X-ray microscopy in the water window

The development of multilayer coatings which permit the efficient reflection of X-rays within a narrow wavelength band at normal or near-normal angles of incidence has resulted in the fabrication of X-ray telescopes and microscopes which have distinct advantages compared to their grazing incidence counterparts. These advantages include superior angular resolution and the ability to select a narrow X-ray band for imaging while rejecting radiation outside this band. The application of this technology to astronomical telescopes for the study of the sun is reviewed, and a development program for its application to biological microscopes able to operate in the important water window, between the K absorption edges of oxygen (23.3 AA) and carbon (43.68 AA), is described. The design and analysis effort discussed has established that the Schwarzschild configuration affords a feasible approach for an imaging X-ray microscope operating in the water window.<>