Measuring weak water vapour absorption using a supercontinuum source (MASS)

使用超连续谱源 (MASS) 测量弱水蒸气吸收

基本信息

批准号：
ST/M000281/1
负责人：
Keith Shine
金额：
$ 1万
依托单位：
University of Reading
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2015
资助国家：
英国
起止时间：
2015 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=ST%2FM000281%2F1
关键词：
Measuring weak water vapour absorption

项目摘要

MASS is a proof-of-concept proposal to assess the potential of coupling a super-continuum light source (SCLS) to a Fourier Transform Spectrometer (FTS) to achieve high-precision molecular spectroscopy. The proposed pilot application is to make new measurements of the weak (continuum) absorption of water vapour in the 1.6 micron near-infrared window in atmospheric conditions, which, if successful, would lead to a major advance in our understanding of the nature of that absorption. The work has a much wider relevance to improved measurements at other wavelength and to the characterisation of a wide range of weak absorption by other gases and particulates of importance in spectroscopy, atmospheric and planetary science and environmental monitoring.The work falls in the "Environment" priority area of the Global Challenges call. It is of direct relevance to the "water", "monitoring" and "underpinning of climate system modelling" sub-themes. It links atmospheric science expertise at the University of Reading and the laboratory-based molecular spectroscopy expertise at the STFC Rutherford Appleton Laboratory Molecular Spectroscopy Facility.SCLS are a new compact way of generating "white" light. SCLS offers unique advantages that can strongly benefit the field of high resolution precision spectroscopy using FTS. They could replace the traditionally-used incandescent lamps. Features include:(1) Brightness: Incandescent lamps are rather inefficient in delivering broadband light. SCLS are far brighter sources (about three orders of magnitude at wavelengths of 1.6 micron compared to traditional lamps) which maintain a broadband nature. If a detector-limited FTS with the required dynamic range is assumed, the brightness benefits turns directly into a signal to noise ratio improvement on the recorded spectra.(2) Spatial coherence: Unlike lamps, SCLS are spatially coherent sources in a similar way to laser light. This fundamental difference brings unique propagation benefits to be exploited in precision molecular spectroscopy. One way to improve spectrometer sensitivity consists of increasing the interaction length between the sample and light. With incoherent light such as emitted by lamps, the number of passes remains limited to typically ~15 passes (in a muli-pass cell). Owing to far better propagation characteristics, coherent light from SCLS can be more effectively folded with passes of 40-200 possible. (3) Noise of SCLS: Due to the complexity of non-linear effects producing the super continuum, noise properties of SCLS are still being researched. They are fundamentally noisy sources that can nevertheless approach the ideal realization of a low-noise coherent source when the source driving parameters are optimized. Previous work suggests that source power referencing is necessary to achieve detector limited spectroscopy and fully benefit from the SCLS power advantage.The application of the new system proposed here is the improved characterisation of the near-infrared continuum absorption due to water vapour. The unstructured continuum absorption due to water vapour is of most importance in atmospheric science in the "windows" between the rotation and vibration-rotation bands of water vapour. These windows are also widely used in remote sensing to derive the properties of the Earth's surface, clouds and atmospheric aerosols, for which water vapour absorption acts as an interference that must be removed for robust retrieval of the properties of interest. The focus here is on the 1.6 micron window as recent near-room-temperature absorption measurements using a variety of techniques disagree by orders of magnitude, and there is limited understanding of the temperature dependence.

MASS 是一项概念验证提案，旨在评估将超连续谱光源 (SCLS) 与傅里叶变换光谱仪 (FTS) 耦合以实现高精度分子光谱的潜力。拟议的试点应用是对大气条件下 1.6 微米近红外窗口中水蒸气的弱（连续）吸收进行新的测量，如果成功，将导致我们对水蒸气本质的理解取得重大进展。吸收。这项工作与改进其他波长的测量以及表征光谱学、大气和行星科学以及环境监测中重要的其他气体和颗粒物的广泛弱吸收具有更广泛的相关性。这项工作属于“环境”全球挑战呼吁的优先领域。它与“水”、“监测”和“气候系统建模的基础”直接相关。它将雷丁大学的大气科学专业知识与 STFC 卢瑟福阿普尔顿实验室分子光谱设施的实验室分子光谱专业知识联系起来。SCLS 是一种产生“白”光的新型紧凑方式。 SCLS 具有独特的优势，可以极大地有益于使用 FTS 的高分辨率精密光谱领域。它们可以取代传统使用的白炽灯。特点包括： (1) 亮度：白炽灯在提供宽带光方面效率相当低。 SCLS 是明亮得多的光源（与传统灯相比，在 1.6 微米波长下大约高出三个数量级），并且保持了宽带特性。如果假设探测器限制 FTS 具有所需的动态范围，则亮度优势将直接转化为记录光谱的信噪比改进。(2) 空间相干性：与灯不同，SCLS 是空间相干源，其方式类似于激光。这种根本性的差异带来了独特的传播优势，可在精密分子光谱中加以利用。提高光谱仪灵敏度的一种方法是增加样品与光之间的相互作用长度。对于非相干光（例如灯发出的光），通过次数通常仍限制在约 15 次（在多程池中）。由于具有更好的传播特性，SCLS 的相干光可以通过 40-200 次更有效地折叠。 (3)SCLS的噪声：由于产生超连续谱的非线性效应的复杂性，SCLS的噪声特性仍在研究中。它们本质上是噪声源，但是当源驱动参数优化时，它们可以接近低噪声相干源的理想实现。先前的工作表明，源功率参考对于实现探测器有限光谱并充分受益于 SCLS 功率优势是必要的。这里提出的新系统的应用是改进水蒸气引起的近红外连续吸收的表征。水蒸气引起的非结构化连续吸收在大气科学中最重要的是水蒸气旋转带和振动旋转带之间的“窗口”。这些窗口还广泛用于遥感，以获取地球表面、云和大气气溶胶的特性，其中水蒸气吸收充当干扰，必须将其消除，以便可靠地检索感兴趣的特性。这里的重点是 1.6 微米窗口，因为最近使用各种技术进行的近室温吸收测量在数量级上不一致，并且对温度依赖性的了解有限。