Optical emission spectroscopy of low-pressure DC argon plasmas for reconfigurable metadevices

Plasma discharge tubes (PDTs) are a promising medium for dynamically reconfigurable metasurfaces, owing to their tunable electron density ( ne). This work provides an empirical framework for designing low-pressure, direct current-driven argon PDTs by defining their operational limits. Optical emission spectroscopy was utilized to characterize the spatial distributions of excitation temperature ( Texc) and electron density ne, via Boltzmann plots and Stark broadening, respectively. Under stable operation, it was observed that increased gas pressure of PDTs resulted in a decrease in Texc and a corresponding increase in ne. However, a critical failure mode was identified at high currents. This degradation, characterized by a white glow, quenched argon emission, and electrical instability, was attributed to ion-induced sputtering of the nickel hollow cathode of PDTs. These findings indicate that the operational current must be maintained within a well-defined range to ensure device viability and lifetime, thus offering a critical design guideline for the development of robust plasma-based reconfigurable metasurfaces.