Abstract

© 2013 Author. Nonlinear all-X-ray signals that involve large core-atom separation compared to the X-ray wavelengths may not be described by the dipole approximation since they contain additional phase factors. Expressions for the rotationally averaged 2D X-ray photon echo signals from randomly oriented systems that take this positiondependent phase into account for arbitrary ratio between the core separation and the resonant wavelength are presented. Application is made to the Se K-edge of a selenium dipeptide system.