Absolute calibration of electric fields using Stark spectroscopy

We have established a direct link between laboratory electric fields and the atomic constants using Stark spectroscopy on n=15 sublevels of 7Li, coupled with an R-matrix theory of the Stark effect. Measurements are made with frequency-stabilized laser excitation by scanning the field from zero to above the saddle point. To estimate the zero-field energies we use quantum defect parameters from the polarization model for l4, and a fit to all available spectral data for l3. We claim that the electric field is known to about 2 ppm 5 mV/cm. Improvements and extensions are discussed.