Collaborative Research: Development of a Diode Laser Cavity-Ringdown Spectrometer for Shipboard Measurements of the Stable Isotopes on Oceanic Methane

PIS提议开发一种腔衰荡光谱仪(CRDS)，能够在研究船上测量甲烷浓度和稳定同位素(ä2H-CH4和ä13C-CH4)，其精度可与标准实验室技术相媲美。已研制出便携式样机，测量重复性达到0.01%的标准误差。这意味着灵敏度为4 ppb，同位素精度类似于使用同位素所达到的水平。这一“基本”原型将被推进，以使其在舰载研究中更加稳健。主要的设计改进包括：1)通过外壳和绝缘增强热和振动隔离；2)通过集成声光调制器、半导体光放大器和多个激光器来提高采样率；3)使用调频光谱锁定吸收峰的能力；以及4)通过购买可以光纤耦合在一起的组件来最大限度地降低对错位的敏感性。将开发一种前端采样器，从充满海水、沉积物或游离气体的血清小瓶中自动提取甲烷，并将其注入分析腔中。拥有一台现场便携式仪器，可以对ä2H-CH4和ä13C-CH4进行高精度测量，将在海洋研究的许多领域(如极端环境中的生命、气候变化、石油研究、碳循环)有用。DL-CRDS将允许进行几乎无限数量的分析，极大地增强对正在研究的任何CH4系统的了解，而且由于这些测量是基于船舶的，也可用于指导同一探险期间的后续采样。广泛影响：这项提议旨在开发一种革命性的新测量系统，用于甲烷的稳定同位素。如果该系统能够成功地在远洋轮船上运行，那么将产生的甲烷数据量将出现潜在的爆炸性增长，并有望相应地增加对全球甲烷预算汇和来源的了解。基于光学光谱学(多个半导体激光光源耦合到一个高精度腔以实现高灵敏度和快速的CRDS测量方案)的甲烷同位素比值测量装置的实现将引起环境科学研究实验室的极大兴趣。该项目将培养博士后、研究生和本科生，并将加强跨学科伙伴关系。结果将向更广泛的科学受众传播，并将实现对地理问题的更好了解。

The PIs propose to develop a Cavity-Ringdown Spectrometer (CRDS) capable of measuring methane concentration and stable isotopes (ä2H-CH4 and ä13C-CH4) on a research vessel with a precision comparable to standard laboratory techniques. A portable prototype has been developed that has achieved a measurement reproducibility of 0.01 % standard error. This translates to a sensitivity of 4 ppb and an isotopic precision similar to what is achieved using Isotope. This "bare-bones" prototype will be advanced to make it more robust for ship-based research. The principal design modifications include: 1) increased thermal and vibrational isolation with caging and insulation, 2) increased sampling rates by incorporating acousto-optic modulators, semiconductor optical amplifiers, and multiple lasers, 3) the ability to lock onto an absorption peak using FM spectroscopy, and 4) minimized susceptibility to misalignment by purchasing components that can be fiber optically coupled together. A front-end sampler will be developed to automatically extract CH4 from an array of serum vials filled with seawater, sediment, or free gas and inject it into the analysis cavity.Having a field-portable instrument that can make high-precision measurements of ä2H-CH4 and ä13C-CH4 will be useful in many areas of oceanographic research (e.g. life in extreme environments, climate change, petroleum research, carbon cycling A DL-CRDS will allow a nearly limitless number of analyses to be conducted, greatly enhancing the understanding of any CH4 system under investigation and since these measurements are ship-based, can also be used to guide subsequent sampling during the same expedition.Broader Impacts: This proposal is aimed at developing a revolutionary new measurement system for the stable isotopes of methane. If the system can be successfully developed to work on ocean-going vessels, then there will be a potential explosion in the amount of methane data that will be produced and, hopefully, a corresponding increase in the understanding of methane budgets sinks and sources worldwide. The realization of a user-friendly and compact device based on optical spectroscopy (several diode laser sources coupled to a high finesse cavity for a high sensitivity and fast CRDS measurement scheme) for methane isotopic ratios measurement will present a high interest for research laboratories in environmental sciences. This Project will train post-docs, graduated and undergraduate students and it will enhance cross disciplinary partnerships. The results will be disseminated to a wider scientific audience and a better understanding of geographical problems will be achieved.