Tunable frequency-stabilization of an ultraviolet laser using a hollow-cathode lamp of atomic thallium

A frequency-stabilized ultraviolet laser system, locked to the thallium resonant transition at 377.5 nm, was demonstrated using a novel bichromatic spectroscopy technique for tuning the zero-crossing laser-lock point. The 377.5 nm 6P1/2→7S1/2 transition is important for thallium laser cooling and trapping experiments. The pressure shift, owing to the high pressure buffer gas of the hollow-cathode lamp, was observed using an atomic beam resonance as the reference. Such a shift was corrected by adjusting the peak ratio of the two Doppler-free saturation profiles that resulted from the two pumping beams with a 130 MHz frequency difference. The resulting frequency stability of the ultraviolet laser was 0.5 MHz at a 0.1 s integration time. This scheme is compact and versatile for stabilizing laser systems, which require a sub-megahertz stability and frequency tunability.