Compact Isotopic Raman Multigas Trace Detection System

自发拉曼散射是一种简单且经过充分研究的过程，非常适合于化学分析。然而，虽然在商业系统中通常用于识别固体和液体中的分子物种，但很少有用于气体测量的解决方案，部分原因是需要一种强大的、光谱纯的激光光源。然而，紧凑而廉价的便携式化学气体分析仪将在工业过程控制、医疗诊断和危险检测中获得大量应用。目前的项目正在探索解决方案，使气体自发拉曼散射达到成熟的水平，使其能够用于消费级设备。利用普通激光二极管和通过反馈同时定义激光光谱纯度的工程多程光束几何结构来实施，所研究的技术可以检测包括同位素在内的痕量化学物质，即只在其同位素组成上不同的分子。这些努力的重点是实际相关的测量，如大气和呼吸检测，这可能为实现多功能和可广泛部署的“人造鼻子”铺平道路。该项目需要在光子学和量子物理研究的跨学科环境中培训研究生和本科生。由于其固有的简单性和通用性，自发拉曼散射非常适合于化学气体分析。然而，由于散射截面很小，这一过程通常需要增强方法，其中最著名的例子可能是表面增强拉曼散射。近年来，空腔、毛细管、中空纤芯光纤和珀塞尔增强拉曼散射等方法的复兴，其中一些方法已经显示出在百万分之几的浓度范围内的气体传感能力。拟议工作的主要目标是开发一种新的方法，预计将提供显著改进，特别是在十亿分之一范围内的检测极限，同时采用低成本紧凑型设计，所有组件都在室温下运行。这种新的方法是基于多通道腔集成作为外腔半导体激光器的一部分，是多模和高效的。该项目探索了创造工程电磁环境的方法，以优化拉曼散射光子的收集程度。它的目的是了解如何最有效地利用光学腔来提高自发拉曼散射的速率，从而有利于痕迹检测。该项目对腔量子电动力学研究和一般计量科学以及在同位素微量气体传感中的广泛应用具有影响。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Spontaneous Raman scattering is a simple and well-studied process that is ideally suited for chemical analysis. However, while routinely implemented in commercial systems to identify molecular species in solids and liquids, few solutions exist for the measurement of gases, due in part to the need for a powerful and spectrally pure laser source. Yet, a compact and inexpensive portable chemical gas analyzer would find a plethora of applications in industrial process control, medical diagnostics and hazards detection. The present project is exploring solutions to bring gaseous spontaneous Raman scattering to a level of maturity that could allow it to be used in consumer-level devices. Implemented with an ordinary laser diode in conjunction with an engineered multi-pass beam geometry that simultaneously defines the laser’s spectral purity via feedback, the technique investigated can detect trace chemicals including isotopologues, i.e., molecules that differ only by their isotopic composition. These efforts are focusing on practically relevant measurements such as atmospheric and breath detection that could pave the way for the realization of versatile and widely deployable “artificial noses”. The project entails training graduate and undergraduate students in an interdisciplinary environment of photonics and quantum physics research. Due to its inherent simplicity and versatility, spontaneous Raman scattering is ideally suited for chemical gas analysis. However, with a small scattering cross-section, the process typically requires an enhancement method, of which the most famous example is probably surface enhanced Raman scattering. Recent years have seen a resurgence of approaches such as cavity, capillary, hollow core fiber, and Purcell-enhanced Raman scattering, some of which have demonstrated gas sensing capabilities in the parts-per-million concentration range. The primary goal of the proposed work is to develop a novel method expected to offer dramatic improvements, in particular, detection limits in the parts-per-billion range, while employing a low-cost compact design with all components operating at room temperature. The novel approach is based on a multi-pass cavity integrated as part of an external cavity diode laser that is multimode and efficient. The project explores methods of producing an engineered electromagnetic environment that optimizes the degree to which Raman scattered photons are collected. It aims at understanding how an optical cavity can be utilized most effectively to enhance the rate of spontaneous Raman scattering for the benefit of trace detection. The project has implications for cavity quantum electrodynamics research and general metrology science as well as a diverse range of applications in isotopologue trace gas sensing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.