FFFI: A Full-Field X-ray Fluorescence Imaging System

A full field X-ray fluorescence imaging system requires two major subsystems: an optical system which provides suitable magnification of the emissions to provide the required spatial resolution while remaining achromatic, and a detector capable of spectral resolution in each pixel. In this work, we will present two examples of full-field imaging optics that satisfy this requirement. The first is a tapered polycapillary optic, the second is a Modified Uniform Redundant Array (MURA) coded aperture. Polycapillary optics have the advantage of giving direct imaging of a sample but are not strictly achromatic. We will show fluorescence slice tomography data from samples using a tapered polycapillary optic with a 5:1 taper. MURAs use the concept of coded aperture arrays which have the attraction of having higher efficiency with 50% open area. Our arrays have 7 µm openings and are truly achromatic in our energy regime (2-14 keV) but require computation to form an image. Using our silicon laboratory at Brookhaven National Laboratory we have produced various orders of MURAs made from gold on a 1 µm thick silicon nitride membrane. A custom detector is being designed for this project. That design is being presented separately at this conference. It will offer 128 x 128 pixels, each 100 µm square, and will provide spectra with around 200eV resolution at 5.9keV. Readout will be sparsified to minimize the required readout bandwidth.