Measurement of the He 2³S state atom density in an inductively coupled

Helium 2³S metastable atoms play key roles in discharge plasmas because of the long lifetime and large excitation energy. In this research, 2³S state helium density in an inductively coupled plasma (ICP) was measured by laser absorption spectroscopy. He plasma was operated at the He pressure of 20~50 mTorr and by a RF power supply with the maximum power of 1.5 kW. Electron temperature and electron density of plasma were 2~3 eV and ~10¹² cm^-3, respectively. Absorption spectra for the 2³S₁->2³P_i (i=0, 1, 2) transitions were measured by an external cavity laser diode (ECLD) at 1083 nm. The 2³S state helium density was analysed and discussed with the RF power and the radial position in the plasma chamber.