Abstract
We show that a strategy for increased accuracy in temperature determination by optical pyrometry when the wavelength dependence of the emissivity is unknown is to measure the spectral irradiance at short wavelengths. We then introduce an improved method of determining the temperature in laser heated diamond anvil cells. In general a blackbody source is used to determine the optical transfer function required for determining the blackbody curve. By using the thermal radiation of a heated absorber at ambient pressure and known temperature, uncertainties in the temperature determination caused by the wavelength dependence of the emissivity of the heated absorber can be eliminated. Temperature determination reduces to a one-parameter fit to the blackbody curve rather than the usual two parameters (emissivity and temperature), leading to increased precision and accuracy.
Highlights
Laser heating in diamond anvil cells (DACs) is an important technique that allows the development of high temperature conditions at static high pressure and has been widely used in many disciplines [1]
Pressure and temperature are the two most important parameters to be determined in laser heated diamond anvil cell (LHDAC) experiments
Advances in the LHDAC technology have continued, e.g., [5,6,7,8,9], since its inception [10]; still the complexity of these measurements can lead to significant uncertainty in determining pressure and temperature
Summary
Laser heating in diamond anvil cells (DACs) is an important technique that allows the development of high temperature conditions at static high pressure and has been widely used in many disciplines [1]. In a laser heated diamond anvil cell (LHDAC) pressures of the order of 100 GPa and temperatures of several thousand Kelvin can be achieved. In this paper we consider the strategy for optimally determining temperature and a present a technique that can improve the accuracy and precision in temperature determination The advantage of this technique is demonstrated by experimental measurements using platinum to absorb the laser power. For temperature measurement by optical pyrometry the thermal irradiance from the absorber is collected as a function of wavelength; temperature is determined by fitting to the Planck thermal radiation function. In order to accurately determine the temperature, the BB lineshape, which is usually distorted by the measurement instruments, must be determined and the emissivity of the absorber must be known as a function of wavelength and temperature.
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