Laser collimation of a chromium beam using Doppler force

We report on the collimation of a chromium atomic beam by one-dimensional transverse Doppler laser cooling. Operated on the cycling S-7(3) --> (7)p(4)(0) transition at 425.55 nm, the optical molasses laser power was 60 mW, which was detuned 2.5 MHz below the resonant frequency. The angular divergence of the atomic beam was reduced from 4.5 mrad to 0.48 mrad, corresponding to a transverse velocity of +/-0.46 m/s, and the relevant transverse temperature is 265 mu K.