Transition Radiation and Optical Properties of Evaporated Carbon Foil*,†

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Abstract
The light emitted from an electron-irradiated self-supported foil (334±30 Å) of evaporated carbon has been investigated experimentally. Normally incident, 1-µA electron beams having monochromatic energies of 297, 423, 632 keV and 1.10 MeV were used. These correspond to β2 values of 0.6, 0.7, 0.8, and 0.9, respectively, where β=υ/c, and υ is the velocity of the incident electrons. 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, forward angle of emission, θ (15° and 30°), and degree of polarization (parallel and perpendicular to the plane of the incident electrons and observed light). The transition-radiation contribution determined from the parallel-polarized component has been compared with the generalized theory of Ritchie and Eldridge, using the optical constants of graphite and glassy carbon. From this comparison and a best-fit calculation, the optical constants for the carbon film throughout the 2200–5800-Å spectral region have been derived. The derived constants indicate that the carbon film has optical properties between those of graphite and glassy (amorphous) carbon. The results obtained stress the importance of measuring the optical constants of a given carbon film for any experiment in which they are needed.

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