Measuring surface phonons with a 3He spin echo spectrometer: a two-dimensional approach.

The helium spin echo spectrometer is a powerful apparatus for measuring surface dynamics and can be used in several different modes of operation. In this paper we present the first two-dimensional measurements of the wavelength intensity matrix, offering a new approach for studying surface phonons. The approach that we present is completely independent of the incident beam energy distribution and hence can be used to study inelastic scattering with ultra-high resolution. The additional insights obtained by using this new approach and its technical difficulties are discussed, and a comparison with other existing methods is given.