Electric field measurements in discharges by Doppler-free two-photon laser Stark spectroscopy of atomic hydrogen

We show experimentally that the Doppler-free, two-photon excitation of n = 3 states of atomic hydrogen using a tunable, narrow band laser source at 205 nm, can be used to measure the electric field in the sheath of a low pressure glow discharge with good sensitivity (50 V/cm). The observed excitation spectra show a well-resolved Stark structure in good agreement with simulated spectra calculated for different values of the electric field. This method is promising for measuring the electric field magnitude in a number of environments because of the large laser induced fluorescence yield per ground state H atom.