Light Scattering from Solid Helium

Abstract

Brillouin and Raman scattering efficiencies from the solid phases of helium are calculated, assuming a model which regards each helium atom as a neutral but polarizable point mass. In the hcp phase, only the lowest-frequency optical modes are Raman active and they are estimated to have a scattering efficiency roughly two orders of magnitude less than the Brillouin efficiency. Two-phonon scattering is also considered and is estimated to be three orders of magnitude weaker than the Brillouin scattering. This latter estimate is also expected to apply to the superfluid liquid phase and confirms an independent calculation by Stephen. Such an estimate agrees with the recent observations by Greytak and Yan, following a suggestion by Halley.