Near, far, wherever you are: simulations on the dose efficiency of holographic and ptychographic coherent imaging

Different studies in x-ray microscopy have arrived at conflicting conclusions about the dose efficiency of imaging modes involving the recording of intensity distributions in the near (Fresnel regime) or far (Fraunhofer regime) field downstream of a specimen. We present here a numerical study on the dose efficiency of near-field holography versus ptychography, a variant of far-field coherent diffraction imaging (CDI) involving multiple overlapping finite illumination positions. Unlike what has been reported for single-illumination CDI, we find that the quality, measured by spatial resolution and mean error, of reconstructed images from ptychography is similar (though slightly better) to what one can obtain from near-field holography at identical fluence on the specimen. These results support the concept that, if the experiment and image reconstruction are done properly, the sample can be near, or far; wherever you are, photon fluence on the specimen sets one limit to spatial resolution.