Aluminium K_a emission (1.5 keV) produced by an 8 J, 500 ps, Nd:glass laser incident at 45° onto a layered target of 0.8  µm thick aluminium (front side) and 1 μm thick iron (backside) has been used to probe the opacity of iron plasma. Source broadened spectroscopy and continuum emission analysis show that whole beam self-focusing within the aluminium plasma results in a two-temperature spatial distribution. Thermal conduction from the laser-irradiated aluminium into the iron layer, enhanced by the whole beam self-focusing, results in a temperature of ~10.150 eV in the iron layer. The iron opacity at a photon energy of 1.5 keV is shown to be strongly modified from cold values in agreement with IMP code opacities. Results presented here represent a feasibility study to seed future work using table-top laser systems for plasma opacity experiments.