Acquisition and processing of angle-resolved photoelectron spectra excited with focussed polarized resonance radiation

A system for the acquisition of angle-resolved photoelectron spectra is described. The sample gas is excited by VUV resonance radiation, which is polarized to about 95% using a fully rotatable fourfold reflection polarizer. One of the mirrors is toroidally shaped in order to focus the radiation into the sample gas cell. This design gives count rates comparable to those obtained by an unpolarized source, and at a greatly reduced background level. A computer controlled system has been developed to automate the recording procedure. It allows for simultaneous recordings of the spectra at the different angular settings, thus eliminating the effects of intensity drifts. Details of calibration procedures and data processing, including spectrum analysis, are given along with a discussion of the accuracy of the results. To illustrate the performance, measured β-values for the main components of the four outermost photoelectron bands in the Hel excited spectrum of CO₂ are presented.