The3S122−3D522interval in atomic hydrogen. III. Separated-oscillatory-field measurement

This paper reports the use of oscillatory fields in two spatially separated interaction regions to make a two-quantum radio-frequency measurement of the $3{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}-3\mathrm{}{}_{}{}^2{}_{}{}^{}D_{\frac{5}{2}}^{}{}_{}{}^{}$ fine-structure interval in atomic hydrogen. The measurement was carried out in zero magnetic field with a fast hydrogen beam. Radio-frequency fields from two separate oscillators were applied in both interaction regions and used to drive the two-quantum transition. The relative phase in the two interaction regions of one of the radio-frequency fields was alternated between 0° and 180° so as to isolate the separated-oscillatory-field interference signal; the frequency of the other radio-frequency field was varied so as to sweep over the resonance. An adaptation of the earlier reported theory was used to calculate the line shape and power dependence of the separated-oscillatory-field interference signal. The measured value for the $3{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}-3\mathrm{}{}_{}{}^2{}_{}{}^{}D_{\frac{5}{2}}^{}{}_{}{}^{}$ interval is 4013.106(57) MHz. This value agrees satisfactorily with both the previously reported single-radio-frequency-field measurement and the theoretical value for this interval. The value for the $3{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}-3\mathrm{}{}_{}{}^2{}_{}{}^{}D_{\frac{5}{2}}^{}{}_{}{}^{}$ interval obtained by combining the results from this measurement with the single-field measurements reported earlier is 4013.155(53) MHz.