Superconducting Tunnel Junctions (STJ) are promising devices as a next gene
ration of nuclear and optical detectors Non-equilibrium experiments can pro
,ide useful information on the behaviour of a perturbed superconductor. Amo
ng possible non-equilibrium sources, we used quasi-particle injection in th
ree-terminal double tunnel junction de,ices and a laser pumping source. We
investigated the effect of perturbed renditions on sub-harmonic gap structu
res, which are present in I-V characteristics of high quality Nb-based STJs
. Experimental results concerning the change of the energy gap measured at
V=2 Delta/2e show features which can not be completely explained in terms o
f simple heating effects.