On the Influence of Parallax Effects in Thick Silicon Sensors in Coherent Diffraction Imaging

Abstract Structure determination of, e.g., single molecules is a key application of X-ray free-electron lasers (XFELs) and 4 th generation synchrotron sources, particularly using the coherent and pulsed X-ray radiation from XFELs. Scientific interest focuses on understanding the physical, biological, and chemical properties of samples at the nanometer scale. The X-rays from XFELs enable Coherent X-ray Diffraction Imaging (CXDI), where coherent X-rays irradiate a sample, and a far-field diffraction pattern is captured by an imaging detector. By the nature of the underlying physics, the resolution, at which the molecular structure of a sample can be probed with the CXDI technique, is limited by the wavelength of the X-ray radiation and the exposure time if a detector can record the diffraction pattern up to very large scattering angles. The resolution that can be achieved under real experimental conditions, depends strongly on additional parameters. The Shannon pixel size, linked to the detector resolution, the coherent dose that can be deposited in the sample without changing its structure, the image contrast, and the signal-to-noise ratio of the detected scattered radiation at high q , i.e., at high scattering angles 2Θ, have a strong influence on the resolution. The signal-to-noise ratio at high q defines the “effective” maximum solid angle in a specific experiment setup at which a detector can efficiently detect a signal and in consequence determines the achievable resolution. The image contrast defines how well bright image features can be distinguished from dark ones. We present the preliminary results of our study on the influence of the point spread function on the signal-to-noise ratio, image contrast, position resolution, and achievable sample resolution for different pixel sizes.