23 September 2002 Diode laser analysis of the sealed enclosures of the Charters of Freedom
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We report the application of diode laser spectroscopy to the non-intrusive measurement of water vapor and helium content within the enclosures of the Charters of Freedom that were sealed by NBS approximately 50 years ago. The instrument was adapted from the Diode Laser Hygrometer, developed through the NASA Global Tropospheric Experiment program to make open-path water vapor measurements outside the NASA DC-8 research aircraft. Operating in the 1.4-micron wavelength region, laser wavelength scans of water vapor absorption lines enabled the determination of the moisture level and the amount of helium relative to air within the Charters enclousres (an indicator of enclosure leaks). These measurements revealed that at least five of the seven Charters of Freedom enclosures had not leaked since they were sealed approximately 50 years ago. The measurements also revealed that water vapor within these enclosures ranged from 29 to 55% greater than anticipated.
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Glen William Sachse, Glen William Sachse, Glenn S. Diskin, Glenn S. Diskin, Thomas A. Slate, Thomas A. Slate, George F. Tucker, George F. Tucker, Joseph C. Hickman, Joseph C. Hickman, James R. Podolske, James R. Podolske, Margaret Kelly, Margaret Kelly, } "Diode laser analysis of the sealed enclosures of the Charters of Freedom", Proc. SPIE 4817, Diode Lasers and Applications in Atmospheric Sensing, (23 September 2002); doi: 10.1117/12.453764; https://doi.org/10.1117/12.453764

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