Resonance time Modulation of X-ray Diffraction in Crystals Deformed by Ultrasound

A theory of frequency modulation of X-rays by ultrasound during dynamical diffraction in crystals is presented. The modulation of X-rays has been analysed as a function of the frequency of the ultrasonic wave. The existence of a new physical phenomenon, a resonance time modulation of X-ray beams in the radio-frequency range, has been predicted. It is shown that, at certain frequencies, the modulation strength is increased several times for the same amplitude of ultrasonic wave. The conditions required for the optimum frequency modulation are different from that for the X-ray acoustic resonance [Entin (1977). Zh. Eksp. Teor. Fiz. Pisma Red. 26, 392-395]. For a weak ultrasonic deformation, the resonant frequency of time modulation is approximately 2^1/2 times higher than the frequency for X-ray-acoustic resonance.