Light Scattering from Rotons in Liquid Helium

Abstract

We have measured the spectrum, intensity, and polarization of light Raman scattered from rotons and higher energy quasiparticle excitations in liquid ${\mathrm{He}}^{4}$ for temperatures between 1.16 and 2.14\ifmmode^\circ\else\textdegree\fi{}K. The effect on the spectrum of the temperature-dependent energy and lifetime of the rotons is clearly visible. At a scattering angle of 90\ifmmode^\circ\else\textdegree\fi{} the light is highly depolarized and about three orders of magnitude weaker than the Brillouin scatering from the phonons.