In-situ and Real Time 2D Temperature Mapping Using 4 Color Pyrometry at the Beamline PSICHE, Synchrotron SOLEIL
Abstract
Laser heating in the diamond anvil cell (LH-DAC) usually produces substantial radial temperature (T) gradients, because of the gaussian profile of the beam and the conductive heat transfer in the sample, pressure medium and gasket. In addition, the way the laser is absorbed by the sample depends on its composition and thickness, surface roughness, isolation from the diamond, melting, etc. The combination and variation of all these parameters yield to spatial and temporal T instabilities. Accurately measuring the hot spot radial T distribution over time is definitely a plus for in-situ experiments and post-heating sample analysis.
Since the introduction of 4 color pyrometry for the LH-DAC by Campbell (2008) two-dimensional T mapping is now routinely available in several laboratories. The principle of the technique is to acquire images of the hot spot at four different wavelength simultaneously that are then correlated spatially. Following the gray body approximation, T and emissivity maps are obtained from Wien fits of the data for each pixel. Beyond 2D mapping and despite larger uncertainties, the method has several advantages over single-point spectroradiometry: it is truly achromatic (each wavelength is focused independently), the peak T can always be determined, it is insensitive to misalignment (no entrance pinhole) and dynamic changes in sample T can be observed in 2D, especially during melting. This is also an excellent diagnostic tool to minimize T gradients during a laser heating session, using beam shapers for example. We present here our own LH-DAC 4-color pyrometry development, designed to be used in conjunction with in-situ XRD. Long working distance and diffraction limited Schwarzshild objectives have been designed specifically for this application. The optical paths inside the 4 color boxes have been modified to increase flux. The result is a new tool for in-situ and real time 2D T mapping on synchrotron beamlines. Campbell, A. J., Measurement of temperature distributions across laser heated samples by multispectral imaging radiometry, Rev. Sci. Instrum. 79, 015108 (2008)- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR23D0133G
- Keywords:
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- 3919 Equations of state;
- MINERAL PHYSICS;
- 3924 High-pressure behavior;
- MINERAL PHYSICS;
- 3939 Physical thermodynamics;
- MINERAL PHYSICS;
- 3994 Instruments and techniques;
- MINERAL PHYSICS