A laser heating system that stabilizes and controls the temperature: Diamond anvil cell applications

A laser heating system is described for use with diamond anvil high pressure cells that directly senses and stabilizes visible thermal radiation emitted by hot samples. This technique stabilizes sample temperatures better than other methods and allows superior temperature control. Calibration of the system was checked by measuring the melting temperatures of five metals at ambient pressure. Assuming literature values for spectral emissivity, the calibration was found to be accurate to 3.3% (based upon one standard deviation of the percentage error from published melting temperatures). Performance of the laser heating system was verified by heating iron foil at 13 GPa. With the sample intensity unstabilized, mean temperature was 3003 K with a standard deviation of 144 K, while with it stabilized, mean temperature was 3051 K with a standard deviation of 8 K. For a given wavelength-dependent emissivity, the difference between the actual temperature and the greybody temperature increases as the temperature increases. Therefore, to accurately determine temperatures at the high temperatures applicable to solid Earth geophysics (1500–6000 K), wavelength-dependent emissivity cannot be ignored.