Precision mapping of dc electric fields using interference-narrowed Stark resonances

The authors have developed a technique for mapping electrostatic fields with unprecedented spatial resolution and have used it for fields of a few kV/cm. The method exploits interference narrowing of linewidths or lifetime enhancement of Stark states. In the experiments, Rb atoms in a thermal beam are stepwise excited by two crossed laser beams from the 5² S state via the 5² P state to Stark states near the saddle point. Choosing a spectral feature whose lifetime changes rapidly but not precipitously with the field near interference, the authors measure its decay rate at various positions by moving the intersection region of the laser beams that stepwise excite the resonance of interest. From knowledge of the field dependence of the lifetime of a particular state and the measured lifetime at various positions, a map of the electric field is produced. Field changes as small as ±25 ppm can be detected. The method has been used to map the fields between two plates in the vicinity of various slits and grid-covered apertures.