by preliminary results obtained from computer simulations and experiments performed in visible light

Bias retardation in DIC microscopy

Design of DOE for beam shearing in DIC

DOE fabrication for x-ray DIC microscopy

DIC x-ray microscopy experiments in the full field image setup

Findings

Conclusions