Argon Microplasma Diagnostics by Diode Laser Absorption

The densities of argon excited states (1s3, 1s4, and 1s5) and the gas temperature of argon microplasma were measured by diode laser absorption. A 900-MHz microstrip split-ring resonator was used to excite the argon microplasma with gas pressures between 1 and 760 torr. The line-integrated excited-state densities and gas temperature of these states were estimated by the integrated absorption and broadening of the measured lineshapes, respectively. The excited-state densities were found to be minimum around 50 torr and increased with either decreasing or increasing pressure. The gas temperature increases from 300 K to 900 K as pressure increases from 1 to 760 torr.