The present article gives a review of various photoassociation (PA) experiments performed at ENS with a gas of ultracold atoms of metastable helium in the 23S1 state, using a PA laser beam red-detuned from the 23S1-23P transitions. Molecular spectra close to the D2 atomic line (23S \documentclass[12pt]{minimal}
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\begin{document}$_1\leftrightarrow 2^3$\end{document}P2) are presented. All the measured lines are identified as a signature of molecular bound states having a strong (if not pure) quintet spin character at short interatomic distance. Close to the D0 atomic line (23S \documentclass[12pt]{minimal}
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\begin{document}$_1\leftrightarrow 2^3$\end{document}P0), giant helium dimers can be produced [see Phys. Rev. Lett. 91, 073203 (2003)]. A laser set-up improved recently allows us to measure very accurately the binding energy of the ro-vibrational ground state of the 0u + purely long-range potential and the agreement with the theory published previously is excellent. Finally, preliminary results on 2 photon PA spectroscopy are given.
