Electron impact excitation of the 3 1D state of helium an electron-photon coherence study at small scattering angles

Electron impact excitation of the 3 (1)D state of helium has been studied using the scattered electron-polarized photon correlation method. Results are presented at incident electron energies of 26.5, 29.6, 40.0, 45.0 and 60.0 eV for scattering angles up to 40 degrees. The data presented here complement the previous large angle data from this laboratory and taken together provide a complete mapping of the dimensionless parameters characterizing excitation of the 3 (1)D state of helium over a wide range of both angle and energy. Strong variations in the parameters as a function of energy and angle are discussed. Good agreement is observed between the experimental data and recent theoretical predictions.