Prospects for measurement and control of the scattering length of   metastable helium using photoassociation techniques
  A numerical investigation of two-laser photoassociation (PA) spectroscopy on spin-polarized metastable helium (He*) atoms is presented within the context of experimental observation of the least-bound energy level in the scattering potential and subsequent determination of the s-wave scattering length. Starting out from the model developed by Bohn and Julienne [Phys. Rev. A \textbf{60}, (1999) 414], PA rate coefficients are obtained as a function of the parameters of the two lasers. The rate coefficients are used to simulate one- and two-laser PA spectra. The results demonstrate the feasibility of a spectroscopic determination of the binding energy of the least-bound level. The simulated spectra may be used as a guideline when designing such an experiment, whereas the model may also be employed for fitting experimentally obtained PA spectra. In addition, the prospects for substantial modification of the He* scattering length by means of optical Feshbach resonances are considered. Several experimental issues relating to the numerical investigation presented here are discussed. 
J.C.J. Koelemeij and M. Leduc