ELECTRIC-FIELD DEPENDENCE OF E1 TRANSITIONS BETWEEN HIGHLY EXCITED HYDROGEN STARK SUBLEVELS

We have measured certain ratios of transition intensities between excited hydrogen Stark sublevels over a range of electric-field values. CO2 lasers were used to excite a fast beam of hydrogen atoms. The pi-polarized transitions studied were from extremal Stark sublevels of principal quantum number n=10 to extremal and next extremal sublevels of n=30 and 44, at fields from 2 to 700 V/cm. The observed ratios are compared with those obtained using a non-relativistic zero-field formula attributed to Gordon [Ann. Phys. (Leipzig) 2, 1031 (1929)] and with calculations employing matrix diagonalization including fine structure. Even for these relatively high n values, we find at low field significant deviations from results from Gordon's formula due to fine structure in the lower state as well as deviations at high field due to n mixing in the upper state induced by the static electric field. The experimental results and the matrix diagonalization calculations agree to within a few percent, which is the order of magnitude of possible saturation effects.