We extend the study of Kapitza-Dirac diffraction in Raman-Nath regime removing the limitations put on
resonance detuning. Discussing the case of extended Raman-Nath regime we develop an approximation for the case
of strong standing waves which will correspond to the well known tight-binding approximation for periodic
structures. Due to internal structure of the diffracting particles the system eigenvalues and eigenfunctions show
important differences from the generally known cases.