Systematic errors in electron-photon coincidence measurements of the 3(1)p state of helium

The coherence parameters associated with the electron impact excitation of the He 3(1)P state are studied for a Monte Carlo simulation of an experiment consisting of crossed electron and atom beams. The effects of changes in gas pressure and interaction region geometry are monitored by a fixed polarimeter analyzing radiation resulting from the 3(1)p to 1(1)S (53.7 nm) transition. This work extends the simulations of Humphrey (1999) with the incorporation of a finite electron detector, a region of background gas, and angular dispersion in the electron beam. Humphrey found that with an infinitesimal electron detector, the measured polarizations were not strongly dependent on interaction region geometry. In this work, however, it is found that the coherence parameters are very strongly dependent on interaction region geometry, pressure, and the solid angle of the electron detector. Even very small solid angles can adversely affect the measured parameters. T (Author)