  Single-particle diagonal and off-diagonal Green's functions of a 2-leg t-J
ladder at 1/8-doping are investigated by Exact Diagonalisations techniques. A
numerically tractable expression for the superconducting gap is proposed and
the frequency dependence of the real and imaginary parts of the gap are
determined. The role of the low-energy gapped spin modes whose energies are
computed by a (one-step) Contractor Renormalization procedure are discussed.
