Dependence of phantom current in a metal vapor laser on electrode geometry

It is observed that the discharge current in a copper vapor laser rises prior to the voltage breakdown. This current, which appears almost 50 ns before the discharge breakdown and is equivalent to almost 70% of the peak current at the time of breakdown, is termed the phantom current. It is reported that by reducing the residual electron density (phantom current) in a metal vapor laser (MVL), its performance can be significantly improved. Metallic pins are used in the electrode to facilitate discharge in the long discharge tube. Besides augmenting the discharge during the initial stage, it has a significant impact on the laser performance. In this paper, we find out the correlation between the phantom current and the electrode pin geometry and then present the optimum electrode geometry for improved laser performance. It was observed that the number of pins in the electrode affects the localized electric field in the nearby region and plays a dominant role in the quantum of the phantom current in the discharge tube of the laser. The MVL system was tested with electrodes that had a different number of pins (zero, eight and 36) and it was found that the phantom current is minimum when the electrode has zero pins and highest with an eight-pin electrode.