Application of Millimeter-Wave Heterodyne Spectroscopy With a Superconducting Receiver for Dusty Plasma Diagnostics

Diagnosing the physical and chemical states of minor constituents in dusty plasma, including their temperature and abundance, is challenging. In this research, the spectral lines of HCN formed in capacitively coupled plasma (CCP) were measured by 0.17–0.19-THz band heterodyne spectroscopy using a superconductor/insulator/superconductor receiver and a new modified chopper-wheel calibration technique. The rotational temperature of N $_{2}$ determined by optical emission spectroscopy is approximately 310–380 K, which is similar to the kinetic temperature of the plasma gas, while the rotational temperature of HCN is estimated to be approximately 400–570 K. This suggests that the HCN in the observation field of view contains components affected by high-energy physical processes such as sputtering and photochemistry during the formation process. This passive heterodyne spectroscopic technique in the millimeter to THz frequency band will provide a useful tool for diagnosing the physical and chemical conditions of dusty plasma.