Transition Radiation and Optical Bremsstrahlung from Electron-Irradiated Thin Films of Gold, Silver, and Copper

Abstract

The optical emission from electron-irradiated self-supported films (500-2000 Å thick ± 10%) of gold, silver, and copper has been investigated experimentally. Normally incident 1-μA beams of monoenergetic electrons having energies of 297, 423, 632 keV, and 1.10 MeV were used. The absolute photon intensity emitted in the 2200-5800-Å spectral region was measured with a calibrated optical system. The results were analyzed with respect to wavelength of emitted radiation, angular distribution in the forward direction (15°, 30°, and 45° from normal), and degree of polarization (parallel and perpendicular to the plane defined by the incident electrons and the emergent photons). The photon intensities measured in the perpendicular polarized direction clearly exhibit characteristics of bremsstrahlung. The transition-radiation contribution agrees very well with that predicted by the generalized theory of Ritchie and Eldridge when the bremsstrahlung is assumed to be unpolarized. From this, one may infer that interference between transition radiation and bremsstrahlung in the parallel plane does not grossly affect the emitted intensity. This investigation has extended the study of optical emission by Arakawa and co-workers to higher energies, thicker foils, and additional angles of emission.