Resonant Doppler velocimetry of He flow discharge

We demonstrated the resonant Doppler velocimetry of He atoms in a flowing DC plasma. The laser-induced emission of He atoms was detected while the wavelength of a dye laser was scanned (LIF excitation spectroscopy), and the flow velocity was derived from the Doppler shift of the observed spectral line. The overall accuracy of measured velocity was 30-60 ms-1. We found that flow velocity exhibited a significant dependence on the discharge current at a constant flow rate. We also observed a spectrum by the LIF excitation method combined with Lamb's dip technique. The combination method was useful when the spectral line exhibited Stark shift.