Speaker
Prof.
Masahiro Hasuo
(Kyoto University)
Description
Atmospheric-pressure plasmas have been attracting much interest because of their possibility for various applications, such as surface treatment, nano-particle formation and pollution gas processing [1]. One of the methods to generate high-pressure plasmas at moderate voltage is a microhollow cathode discharge. The gas temperature and electron density of microhollow cathode plasmas have been measured with emission spectroscopy [2].
In comparison with the emission spectroscopy, laser absorption spectroscopy is nearly free from spectral resolution. Since the spectral line width at atmospheric pressure broadens over several tens of GHz in full width at half maximum mainly due to the pressure broadening, we used a vertical-cavity surface-emitting Laser diode, which can scan the light frequency over several hundreds of GHz. We measured the absorption spectra of the helium 1s2p(^1P) -1s3d(^1D) transition with the spatial resolution of 0.030 mm in the Rayleigh criterion for the 0.3 mm diameter microhollow cathode helium plasmas [3]. The gas pressure ranged from 10 to 100 kPa.
For the pressure below 20 kPa, the observed spectra near the electrode were asymmetric. By fitting the observed spectra with Voigt functions including the DC Stark effect, we evaluated the electric field strength, 1s2p(^1P) atom density, gas temperature and electron density, and then made two-dimensional maps of these quantities [3]. Since clear asymmetry was not detected in the observed spectra for the pressure over 20 kPa, we made two-dimensional maps of the 1s2p(^1P) atom density, gas temperature and electron density. We also performed such absorption spectroscopy of the argon 1s_5 – 2p_6 transition (Paschen notation) at for microhollow cathode argon plasmas.
This work was partly supported by JSPS KAKENHI Grant-in-Aid for Challenging Exploratory Research (No.15K13607).
[1] D. Mariotti, R. M. Sankaran, J. Phys. D: Appl. Phys. 44, (2011) 174023.
[2] S. Namba, T. Yamasaki, Y. Hane, D. Fukuhara, K. Kozue, K. Takiyama, J. Appl. Phys. 110, (2011) 073307.
[3] K. Torii, S. Yamawaki, K. Katayama, S. Namba, K. Fujii, T. Shikama, M. Hasuo, Plasma and Fusion Res. 10, (2015) 3406063.
Primary author
Prof.
Masahiro Hasuo
(Kyoto University)
