Copper halides (especially CuCl) have played an important role in the
development of nonlinear optical spectroscopy. The binding energies of
excitons and of biexcitons are so large that the optical response of
these materials and its dynamics could be fully described in the frame
of these quasi-particle states and of their mutual interactions. We s
hall go through the different steps of the development of this researc
h and present the contribution of the Strasbourg Group to this activit
y.