Incoherent imaging with the soft X-ray microscope

摘要

The imaging characteristics for X-raywavelengths in the "water window" under incoherent imagingconditions (large detector aperture) are examined for the King'sCollege London scanning transmission X-ray microscope withzone-plate objective installed at the Daresbury (UK)synchrotron. The principal consideration was to express imagetheory, incorporating wave aberrations and apodised zone plates,and to apply the theory to experimental data. Comparisons aremade, showing reasonable agreement, for a range of defocusvalues and two wavelengths. Due to problems in fabrication itwas necessary to determine the effective, or operational, zone-plate parameters (radius of outermost active zone r_N, width ofoutermost active zone dr_N); this was accomplished by through-focus series. Calculated point spread functions were used todeblurr images, in through-focus series of two-dimensionalscanned X-ray images of specimen holes and test gratingpatterns. Significant contrast enhancement is achieved afterdeconvolution with a best point-to-point resolution of about 35 nm.