“Reflectance Thermometry for Time-Resolved Measurements of Low-Temperature Compression on Sandia’s Z Machine"*

Pulsed current from Sandia’s Z machine compresses samples to 10-1000 GPa pressures on nanosecond time scales. Such rapid compression results in 10-100,000 K temperature (T) changes, depending on how loading is applied. Shock compression of solids leads to T above 2000 K, whereas ramp compression to the same pressure leads to T below 1000 K. Optical pyrometry is well-suited for the former but impractical for the latter—samples do not emit enough photons for such high-speed measurements. To fill this gap, we are investigating the thermo-reflectance of aluminum as an optical thermometer. Aluminum has an absorption feature at 1.5 eV that shifts to higher energy under static compression and in the opposite direction upon heating. We carried out static compression of Al in diamond anvil cell at high T, coupled with reflectivity measurements. The distinction between absorption energies at higher T for any given pressure is promising for the calibration of an optical thermometer for Z.