The effects of chromatic dispersion on temperature measurement in the laser-heated diamond anvil cell

Abstract

We have developed numerical simulations of spectroradiometric temperature measurement for refractive optical systems used in laser-heated diamond anvil cell (LHDAC) experiments. Chromatic dispersion in refractive optics is quantified by the wavelength-dependent radial displacement function. Results show that a combination of high peak temperature, steep temperature gradient, high spatial resolution, and large radial displacement can cause extreme errors in temperature, on the order of hundreds to thousands of degrees of Kelvin. Increasing detector bin size can dampen the magnitude of the error in peak temperature, but the average temperature produced in this way is still likely to be erroneous. Accurate peak temperature can be measured if the radial displacement is less than the radius of a region of constant temperature. Errors in accuracy can be reduced by locating the wavelength range that produces a minimum and symmetrical radial displacement. The precision of the fitted blackbody function is correlated positively with accuracy so that the optimal wavelength range can be located by minimizing the error in the blackbody fit. Modern spectroradiometric systems that utilize refractive optics are capable of accurate temperature measurement if proper steps are taken to identify and mitigate the effects of chromatic dispersion.