Does laser-driven heat front propagation depend on material microstructure?

We showed earlier that the laser-driven heat front propagation velocity in low-density Ti-silica aerogel and TiO$_{\mathrm{2}}$ foam targets was slower than that simulated with a 2D radiation-hydrodynamics code incorporating an atomic kinetics model in non-LTE and assuming initially homogeneous material (F. P\'{e}rez, et al., Physics of Plasmas 21, 023102, 2014). Some theoretical models suggest that the heat front is slowed over what it would be in a homogeneous medium by the microstructure of the foam. In order to test this hypothesis we designed and conducted a comparison experiment on the GEKKO laser to measure heat front propagation velocity in two targets, one an Ar/CO$_{\mathrm{2}}$ gas mixture and the other a TiO$_{\mathrm{2}}$ foam, that had identical initial densities and average ionization states. We found that the heat front traveled about ten times faster in the gas than in the foam. We present the details of the experiment design and a comparison of the data with the simulations.