Paper PS2-TuM10
Argon Microplasma Diagnostics by Diode Laser Absorption
Tuesday, November 10, 2009, 11:00 am, Room B2
Argon gas kinetic temperature and the resonance state (1s4) density in argon microplasma were measured by tunable diode laser absorption1. The experimental argon gas pressure was varied from 1 to 760 torr. A 900 MHz microstrip split ring resonator2,3 was used as the microplasma generator. A single-mode diode laser was tuned to scan through the argon 801.4nm line (1s4-2p7) by modulating the diode’s driving current. The output of the diode laser was collimated and passed through the microplasma. The obtained absorption lineshapes were fit by a Voigt profile, which is the convolution of Gaussian and Lorentz profiles. The Gaussian part corresponds to Doppler broadening and the Lorentz part corresponds to collisional and Stark broadening. Under our high-pressure experimental conditions, collisional broadening dominates and Stark broadening are almost negligible. Since the Doppler and collisional broadening can be expressed by a single variable T (gas temperature), the absorption lineshapes were fit with two parameters, amplitude and gas temperature4. The line integrated density of the resonance state was estimated from the integral of the absorption profile. The line integrated densities of argon 1s4 are 1.7x1015 m-3 m at 1 torr and 1.4x1015 m-3 m at 760 torr with 1W of input power. The visually observed length of plasma decreases from 1 cm at 1 torr to a few hundred microns at 760 Torr. The measured gas temperature increases from 350 K at 1 Torr to 750 K at 760 Torr. The microplasma is also simulated using a fluid model, which is compared with experimental measurements.1 D. Bear and R. Hanson, J. Quant. Spectrosc. Radiat. Transfer 47, 455 (1992).
2 F. Iza and J. Hopwood, Plasma Sources Sci. Technol. 14, 397 (2005).
3 F. Iza and J. Hopwood, IEEE Trans. on Plasma Sci. 31, 782 (2003).
4 S. Belostotskiy, V. Donnelly, D. Economou, and N. Sadeghi, IEEE Trans. on Plasma Sci., to appear June 2009.