Precise Measurement of the Hyperfine Splitting and Isotope Shift of the 8P1/2 State in 203Tl and 205Tl Using Two-Step Laser Spectroscopy

Description
The hyperfine splitting of the 8P1/2 excited state in 203Tl and 205Tl, as well as the isotope shift within the 7S1/2 --> 8P1/2 transition has been measured using two-step laser spectroscopy. Our measured values for the hyperfine splittings are 780.5(5) MHz in 203Tl and 788.3(7) in 205Tl, where the uncertainties in the last decimal place are combined statistical and systematic errors. The transition isotope shift of 203Tl relative to 205 Tl was measured to be 450.3(1.0) MHz. Our value for both hyperfine splittings is in reasonable agreement with the 1988 published values. However, our measurement of the 8P1/2 isotope shift relative to the ground state is 10 MHz less than the previous published value. In our experiment, one laser was locked to the 6P1/2 (F=1) --> 7S1/2 (F'=1) 378 nm transition, while a second, 672 nm red laser was scanned across the 7S1/2 (F'= 1) --> 8P1/2 (F''= 0,1) transitions. The two lasers were spatially overlapped inside a heated thallium vapour cell. Radiofrequency modulation of the laser was used to create sidebands in the absorption spectrum to introduce an method of frequency calibration internal to the absorption spectra.

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