Precise laser frequency scanning using frequency-synthesized optical frequency sidebands: application to isotope shifts and hyperfine structure of mercury

Based on an efficient (30%), broadband (~3.5-GHz) electro-optic modulator producing rf optical sidebands locked to a stable cavity, we can scan a tunable dye laser under computer control with frequency-synthesizer precision. Cavity drift is suppressed in software by using a strong feature in the spectrum for stabilization. Mercury isotope shifts (546 nm 63P2 → 73S1) have been measured with a reproducibility of ~50 kHz. This accuracy of ~1/300 of the linewidth illustrates the power of the technique. Derived hyperfine-structure constants are compared with previous atomic-beam data where available.