Measurement of isotope shifts and hyperfine splittings of ytterbium by means of acousto-optic modulation

The isotope and hyperfine shifts for the Yb 1S0(6s2)→3P1(6s6p) transition were determined with an acousto-optic modulator used to frequency shift part of a laser beam. The frequency-shifted and -unshifted laser beams were superimposed and excited an atomic beam. The laser was scanned across the transition while fluorescence produced by the radiative decay of the excited state was detected by a photomultiplier. Each isotope generated two peaks in the spectrum separated by the acousto-optic shift, which permitted the frequency to be calibrated. This relatively simple method yields results that agree well with the most accurate existing data, which were obtained by measurement of frequency shifts with a Fabry--Perot etalon whose length was stabilized with a helium--neon laser locked to an iodine line