Three-dimensional distribution measurement of electric fields using Stark effect in NaK

Three-dimensional distribution measurement of electric fields has been demonstrated by applying the Stark effect of sodium-potassium (NaK) molecules. The magnitude of the electric field is determined from the intensity ratio of the Q-branch line to that of the P- and R-branch lines in the laser-induced fluorescence (LIF) spectrum because the Stark level mixing effect gives rise to the appearance of the ''forbidden'' Q line. A method for determining the field polarity is also proposed, in which the intensity variation of the LIF is phase-sensitively detected by superimposing a reference ac field on the de field to be measured.