Estimation of sheath electric field in inductively coupled hydrogen plasma on the basis of Doppler-broadened absorption spectrum of hydrogen Balmer-α line

Abstract

We examined the applicability of the Doppler-broadened absorption spectrum of the hydrogen Balmer-α line to the estimation of the sheath electric field in plasma. The Stark splitting of the fine-structure components was calculated by solving the time-independent Schrödinger equation at various electric field strengths, and the theoretical absorption spectrum was obtained by the superposition of the fine-structure components with the same Doppler broadening widths. The spectrum of the Balmer-α line of atomic hydrogen, which was measured by standard diode laser absorption spectroscopy, was fitted with the theoretical spectrum. We succeeded in determining the translational temperature of atomic hydrogen, which was obtained from the Doppler broadening width, and the electric field strength by the spectral fitting. We have evaluated that the minimum electric field strength that can be detected by the present method is approximately 350 V cm−1 when the translational temperature of atomic hydrogen is 400–500 K.