Coupled time and space focusing for time-of-flight inelastic scattering

We examine the time-focusing phenomena that occur in the operation of the crystal monochromator-Fermi-chopper time-of-flight spectrometer due to the correlation between transmitted wavelength and transmission time. Even with a flat monochromator the time-focusing has important consequences on the resolution width and on its dependence on the energy transfer. Time-focusing becomes critical for energy resolution with spatial focusing in the Bragg plane of the monochromator. We discuss the relation of the time-focusing conditions to the imaging conditions, object and image positions, and compare the analytically calculated resolution with simulation. Finally, the point of obtaining good wavevector transfer resolution through space focusing on the detector is presented. (orig.)