REFLECTIVITY OF SOUND-EXCITED CRYSTALS MEASURED ON A DOUBLE-CRYSTAL DIFFRACTOMETER

A longitudinal ultrasound standing wave modulates the regular arrangem ent of atomic planes in a crystal in two ways: first, the spacing of t he lattice planes is modified, introducing a macroscopic strain and se cond, the lattice planes oscillate with considerable velocity. Bragg r eflection from the strain maintains the energy of the radiation, while reflection from the moving planes gives rise to a Doppler shift. From a measurement of the rocking width of a vibrating crystal the atomic vibration amplitude can be determined. (C) 1998 Elsevier Science B.V. All rights reserved.