Journal Article computer simulations Research Support, Non-U.S. Gov't compound refractive lens X-ray focusing synchrotron radiation Research Support, N.I.H., Extramural Research Support, U.S. Gov't, Non-P.H.S. Silicon Talbot effect X-ray absorption X-ray diffraction X-ray focusing theory X-ray nanofocusing X-ray transmission X-rays Z4152N8IUI analytical theory coherence compound refractive lenses computer simulation dentinal tubules diffraction diffraction focusing spectrometer effective aperture hard X-ray free-electron laser imaging iterative algorithm minimum X-ray beam size nanofocusing