直接测量金刚石对顶砧中流体压力-体积-温度状态方程的全光学方法
All-optical method to directly measure the pressure-volume-temperature equation of state of fluids in the diamond anvil cell
AI总结：
本研究提出一种结合共聚焦显微镜、白光干涉与新型密度-折射率自洽分析的全光学方法，可直接测量金刚石对顶砧中流体及透明固体的PVT状态方程，经多样品验证误差可控且具备优化空间。
摘要：
我们开发了一种新型全光学方法，通过测量样品腔的体积，直接测定金刚石对顶砧高压腔中流体及透明固体的压力-体积-温度（PVT）状态方程（EOS）。该方法将共聚焦显微镜与白光干涉技术相结合，并采用了一种利用样品密度与折射率相互依赖关系的新型分析方法：在实验中，折射率决定了测得的样品腔厚度（进而决定测得的样品体积/密度），而样品密度是决定折射率随压力变化的最主要因素。我们的分析方法能够得到一组密度与折射率的取值，二者相互自洽，且与实验数据在误差范围内吻合。我们在多种样品（H₂O、CH₄、C₂H₆、C₃H₈、KCl和NaCl）上开展了概念验证实验，实验条件包括环境温度，以及最高略高于500 K的高温。我们的概念验证数据表明，该方法能够在误差范围内复现已知的流体和固体状态方程。此外，我们证明该方法可直接、常规地测量简单流体在GPa级压力下的PVT状态方程，温度至少可达514 K（本研究达到的最高温度）。对体积测定中已知误差源的合理估算显示，目前高温下的误差为±2.7%，未来工作中有望将其降低至约±1%。
英文摘要：
We have developed a new all-optical method to directly measure the pressure-volume-temperature (PVT) equation of state (EOS) of fluids and transparent solids in the diamond anvil high pressure cell by measuring the volume of the sample chamber. Our method combines confocal microscopy and white light interference with a new analysis method which exploits the mutual dependence of sample density and refractive index: Experimentally, the refractive index determines the measured sample chamber thickness (and therefore the measured sample volume/density), yet the sample density is by far the dominant factor in determining the variation in refractive index with pressure. Our analysis method allows us to obtain a set of values for the density and refractive index which are mutually consistent, and agree with the experimental data within error. We have conducted proof-of-concept experiments on a variety of samples (H$_{2}$O, CH$_{4}$, C$_{2}$H$_{6}$, C$_{3}$H$_{8}$, KCl and NaCl) at ambient temperature, and at high temperatures up to just above 500 K. Our proof-of-concept data demonstrate that our method is able to reproduce known fluid and solid EOS within error. Furthermore, we demonstrate that our method allows us to directly and routinely measure the PVT EOS of simple fluids at GPa pressures up to, at least, 514 K (the highest temperature reached in our study). A reasonable estimation of the known sources of error in our volume determinations indicates that the error is currently $\pm$ 2.7% at high temperature, and that it is feasible to reduce it to ca. $\pm$ 1% in future work.
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