Simultaneous long-time frequency stabilization of two dye lasers for a two-step atomic excitation

We describe a straightforward and accurate method for the frequency stabilization of two dye lasers on frequencies ν01 and ν02, fitting two atomic transitions from the ground state to the first electronically excited state and from there to a higher lying state. We make use of the Doppler shift by monitoring atomic fluorescence when the laser beams are crossed with an atomic beam under angles 90°-Δα and 90°+Δα, respectively. The laser frequency can be stabilized to better than ±1 MHz for the first and ±2 MHz for the second transition for periods of hours. We apply this stabilization method to collision experiments between two excited Nanl) atoms.