Temperature gradients, wavelength-dependent emissivity, and accuracy of high and very-high temperatures measured in the laser-heated diamond cell

Abstract

We have spectroradiometrically measured a suite of temperatures between 761 ± 128 and 7307 ± 958 K in the laser-heated diamond cell using Br₂ sample material. Critical evaluation of each spectrum and the dataset as a whole in comparison with synthetic data confirms the high temperatures and demonstrates the observable effects of temperature gradients and wavelength-dependent emissivity or absorbance on a single spectrum. In addition, we quantitatively demonstrate the use of a sliding two-color pyrometer analysis to produce a consistent and meaningful estimate of uncertainty of spectral temperature measurements.

Keywords:

• Laser heating
• High pressure
• High temperature
• Spectroradiometry
• Emissivity

Acknowledgements

Measurements made at the European Synchrotron Radiation Facility were performed as part of proposal HS-1877. The authors would like to thank Angès Dewaele, Gunnar Weck, Davina Sihachakr, Ramesh Andre, Wilson Crichton, Mohamed Mezouar, Nicolas Guignot, Abby Kavner, and Wendy Panero for experimental help and useful discussion.

Notes

¹We present several figures of real and synthetic data in Figures 3, 4, and 7. They are all identically arranged. Raw data (black) and the system response data (red, at 2500 K) are plotted together against wavelength (in nanometers). Just above the data, the Planck function (data/system response) is plotted (black) along with its fit (red) which is also against wavelength. At the top of the graph, the Wien function (black, see text), its fit (red), and the residual of the fit in percent (gray) are plotted against 1/wavelength (in meters) on the top axis. At the bottom of the plot, the results of the sliding two-color pyrometer at our best-chosen delta are shown. Two-color temperature (left axis) is plotted against wavelength. A histogram of that data (gray vertical bars representing 50 K bins) is plotted in the lower-left corner and fit to a Gaussian distribution (red).