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Measurements of Diffusion Rates of Liquids through Materials

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Final rept. 15 Sep 1989-14 Mar 1991

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The identification of molecular species is a very old problem which has been dealt adequately for samples in the solid, liquid and gas phases. Most analytical methods were performed in situ where a sample of the material to be analyzed is brought to the laboratory for analysis. Remote sensing is rather rare and more difficult to perform, especially at very low concentrations and in the case where the material must be distinguished form others of very similar structure. To achieve remote sensing of specific molecular structure we devised an experimental system and procedure which was based on thermal lensing and UV and Raman spectroscopy. Thermal lensing techniques rely upon effect of heat generated as the absorbed light decays into vibrational modes of the medium thermal lensing and fluorescence have been utilized to determine fluorescent and non-fluorescent substances to a concentration of about 10-11 M. We believe that thermal lensing is an ideal method for the detection of trace amounts of chemical and biological agents because it is a strictly remote method, requiring no contact with any instruments or personnel, can be operated in closed or open terrain and has the sensitivity to detect and distinguish small amounts of closely related molecular species.

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  • Atomic and Molecular Physics and Spectroscopy

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