Laser stabilisation for velocity-selective atomic absorption

A relatively simple method is described for stabilising a dye laser at a frequency ν = ν0 + νc in the vicinity of an atomic resonance frequency ν0. The Doppler effect is exploited by looking for atomic fluorescence when a laser beam is crossed with an atomic beam at certain angles αi. Absolute preselection of νc (the deviation from resonance) up to ~120 MHz is possible by the choice of αi, and a laser stabilisation to better than 1 MHz is obtained. We apply this stabilisation to collision experiments with velocity-selected excited Na atoms.