A new measurement of s-wave scattering length of metastable helium atoms by photoassociative spectroscopy

The paper reports on a new measurement method of the s-wave scattering length of metastable helium atoms by photoassociation (PA) technique. Lightshifts of the PA resonance lines are measured, which results from the coupling of a bound state in the excited state potential and the continuum of scattering states above the ground state potential. Ultracold molecules are formed by photoassociation from spin-polarized metastable helium atoms, which are trapped in a magnetic trap and cooled down to a temperature of 16 μK by evaporative cooling technique. The PA laser is red detuned to the atomic D0 line (2³S-2³P₀) and scanned around the bound state levels in the purely long-range 0₀⁺ potential to provide precise PA spectra.