Optical constants of relaxed, derelaxed, and partially relaxed amorphous silicon (a‐Si) in the range 0.4–0.9 &mgr;m are reported. The thermodynamical state of amorphous silicon (a‐Si) has been changed either by thermal treatments or low dose ion implantation. Ellipsometry has been used to evaluate the complex refractive index for several amorphous states with enthalpy content between that of the fully relaxed and fully derelaxeda‐Si. We observed a strong correlation between the electronic structure as probed by our optical measurements and the topological short‐range order as probed by Raman scattering.