Application of a Fabry-Perot spectrometer to the measurement of spectral line shifts much smaller than line width

It is shown that the presented method employing a Fabry-Perot spectrometer is significantly superior to existing methods using grating instruments of comparable size. The optimum choice of instrumental parameters is given. The method was employed to measure the flow velocity of an argon plasma jet via the Doppler effect of the 4158-A line. Results of these measurements are given.