Implementation and application of the peak scaling method for temperature measurement in the laser heated diamond anvil cell

Abstract

A new design for a double-sided high-pressure diamond anvil cell laser heating set-up is described. The prototype is deployed at beamline 12.2.2 of the Advanced Light Source at Lawrence Berkeley National Lab. Our compact design features shortened mechanical lever arms, which results in more stable imaging optics, and thus more user friendly and more reliable temperature measurements based on pyrometry. A modification of the peak scaling method was implemented for pyrometry, including an iterative method to determine the absolute peak temperature, thus allowing for quasi-real time temperature mapping of the actual hotspot within a laser-heated diamond anvil cell without any assumptions on shape, size, and symmetry of the hotspot and without any assumptions to the relationship between fitted temperature and peak temperature. This is important since we show that the relationship between peak temperature and temperature obtained by fitting the Planck function against the thermal emission spectrum averaged over the entire hotspot is not constant but depends on variable fitting parameters (in particular, the size and position of the fitting window). The accuracy of the method is confirmed through measuring melting points of metal wires at ambient pressure. Having absolute temperature maps in real time allows for more differentiated analyses of laser heating experiments. We present such an example of the pressure variations within a heated hotspot of AgI at a loaded base pressure of 3.8 GPa.

Measurements of thermal conductivity across the B1-B2 phase transition in NaCl

“…The temperature was measured using spectroradiometry techniques that obtain an average temperature for the entire hotspot, combined with a two-dimensional map of the hotspot intensity radial profile. [21][22][23] At each pressure step, the laser power was increased in 0.5 W steps. At each laser power, 2-5 separate temperature measurements were obtained.…”

Thermal Pressure in the Laser‐Heated Diamond Anvil Cell: A Quantitative Study and Implications for the Density Versus Mineralogy Correlation of the Mantle

“…This approach avoids the notorious chromatic aberration artifacts and also produces full absolute temperature maps in real time, thus enabling the spatial mapping of the thermal pressure effects presented here. System response was measured with a calibrated W‐lamp (Kunz et al, 2018). The system response does not include the effects of the diamond anvils as an optical element.…”

“…However, as shown by Benedetti et al (2007), diamonds influence the system response primarily through their strong index of refraction, which creates a strong chromatic aberration effect. Kunz et al (2018) and Rainey and Kavner (2014) document that the pyrometry setup employed at beamline 12.2.2 implicitly excludes any chromatic aberrations. Possible effects on the system response by differential absorption of the diamonds can be neglected due to the flat optical absorption response of CVD diamonds in the wavelength range of interest (Liang et al, 2009).…”

Carbide Formation in Refractory Mo15Nb20Re15Ta30W20 Alloy under a Combined High-Pressure and High-Temperature Condition

“…The technique of synchrotron radiation, combined with double-sided laser heating or resistive heating, has become a unique method for combined high-temperature and high-pressure studies [ 23 ]. The laser-heated diamond anvil cell (LHDAC) [ 24 , 25 , 26 ] has become an important tool, which can easily generate high pressure by compressing small samples between two opposing diamond culets. However, the lack of temperature measurement accuracy is an ongoing problem [ 25 ].…”

“…The laser-heated diamond anvil cell (LHDAC) [ 24 , 25 , 26 ] has become an important tool, which can easily generate high pressure by compressing small samples between two opposing diamond culets. However, the lack of temperature measurement accuracy is an ongoing problem [ 25 ]. Resistively heated diamond anvil cell (DAC) [ 27 ] controls the temperature by mounting an electrical heater with adjustable voltage and current out of the DAC body.…”