Improving the Hugoniot Temperatures of Iron Through Measured and Modeled Thermo-Optical Properties

For opaque samples in shock compression experiments bounded by a window, the interface between the sample and window can complicate optical methods of temperature determination. Additional considerations such as thermal conduction across the sample-window interface and materials properties differences between the Hugoniot and interface pressures of the sample need to be factored into the derived temperature. This compounds upon uncertainties already present in optical pyrometry methods, such as in sample emissivity and calibration reliability. To expand upon the temperature convergence behavior of iron across a Fe-LiF interface and to further reduce associated uncertainties, we have performed a series of gas gun compression experiments on iron up to 240 GPa utilizing discrete-wavelength pyrometry, streaked optical pyrometry, in situ reflectivity collection, and modeled emissivity behavior of the iron at equivalent temperatures and pressures. Our results show that incorporating wavelength, temperature, and time-resolved reflectivity information improves temperature fits and reduce derived Hugoniot temperature uncertainty.