ATMOSPHERIC WATER-VAPOR PROFILER

THE AIR FORCE HAS EXPRESSED AN INTEREST IN BEING ABLE TO MEASURE THE CONCENTRATION OF WATER VAPOR, AND OTHER GASES, IN THE ATMOSPHERE AT ALTITUDES BETWEEN 15 AND 90 KM. THE MEASUREMENT WOULD BE CONDUCTED DURING THE DESCENT PHASE OF A SMALL ROCKET FLIGHT. IN THE PHASE I OF THIS RESEARCH EFFORT, WE PROPOSE TO MAKE SEVERAL MEASUREMENTS THAT WILL ALLOW US TO DESIGN A WATER-VAPOR DETECTOR BASED ON A DIODE-LASER-PUMPED SOLID-STATE LASER. WE WILL USE EITHER A THULIUM LASER, WHICH IS CONTINUOUSLY TUNABLE FROM 1.85 UM TO OVER 2 UM, OR AN ERBIUM LASER, WHICH HAS SEVERAL EMISSION LINES BETWEEN 2.6 UM AND 2.9 UM. THE LASER WILL BE ALTERNATELY TUNED ON AND OFF A STRONG ABSORPTION LINE, AND BOTH THE SHIFTED FLUORESCENCE EXCITED BY THE LASER, AND THE BACKSCATTERED LIGHT AT THE LASER WAVELENGTH WILL BE COLLECTED. AT HIGH ALTITUDES, BOTH SIGNALS WILL BE DUE TO WATER-VAPOR FLUORESCENCE, AND THE H2O CONCENTRATION WILL BE CALCULATED FROM THE INTENSITY. AT LOWER ALTITUDES, WHERE THE FLUORESCENCE IS QUENCHED, THE [H2O] WILL BE CALCULATED FROM THE DIFFERENCE IN THE BACKSCATTERED INTENSITY WHEN THE LASER IS TUNED ON OR OFF THE ABSORPTION PEAK. MEASUREMENTS OF THE H2O FLUORESCENCE QUANTUM YIELD AND RADIATIVE LIFETIME AS A FUNCTION OF PRESSURE, AND A DEMONSTRATION OF RAPID TUNING BETWEEN AN ABSORPTION PEAK AND MINIMUM WILL BE CONDUCTED. WE WILL ALSO EXAMINE APPROACHES BASED ON RAMAN SCATTERING AND FLUORESCENCE EXCITED BY ULTRA-VIOLET LIGHT. POTENTIAL APPLICATIONS INCLUDE SCIENTIFIC LASERS FOR SPECTROSCOPY, COMMERCIAL LASERS FOR PROCESS CONTROL, REMOTE SENSING OF AIR POLLUTANTS, AND BASIC INFORMATION USEFUL FOR THE MODELING OF THE CHEMISTRY OF THE UPPER ATMOSPHERE.