Direct comparison of electric field measurement by fluorescence and optogalvanic Stark spectroscopies

Electric field in the cathode fall region of a 2.2 Torr helium de discharge with 0.8 mA cm(-2) current density has been measured from the Stark splitt ings of 11 P-1 (unperturbed) Rydberg transition by simultaneous optogalvani c (OG) and fluorescence techniques. The LIF Stark spectra showed narrower l inewidths compared to the OG spectra for higher parabolic quantum number st ates; LIF data also showed broader linewidths for higher parabolic quantum number states compared to the lines in the centre of the manifold. However, the electric fields obtained from the two methods were in agreement with e ach other within three per cent for all the measured locations in the sheat h. A comparison of the OG spectrum with the off-axis LIF data shows a combi nation of signal gain in the high-field region along with the Stark intensi ty distribution permits the line-of-sight-averaged OG spectrum to obtain ac curate field values in a discharge with modest radial field gradients.