Two thermooptic-based detection systems for gases were devel- oped and studied for their performances in monitoring air pollutants. In the first system which is based on the photoacoustic effect, a continuous-wave carbon dioxide laser was adapted for operation in the infrared with its output wavelength modulated between two consecutive vibration-rotation lines. This was accomplished by applying a time-varying electric field to a commercial piezoelectric pusher attached to the grating mount of the laser. Operating under wavelength modulation, the primary limitation on detectability in photoacoustic measurements--window absorption--was removed and the useful range for application was extended. This concept was illustrated by the determination of ppb levels of ethylene in nitrogen;In the second system, the feasibility of using Fabry-Perot interferometry for in situ trace detection of gases was studied. Two experiments were performed with a single frequency helium neon (HeNe) laser acting as a probe beam. The first one was based on a dual-beam arrangement, with direct measurement of the shift of interference fringe as a result of the change in refractive index caused by the absorption of excitation radiation by the species of interest. Because of certain instrumental limitations, the full potential of this scheme as a sensitive device for trace gas detection was never quite realized;The second Fabry-Perot interferometric experiment was based on a single-beam geometry using modulated excitation and coherent detection of the signal. A laboratory built position stabilization circuit was employed to maintain the interferometer at its optimum point of operation. By combining this with wavelength modulation, the;projected detection limit of the resulting scheme for C(,2)H(,4) in nitrogen was found to be 20 ppb (S/N = 3); (\u271)The Ames Laboratory is operated for the U.S Department of Energy by Iowa State University under contract No. W-7405-eng-82. This work was supported by the Office of Basic Energy Sciences.
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机译：开发了两个基于热光的气体检测系统，并研究了它们在监测空气污染物中的性能。在基于光声效应的第一个系统中，连续波二氧化碳激光器适用于在红外中工作，其输出波长在两条连续的振动旋转线之间进行调制。这是通过将时变电场施加到与激光器光栅架相连的商用压电推动器上来实现的。在波长调制下运行，消除了对光声测量中可检测性的主要限制（窗口吸收），并扩大了应用范围。通过测定氮气中乙烯的ppb水平来说明这一概念；在第二个系统中，研究了使用Fabry-Perot干涉仪进行气体原位痕量检测的可行性。使用单频氦氖（HeNe）激光作为探测光束进行了两个实验。第一个是基于双光束装置，直接测量干涉条纹的位移，该干涉条纹的位移是由感兴趣的物种吸收激发辐射而引起的折射率变化的结果。由于某些仪器的局限性，这种方案作为痕量气体检测的灵敏设备的全部潜力从未得到完全实现；第二次Fabry-Perot干涉测量实验基于使用调制激发和信号相干检测的单束几何结构。采用了实验室建立的位置稳定电路，以将干涉仪维持在最佳操作点。通过将其与波长调制相结合，发现在氮气中C（，2）H（，4）所得方案的预测检测限为20 ppb（S / N = 3）； （\ u271）艾姆斯实验室由爱荷华州立大学为美国能源部运营，合同编号为W-7405-eng-82。这项工作得到了基础能源科学办公室的支持。
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