Environmental applications of cavity enhanced spectroscopy in the mid infra-red region

腔增强光谱在中红外区的环境应用

• 批准号: NE/H019758/1
• 负责人: Andrew Orr-Ewing
• 金额: $ 8.53万
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Training Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FH019758%2F1
• 关键词: Environmental; applications; cavity; enhanced; spectroscopy

Ultrasensitive and quantitative absorption spectroscopy techniques will be developed in the mid infra-red region for determination of mixing ratios and isotopic abundances of trace atmospheric constituents. Technological developments based on recent work in the Bristol group will be exploited in a new generation of analytical spectrometers based on state-of-the-art laser technology in the infra-red at wavelengths beyond 3 microns. In this region, the strong fundamental vibrational transitions of a variety of molecules can be accessed spectroscopically, presenting considerable potential advantages of improved selectivity and detection limits over current instruments designed around telecoms diode lasers operating in the near infra-red. The project builds on: (a) our recent advances in cavity enhanced spectroscopy at 3.25 microns using efficient difference frequency generation (DFG) laser sources based on compact, low-cost diode lasers; and (b) an on-going project to couple a 7.8 micron quantum cascade laser (QCL) with an optical cavity using feedback of light to the laser to enhance the coupling efficiency. The PG student will focus on analytical and environmental applications. He/she will: (i) test the performance of an optical feedback cavity enhanced absorption spectroscopy (OF-CEAS) spectrometer with the 7.8 micron wavelength cw QCL laser (an apparatus being designed and built by a current PDRA, using existing equipment) by studying 13CH4 and 12CH4 absorption lines in close spectral proximity, and optimizing the precision and accuracy of determination of carbon isotope delta-13C values; (ii) couple the 3.2 micron wavelength DFG mid-IR spectrometer with a previously developed and automated pre-concentration apparatus (proven to be highly specific to ethene through use of a molecular sieve of appropriate pore size) to explore the feasibility of delta-13C determinations on C2H4 (present at less than a few ppbv in ambient air) as a proof-of-principle study; (iii) with the expertise gained from (i) and (ii), evaluate the potential for CEAS methods, coupled to pre-concentration stages if required, for isotopologue ratio measurements for a variety of further small compounds in air (e.g. N2O, C2H2); (iv) establish a collaboration with Prof R.P. Evershed (Chemistry, Bristol) and Dr E. Hornibrook (Earth Sciences, Bristol) to determine CH4 delta-13C values in studies of the effects of soil type and the role of methanotrophic bacteria on atmospheric methane; and (v) to explore the feasibility of deployment of a QCL-based spectrometer for in situ measurements of methane fluxes and their isotopic composition. Such delta-13C value determinations are a key means of establishing atmospheric sources and sinks, and a portable analytical spectrometer has considerable advantages of size, cost and ease of deployment over use of isotope ratio mass spectrometry if competitive accuracy and precision can be demonstrated. In addition to the regular academic, research and transferable skills training delivered through the Bristol Graduate School of Chemistry, the PG student will receive expert training in: lasers and molecular spectroscopy; optics and optical cavities; atmospheric and environmental chemistry; analytical spectroscopy; analysis of data sets; preparation of data for publication, etc. Within Bristol, the PG student will gain a broad perspective of the research area through interaction (e.g. joint group meetings and seminars) with the Atmospheric Chemistry Research Group headed by Prof D.E. Shallcross and Dr S. O'Doherty, the Organic Geochemistry Unit (led by Prof R.P. Evershed and Dr R.D. Pancost) and the cross-faculty Biogeochemistry Research Centre (encompassing groups from Chemistry, Biology, Earth Sciences, and Geography). The student will attend the European Research Course on Atmospheres (ERCA, held annually in Grenoble) and a planned workshop on Cavity Enhanced Spectroscopy (scheduled for 2011 in Canada).

将开发中红外区域的超灵敏和定量吸收光谱技术，用于确定微量大气成分的混合比和同位素丰度。基于布里斯托小组最近工作的技术发展将用于新一代分析光谱仪，该光谱仪基于波长超过3微米的红外线的最先进激光技术。在该区域，各种分子的强基本振动跃迁可以通过光谱进行访问，呈现出相当大的潜在优势，即比围绕在近红外中操作的电信二极管激光器设计的当前仪器具有更好的选择性和检测限。该项目的基础是：（a）我们最近在3.25微米处的腔增强光谱学方面的进展，其使用基于紧凑、低成本二极管激光器的高效差频产生（DFG）激光源;以及（B）一个正在进行的项目，其使用光到激光器的反馈来将7.8微米量子级联激光器（QCL）与光学腔耦合以提高耦合效率。PG学生将专注于分析和环境应用。他/她将：（i）测试具有7.8微米波长连续QCL激光器的光学反馈腔增强吸收光谱（OF-CEAS）光谱仪的性能（由当前PDRA使用现有设备设计和建造的装置），通过研究光谱接近的13 CH 4和12 CH 4吸收线，并优化碳同位素δ-13 C值测定的精确度和准确度;（ii）将3.2微米波长的DFG中红外光谱仪与先前开发的自动预浓缩装置耦合（通过使用适当孔径的分子筛证明对乙烯具有高度特异性），以探索C2 H4上δ-13 C测定的可行性（在环境空气中的浓度低于几ppbv）作为原理验证研究;（iii）利用从（i）和（ii）中获得的专门知识，评估CEAS方法的潜力，必要时结合预浓缩阶段，（iv）与R. P. Evershed教授（化学，布里斯托）及E. Hornibrook（地球科学，布里斯托），以确定土壤类型的影响和甲烷氧化细菌对大气甲烷的作用研究中的甲烷δ-13 C值;以及（五）探索部署QCL光谱仪现场测量甲烷通量及其同位素组成的可行性。这种δ-13 C值测定是确定大气源和汇的关键手段，如果能够证明具有竞争力的准确度和精确度，便携式分析分光计在尺寸、成本和易于部署方面比同位素比质谱法具有相当大的优势。除了通过化学的布里斯托研究生院提供定期的学术，研究和可转移的技能培训，PG学生将接受专家培训：激光和分子光谱学;光学和光学腔;大气和环境化学;分析光谱学;数据集分析;准备数据以供出版等。在布里斯托，PG学生将通过互动获得研究领域的广阔视野（例如联合小组会议及研讨会）与由D.E.教授领导的大气化学研究小组合作，Shallcross和S. O 'Doherty，有机地球化学单位（由R. P. Evershed教授和R.D. Pancost）和跨学院生物地球化学研究中心（包括化学，生物学，地球科学和地理学的团体）。学生将参加欧洲大气研究课程（ERCA，每年在格勒诺布尔举行）和腔增强光谱计划研讨会（定于2011年在加拿大）。