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

Abstract

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.

Carbon precipitation from heavy hydrocarbon fluid in deep planetary interiors

“…Temperature uncertainties related to the solution of Planck's equation are relatively small (o1% relative), which is consistent with the results of thorough reports on accuracy of temperature measurements in LH DACs [39][40][41] . Errors introduced by the optical system were compensated by calibrating the response to tungsten lamp light source.…”

“…The major source of errors in temperature measurements is introduced by approximations for sample emissivity. Namely, the greybody approximation used in this work is known to be a potential source of substantial errors that are on the order of ±100-150 K (refs 39,40), as sample emissivity is wavelength-dependent and was not characterized as a function of pressure and temperature.…”

Laser beam shaping for studying thermally induced damage

“…Previously, such studies were conducted in hot-filaments 28 , diamond anvil cells (DAC) 29 and microwave plasma 30 . In this work, the same effect was created with the added advantage of localised heating down to the diffraction limit of the laser beam spot size, thus opening the way to controlled spatial studies on diamond heated samples.…”

MELTING TEMPERATURE DETERMINATION BY TRACK FORMATION TECHNIQUE USING CO2LASER

“…Also, a fast IR camera is employed to obtain information about the uniformity of T distribution across the hot spot. However, our main interest is in the HPHT synthesis experiments using the LHDAC facility, [16,17] and in these types of experiments, temperature estimation with error bars of ±100 K to ±300K [18][19][20] are routinely reported.…”