Spectroscopy of Single Vacuum Arc Cathode Spots With Improved Sensitivity

Recently, we reported on the optical emission of vacuum arc discharges with a single cathode spot. The discharges were initiated by rectangular voltage pulses of 100-ns length produced by a cable generator. In combination with the application of a liquid Ga-In alloy cathode and ultrahigh vacuum conditions, a high reproducibility was obtained. An improvement of the sensitivity and the signal-to-noise ratio was achieved by the replacement of the streak camera by an intensified charge-coupled device camera. Thus, the accumulation of calibrated spectra with high temporal, spatial, and wavelength resolution was possible. Distinct differences in the temporal development of the atomic and ionic line intensities were found depending on the spatial position, that is, comparing the spot core and the spot surrounding.