Photo-Mechanical Effect of Photoassociation : a New Method to Measure the Scattering Length of Ultracold Metastable Helium Atoms

We report on a new method to detect photoassociation resonance signals with the collective dipole oscillations induced by the excitation laser momentum in a cold atomic cloud confined in a magnetic trap. A precise value for the s-wave scattering length, a=7.48(+0.29/-0.36) nm is found, which agrees well with our previous measurements.