Double-slit X-ray dynamical diffraction in elastically deformed crystals

Double-slit X-ray Laue symmetrical case dynamical diffraction in a crystal influenced by a constant temperature gradient perpendicular to the reflecting atomic planes is investigated. It is shown that on the exit surface of the crystal interference fringes similar to Young's fringes, known in optics, are formed. The contrast depends on the direction of the applied temperature gradient: it is better when the direction of the temperature gradient is parallel to the diffraction vector. For the period of the fringes an expression is obtained, which depends on the modulus of the temperature gradient and is polarization sensitive. The position of the fringes in the cross section of the beam depends on the deviation of the beam from the generalized exact Bragg angle in the deformed crystal. The deviation of the incident beam from the generalized exact Bragg direction on the order of one hundredth of an arc-second may cause a shift of the interference fringes from the centre of the beam on the order of 10 µm.