High-resolution spectroscopy and frequency measurement of the midinfrared 5d/sup 2/D/sub 3/2/-5d/sup 2/D/sub 5/2/ transition of a single laser-cooled barium ion

The narrow 12.5- mu m, 5d/sup 2/D/sub 3/2/-5d/sup 2/D/sub 5/2/ fine-structure transition in a laser-cooled, single Ba/sup +/ atom was probed with a tunable sideband from a frequency-stable /sup 15/NH/sub 3/ laser operating on the sP(8, 6) transition. Single-ion Doppler-free resonances with negligible time dilation shift are observed without any detected motional sidebands for each Zeeman component. Linewidths of 11 kHz are observed for the components, which are currently limited by the probe laser frequency excursions. A measurement of the D-D transition center frequency relative to the sP(8, 6) saturated absorption is performed. A preliminary measurement of the sP(8, 6) line center frequency gives the line center for the /sup 138/Ba/sup +/ isotope transition as 24012.048.5+or-0.2 MHz.<
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