Journal Article third-order nonlinearity X-ray dynamical diffraction Bragg case X-ray Fraunhofer holography X-ray microscopy nonlinear diffraction reflection region two-wave diffraction Bragg reflection Published Erratum Talbot effect X-ray X-ray lens X-ray point focusing X-ray pulse crystal crystals dynamical diffraction eikonal approximation exact solution. image processing image reconstruction nonlinear dynamical diffraction periodic object time-dependent propagation equations