Composition Variation of Optical Phonon Damping in Lithium Niobate Crystals

By solving analytically and numerically dynamical diffraction equations, we study the modulation of X-rays in ideal crystals by a co-propagating wave of impulsively excited optical phonons. Our results for a diamond crystal suggest that the output diffracted X-ray field can have a time structure much shorter than the period of the excited vibrational mode (Tv= 25fs). We explain this dynamics in terms of high-order Raman scattering of X-rays by optical phonons. The potential of this ultrafast modulation technique for controlling X-rays from synchrotron and FEL sources is discussed.