TEMPERATURE-DEPENDENCE OF THE 2-ROTON RAMAN-SPECTRUM OF SUPERFLUID HE-4

Temperature dependence of the two-roton Raman spectrum of superfluid H e-4 was measured at pressures of saturated vapor pressure, 9.8 x 10(4) Pa, 4.9 x 10(5) Pa, and 1.96 x 10(6) Pa from the lowest temperature o f 0.75 K to temperatures above the lambda point. The temperature depen dence of both the spectral shape and intensity of the two-roton peak h as been found to be simulated well by a model, where the temperature e ffect is simply broadening of the spectrum with small variation of the roton minimum energy. Spectral shape and peak height at elevated temp eratures have been found to be reproduced by convolution integrals of the spectrum at the lowest temperature with Lorentzian functions which take into account the temperature broadening effect at each temperatu re, where also small temperature dependence of the roton minimum energ y had to be taken into account in order to fit the spectrum position. The fact verifies that the Raman spectral shape of superfluid 4He does not change qualitatively at elevated temperatures and also even cross ing the lambda point. By the model analysis, temperature dependence of the roton minimum energy and the roton half width (inverse of the rot on lifetime) have been determined at each pressure as a function of te mperature. The results have been compared with theories.