Opacity of Dense, Cold, and Strongly Coupled Plasmas.

The physics of dense $[(1\ensuremath{-}5)\ifmmode\times\else\texttimes\fi{}{10}^{19}{\mathrm{cm}}^{\ensuremath{-}3}]$, cold (1--15 eV), strongly coupled $(\ensuremath{\gamma}\ensuremath{\sim}0.7)$ plasmas is probed with 0.351, 0.527, and 1.054 $\ensuremath{\mu}\mathrm{m}$ opacity measurements in well characterized, laser-heated, aluminum plasmas. Current opacity models are tested, for the first time, in the regime where the probing photon energies are of the same order as the average interparticle interaction energies in the plasma. Predicted enhancements of the opacity at low temperatures are not observed, but overall agreement between experiment and theory is within a factor of 2.