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Conventional methods for detecting the release of foreign substances into the atmosphere are often slow, expensive, and only give an actual reading for a small section of the area of interest. The Environmental Interferometer can allow inexpensive, real time monitoring of a large area. The principle behind the Environmental Interferometer is the use of a fringe locked Michelson Interferometer scanning throughout a continuous range of colors at an intermediate bandwidth (50-100 nm). The fringe locking allows a the beam in a test arm to be reflected through a test area for about 1 kilometer of distance, while a reference arm is kept in a controlled environment (perhaps fiber optics or a multiple reflected air path) and retain a suitable interference pattern. The use of intermediate bandwidth light allows the central fringe to be located, and thus allows fast scanning through a continuous range of colors. Sampling at n different colors allows the discrimination of n different sources of optical pathlength change. This allows easy discrimination against moisture content change, air turbulence, ground vibrations, and the like, because of their characteristic pathlength change frequencies. The fringe locking allows for the electronic interpretation of a signal and enhances the accuracy of the instrumentation so that small optical pathlength changes can be easily measured and interpreted. A demonstration unit has been created using a 670 nm laser instead of a filtered white light source. Absolute index measurements of test gases injected into a 3 cm pollution chamber were made with the demonstration unit with errors of less than 1%. The fringe locker used in the demonstration unit was able to keep the fringe pattern stable during table oscillations, moderately fast introduction of test gases, and simulated air turbulence.
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