Phase Zone Plates As Condensers For The Gottingen Scanning X-Ray Microscope

Abstract

With the Gottingen scanning x-ray microscope the synchrotron source is imaged by x-ray optics into a monochromatic small scan spot, through which a specimen can be moved. Hereby one part of the optics, the condenser zone plate and a pinhole, works as a linear monochro-mator in the wavelength region of λ= 2.36 nm to λ= 4.5 nm. The efficiency of such a condenser should be as high as possible to minimize the loss of radiation. Phase zone plates have a four times higher efficiency in the first order of diffraction than amplitude zone plates. Two condenser zone plates, KZP4 and KZP5, have been constructed so that they are well suited for the use in the scanning microscope. These zone plates have been made holo-graphically by superposing two wavefronts of laser light in an specific designed optical arrangement and exposing the zone plate structure into a photoresist. Using reactive ion etching (RIE) the structure has been transformed into Germanium. The thickness of the zone plate has been chosen to show at λ = 2.36 nm a phase effect. The efficiency has been measured at the Berliner Elektronenspeicherring Gesellschaft fUr Synchrotronstrahlung m.b.H., Berlin.