Fabrication of Fresnel zone plates for x-ray microscopy: diffractive optics for soft x-rays

Abstract

Fresnel zone plates are diffractive optical elements which are currently being used for high resolution x-ray microscopy. Several groups fabricate zone plates for use in specific microscopes [1] and we present here a summary on the fabrication of zone plates for use in the Scanning Transmission X-ray Microscope at the National Synchrotron Light Source. X-ray microscopy has demonstrated imaging with resolution five times superior to that which can routinely be achieved by visible light microscopy. In addition, x-rays with wavelengths between the carbon (4.2 nm) and oxygen (2.3 nm) K absorption edges are absorbed nearly an order of magnitude more strongly by organics than by water. This creates a natural absorption contrast mechanism and allows the viewing of many biological specimens wet and intact (without sectioning) and at atmospheric pressure [2]. By taking advantage of the spectroscopic properties of x-rays, x-ray microscopy can be used to map chemical elements and their binding states. Fluorescent chemical labels and gold labels can also be imaged at high resolution. Furthermore, several labs including ours are developing the capability to view radiation-tough frozen hydrated specimens in x-ray microscopes.