Thermal energy He3 spin-echo spectrometer for ultrahigh resolution surface dynamics measurements

Abstract

We present details of a He3 spin-echo spectrometer, designed to make possible a wide range of new surface dynamics measurements. The apparatus operates at beam energy of 8meV, sufficiently high to enable processes such as surface Bragg diffraction and permit inelastic and quasielastic scattering measurements at up to momentum transfers of about 4Å−1. We describe the requirements for the machine, details of the major components used to fulfil these requirements, and the performance of the overall spectrometer. The machine can access a Fourier time range of 0.01ps–1ns, and yields a resolution of 3μeV for inelastic spectrum reconstruction, although under favorable circumstances quasielastic broadenings as narrow as 20neV can be resolved, allowing correspondingly slower processes to be studied.