CAREER: Spatially Resolved, Continuous Monitoring of Transient Processes Using Novel Optical Sensors

该研究计划围绕两项技术展开，这两项技术都采用了钛蓝宝石激光器和新的波长扫描技术。更大一部分的努力是致力于氙的双光子直接吸收。在这项技术中，快速可调谐的紫外光被用来监测氙的吸收特征，就像可调谐的二极管激光器被用来监测近红外中的水吸收一样。然而，由于氙的双光子吸收是一个非线性过程，它只发生在激光辐照度高的地方。因此，在聚焦激光束中，该过程仅发生在光束焦点附近，而不是沿着整个光束路径。该特性被用于扩展标准的直接吸收技术，以实现空间分辨率。线、平面或体的空间分辨率是通过使用振镜快速扫描激光焦点来完成的。该技术监测一个特性：氙数密度。然而，由于氙是惰性的，很容易在各种环境中播种，所以氙的数量密度信息比表面上看起来要有用得多。例如，只要压力已知，气体温度就可以通过氙数密度计算出来。此外，在混合实验中，通过将氙气注入多种流体中的一种，氙气甚至可以通过改变其成分的化学反应来跟踪该流体。第二种技术使用新的波长扫描方法来监测拉曼散射光谱。该技术以较低的信号水平为代价，提供了更多的特性信息（例如，多种物种的同时浓度），从而补充了氙气技术。描述了与燃烧有关的液体和喷雾系统的应用。虽然燃烧传感是主要的兴趣，这两种技术预计是有价值的传感在其他环境中。制定了未来五年的研究和教学计划，旨在为未来的努力奠定坚实的基础。该研究计划扩展了PI开发的新的激光波长扫描概念，以提供前所未有的连续，空间分辨的气体和液体特性测量。这些数据是在与燃烧相关的基础和应用系统中获得的，其目标是显著提高对控制过程的理解。该研究启发了将主动学习技术纳入本科热流体科学课程。通过传统的以讲座为基础的形式，这些技术旨在培养创造性思维和对课程材料的物理熟悉度。概念量表用于指导和评估主动学习练习。此外，本科研究人员（包括代表性不足群体的学生），光学技术研究生班和外展活动都与研究计划相结合。

Intellectual meritThe research plan is centered around two techniques, both of which employ a Ti:sapphire laser and new wavelength-scanning techniques. A larger portion of the effort is devoted to two-photon direct absorption of xenon. In this technique, rapidly tunable ultraviolet light is used to monitor a xenon absorption feature in much the same way tunable diode lasers have been used to monitor water absorption in the near infrared. However, because the two-photon absorption in xenon is a nonlinear process, it occurs only where laser irradiance is high. Thus, in a focused laser beam, the process occurs only near the beam focus and not along the entire beam path. This property is exploited to extend standard direct-absorption techniques to enable spatial resolution. Spatial resolution in a line,plane, or volume are accomplished by rapidly scanning the laser focus through space using galvanometers. The technique monitors one property: xenon number density. However, because xenon is inert and easy to seed in a variety of environments, xenon number-density information is much more useful than it might seem on the surface. For instance, whenever pressure is known, gas temperature can be calculated from the xenon number density. In addition, by seeding xenon into one of multiple fluids in a mixing experiment, the xenon can be used to track that fluid even through chemical reactions that change its composition. The second technique uses new wavelength-scanning approaches to monitor Raman scattering spectra. This technique complements the xenon technique by offering more property information (e.g., simultaneous concentrations of multiple species) at the cost of lower signal levels. Applications in liquid and spray systems relevant to combustion are described. Although combustion sensing is of primary interest, both techniques are expected to be valuable for sensing in other environments as well.Broader impactA research and teaching plan for the next five years is laid out, designed to build a firm foundation future efforts. The research plan extends new laser wavelength-scanning concepts developed by the PI to provide continuous, spatially resolved gas and liquid property measurements of an unprecedented nature. Such data are obtained in fundamental and applied systems relevant to combustion, with the goal of dramatically improving the understanding of the governing processes. The research inspires the inclusion of active learning techniques into the undergraduate thermal-fluid science curriculum. Balanced by a traditional lecture-based format, these techniques are intended to foster creative thinking and physical familiarity with course material. Concept inventories are used to guide and assess the active learning exercises. In addition, undergraduate researchers (including students of under-represented groups), a graduate class in optical techniques, and outreach activities are integrated with the research program.