[论文解读] Fast Switching Dual Fabry-Perot Cavity Optical Refractometry - Methodologies for Accurate Assessment of Gas Density

Isak Silander, Thomas Hausmaninger+3 more|arXiv (Cornell University)|Apr 3, 2017

Spectroscopy and Laser Applications被引用 5

一句话总结

本文提出了一种快速切换双法布里-珀罗腔光学折射率测量技术（FS-DFPC-OR），通过使用两个激光锁模腔体并进行快速顺序测量，消除了由腔体漂移引起的气体密度和流量测量误差。该技术可在开放系统和密闭系统中实现精确、无漂移的测量，即使在未进行温度稳定化处理的条件下也表现良好，具有极低的温度依赖性以及对微小泄漏的高灵敏度。

ABSTRACT

Dual Fabry-Perot cavity based optical refractometry (DFPC-OR) has a high potential for assessments of gas density. However, drifts of the FP cavity often limit its performance. We show that by the use of two narrow-linewidth fiber lasers locked to two high finesse cavities and Allan-Werle plots that drift-free DFPC-OR can be obtained for short measurement times (for which the drifts of the cavity can be disregarded). Based on this, a novel strategy, termed fast switching DFPC-OR (FS-DFPC-OR), is presented. A set of novel methodologies for assessment of both gas density and flow rates (in particular from small leaks) that are not restricted by the conventional limitations imposed by the drifts of the cavity are presented. The methodologies deal with assessments in both open and closed (finite-sized) compartments. They circumvent the problem with volumetric expansion, i.e. that the gas density in a measurement cavity is not the same as that in the closed external compartment that should be assessed, by performing a pair of measurements in rapid succession; the first one serves the purpose of assessing the density of the gas that has been transferred into the measurement cavity by the gas equilibration process, while the 2nd is used to automatically calibrate the system with respect to the relative volumes of the measurement cavity and the external compartment. The methodologies for assessments of leak rates comprise triple cavity evacuation assessments, comprising two measurements performed in rapid succession, supplemented by a 3rd measurement a certain time thereafter. A clear explanation of why the technique has such a small temperature dependence is given. It is concluded that FS-DFPC-OR constitutes a novel strategy that can be used for precise and accurate assessment of gas number density and gas flows under a variety of conditions, in particular non-temperature stabilized ones.

研究动机与目标

• 解决双法布里-珀罗腔折射率测量中因腔体漂移导致的性能限制。
• 实现在未进行温度稳定化环境下的精确气体密度与流量评估。
• 通过成对测量确定相对体积，解决密闭腔体中体积膨胀带来的挑战。
• 开发基于三腔体抽空技术的微小气体泄漏检测方法。
• 通过内在设计与校准，最小化折射率测量中的温度依赖性。

提出的方法

• 利用两个线宽窄的光纤激光器锁定至高精细度法布里-珀罗腔体，实现稳定、无漂移运行。
• 通过在两种测量状态间快速切换：一种用于气体平衡，另一种用于系统校准。
• 应用Allan-Werle图验证在短测量时间内无漂移性能。
• 执行一对连续测量，以确定测量腔体与外部腔室之间的相对体积比。
• 采用三重测量协议——两次快速连续测量后接一次延迟后的第三次测量——以评估泄漏速率。
• 利用双腔体配置的固有温度不敏感性，降低热漂移影响。

实验结果

研究问题

• RQ1 如何在双法布里-珀罗腔折射率测量中有效抑制腔体漂移，以实现精确的气体密度测量？
• RQ2 何种测量策略可实现对密闭、有限体积腔室中气体数密度的精确评估，即使存在体积膨胀？
• RQ3 如何利用光学折射率测量实现对微小气体泄漏的高灵敏度检测？
• RQ4 所提出系统中低温度依赖性的来源是什么，其如何被用于实现稳定运行？
• RQ5 该方法是否可在无需温度稳定化的情况下实现高精度测量？

主要发现

• FS-DFPC-OR方法在短测量时间内实现了无漂移运行，Allan-Werle图结果已证实。
• 通过一对快速连续测量校准体积比，该技术可精确测定开放系统和密闭系统中的气体数密度。
• 通过包含两次快速测量和一次延迟测量的三腔体抽空协议，实现了对泄漏速率的高灵敏度评估。
• 由于两个激光锁模腔体的差分响应，系统表现出极低的温度依赖性，从而内在补偿了热漂移。
• 该方法在未进行温度稳定化条件下依然有效，适用于现场与工业应用。
• 该方法可实现对气体流量（尤其是微小泄漏）的精确且准确的评估，且无需预先知晓系统几何结构。