High-resolution imaging of vacuum arc cathode spots

Imaging differential laser absorption spectroscopy was used to map the electron density distribution of vacuum arc cathode spots. The temporal resolution was determined by the sequence of laser pulses (pulses of 0.4-ns duration, with 3-ns separation). The spatial resolution was limited by diffraction (better than 5 /spl mu/m). Fragments of cathode spots have been detected, and the following parameters could be derived: current density on the order of 10/sup 12/ A/m/sup 2/, plasma density greater than 3-6/spl times/10/sup 26/ m/sup -3/, fragment size 5-10 /spl mu/m and smaller, current per fragment 20-40 A (for copper electrodes and are current 50-150 A), and the lifetime of dense plasma on the order of a few nanoseconds.