Fiber Laser Based Mid-Infrared, Wavelength-Agile Sensor for Monitoring Trace Gas Concentrations in Harsh Environments

基于光纤激光器的中红外波长灵活传感器，用于监测恶劣环境中的痕量气体浓度

• 批准号: 0307455
• 负责人: Scott Sanders
• 金额: --
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-07-01 至 2007-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0307455&HistoricalAwards=false
• 关键词: Fiber; Laser; Based; Mid; Infrared

This project develops an all-fiber-optic sensor for measuring trace-gas concentrations (in the range of 1 - 10,000 ppm) in harsh environments such as piston and aeropropulsion engines. The sensor uses mid-infrared absorption spectroscopy to probe transitions in the fundamental vibrational bands of the target gases. The sensor accesses strong carbon-monoxide transitions near 4.85 mm, and has the potential to tune throughout the 1.6 - 7.5 mm spectral range; it can also access a host of other gases including nitric oxide (5.2 mm), nitrogen dioxide (6.1 mm), nitrous oxide (4.5 mm), sulfur dioxide (7.2 mm), hydrocarbons (3.4 mm) and a variety of radical species. Many of these important species are difficult to access in other spectral ranges; for example, electronic CO transitions exist only in the vacuum ultraviolet and are therefore impossible to access by single-photon techniques. The heart of the proposed sensor is an all-fiber-optic source for generating rapid wavelength scans in the mid-infrared. The development of such a source is a significant portion of the proposed work. The "wavelength-agile" source scans through approximately 100 nm every 20 ns. This source consists of three elements connected in series: an ultrafast fiber laser operating near 1.56 mm, a nonlinear wavelength-conversion element for shifting the ultrafast pulses to the mid-infrared, and a chirped fiber Bragg grating for arranging the mid-infrared pulses into rapid wavelength scans. To measure trace-gas concentrations, the wavelength-agile output is fiber-coupled to the environment of interest (such as an engine), and the transmitted light is monitored by a small-area infrared detector. In this fashion, a 100-nm-wide absorption spectra can be obtained every 20 ns. Consecutive absorption spectra can be averaged to improve sensitivity; depending on the application and the trace-gas concentration, 10 - 10,000 averages may be used to obtain absorption spectra every 0.2 - 200 ms. Each absorption spectrum is reduced to gas concentration, enabling the sensor to continuously monitor trace gases at sufficiently high rates to track most transient chemical phenomena. The sensor capabilities can be extended by using the same ultrafast fiber laser to generate both mid-infrared, as described in this proposal, and near-infrared, using techniques recently developed by the investigator. Such a sensor can monitor the concentrations of minor and major species as well as gas temperature and pressure in harsh environments.Measurements such as these have been generally unavailable owing to the high pressures, high temperatures, and multiple abundant species present in these environments. However, emerging fiber-optic technology not only offers a solution to this sensing challenge, but also provides the potential for very compact, handheld trace-gas sensors. Sensing of carbon monoxide (CO) is emphasized here because of the associated health effects, regulatory standards, and relevance to fundamental chemical problems in combustion, fuel reforming, and other processes.

该项目开发了一种全光纤传感器，用于测量活塞和航空推进发动机等恶劣环境中的痕量气体浓度（范围为1 - 10，000 ppm）。 该传感器使用中红外吸收光谱来探测目标气体的基本振动带中的跃迁。 该传感器可在4.85 mm附近获得强的一氧化碳跃迁，并有可能在1.6 - 7.5 mm光谱范围内进行调谐;它还可以获得许多其他气体，包括一氧化氮（5.2 mm），二氧化氮（6.1 mm），一氧化二氮（4.5 mm），二氧化硫（7.2 mm），碳氢化合物（3.4 mm）和各种自由基物质。 这些重要的物种中有许多在其他光谱范围内很难获得;例如，电子CO跃迁只存在于真空紫外线中，因此不可能通过单光子技术获得。 该传感器的核心是一个全光纤光源，用于在中红外波段产生快速波长扫描。开发这样一个源是拟议工作的一个重要部分。 “波长敏捷”光源每20 ns扫描约100 nm。 该光源由串联的三个元件组成：工作在1.56 mm附近的超快光纤激光器、用于将超快脉冲转换为中红外的非线性波长转换元件以及用于将中红外脉冲排列的啁啾光纤布拉格光栅。快速波长扫描。为了测量痕量气体浓度，波长捷变输出光纤耦合到感兴趣的环境（如发动机），并通过小面积红外探测器监测透射光。 以这种方式，可以每20 ns获得100 nm宽的吸收光谱。 可以对连续吸收光谱求平均值以提高灵敏度;根据应用和痕量气体浓度，可以使用10 - 10，000个平均值以每0.2 - 200 ms获得吸收光谱。每个吸收光谱被减少到气体浓度，使传感器能够以足够高的速率连续监测痕量气体，以跟踪大多数瞬态化学现象。 传感器的能力可以通过使用相同的超快光纤激光器来扩展，以产生中红外，如本提案所述，以及近红外，使用研究人员最近开发的技术。 这种传感器可以监测恶劣环境中的次要和主要物质的浓度以及气体温度和压力。由于这些环境中存在高压，高温和多种丰富的物质，因此通常无法进行诸如此类的测量。 然而，新兴的光纤技术不仅为这一传感挑战提供了解决方案，而且还为非常紧凑的手持式痕量气体传感器提供了潜力。这里强调一氧化碳（CO）的传感，因为相关的健康影响，监管标准，并在燃烧，燃料重整和其他过程中的基本化学问题的相关性。