Project of Transmission X-ray Microscope-Interferometer for 15-35 keV Synchrotron Radiation
A new Transmission X-ray Microscope-Interferometer, which is based on X-ray refractive lenses and diffractive gratings, was developed for 15-35 keV photon energies in order to create the X-ray optics at the Siberian Center of Synchrotron an Terahertz Radiation and to set up the TXMI at the front-end #2 of storage ring VEPP-4M. Unlike with diffractive zone plates, which are applied at present as objectives in modern X-ray microscopes, there is no a requirement of a high spatial transverse coherence for X-ray refractive lenses. In case of zone plate, the coherence should be comparable with 50-100 microns of a zone plate diameter, that leads to a pure photon flux at the object plane and, respectively, to a necessity of its cryogenic treatment of a specimen and its fixation at vacuum conditions. X-ray refractive optics enable to use hard X-rays, providing X-ray microscopy imaging at air environment and with low radiation damages. In order to increase sensitivity of the X-ray microscopy phase contrast imaging of the objects, which have homogeneous X-ray absorption or transparency (for an example, living biological cells in their habitat, i.e. in the open air, in a water solution), the X-ray interferometric gratings are set nearby the object zone. The local coherent zone for the interferometric gratings is formed by means of special X-ray refractive condenser lens with a long-length focal waist. The intensity changes of moiré phone function from X-ray gratings because of X-ray phase structural heterogeneities of the micro objects are revealed typically by computed analysis of the X-ray microscopic image. Previous result  of computed X-ray phase contrast tomography using X-ray amplitude and phase gratings in the geometry of Talbot interferometer have demonstrated X-ray imaging visibility of internal structure of biological object with homogeneous X-ray absorption and phase structural non-uniformity with extremely low changes of X-ray refraction index decrement. And also, X-ray imaging of micro objects by means of a transmission X-ray microscope based on X-ray refractive objective and condenser lenses have been demonstrated previously  with spatial resolution up to tens of nanometers using monochromatic synchrotron radiation of 15-30 keV photon energies. The scientific novelty of the project is the combination of X-ray microscopy based on X-ray refractive long lenses for hard X-rays with X-ray interferometry and using X-ray gratings in the local coherence zone, which is formed by X-ray refractive condenser. In the paper, we describe the operations flowchart of the TXMI in detail. The block sequence on the SR beam course is the following: 1) A forvacuum chamber includes horizontal and vertical slits, a multilayered X-ray mirror-monochromator, a detector of the SR beam position and a blocker absorbing the direct beam. 2) The block of the X-ray refractive condenser lens has the air atmosphere. 3) Further, a forvacuum tube for the beam inflight after the condenser. 4) The block of a research object and the X-ray refractive objective lens with X-ray diffractive gratings is in the air environment. 5) Further, a forvacuum tube for the beam inflight after the objective lens. 6) The air block of the TXMI detector is disposed at the end of the beamline station. It includes an X-ray scintillator and an optical microscope with a planapochromate objective, inclined mirror and digital camera.
 G. Schulz, T. Weitkamp, I. Zanette, F. Pfeiffer, F. Beckmann, Ch. David, S. Rutishauser, E. Reznikova, B. Mueller. High-resolution tomographic imaging of a human cerebellum: Comparison of absorption and grating based phase contrast. Journal of the Royal Society Interface, 7 (2010) 1665 – 1676. doi:10.1098/rsif.2010.0281.  E. Reznikova, T. Weitkamp, V. Nazmov, A. Last, M. Simon, V. Saile. Transmission hard X-ray microscope with increased view field using planar refractive objectives and condensers made of SU-8 polymer. J. Phys.: Conf. Ser. 186, 012070 (2009).