A DIODE-LASER ABSORPTION REMOTE CONCENTRATION SENSOR

THE DIODE-LASER ABSORPTION REMOTE CONCENTRATION SENSOR (DARCS) WOULD HAVE NUMEROUS APPLICATIONS FOR MONITORING ATMOSPHERIC COMPOSITION IN THE FIRST KILOMETER ABOVE THE EARTH. IT COULD BE USED TO QUANTIFY CONCENTRATIONS OF MANY ATMOSPHERIC SPECIES, INCLUDING IMPORTANT MINOR CONSTITUENTS SUCH AS WATER AND CARBON DIOXIDE AND TRACE SPECIES SUCH AS CARBON MONOXIDE, NITRIC OXIDE, METHANE, HYDROGEN PEROXIDE, AND AMMONIA WITH HIGH ACCURACY, RAPID TIME RESPONSE, AND SENSITIVITIES BELOW THE LEVEL OF ONE PART PER MILLION. THE DARCS SYSTEM COULD BE READILY CONFIGURED FOR THESE OR OTHER ATMOSPHERIC SPECIES BY CHOOSING A NEAR-INFRARED DIODE SOURCEWITH A TUNING RANGE THAT OVERLAPS THE VIBRATIONAL SPECTRUM OF THE MOLECULE OF INTEREST. A SINGLE ABSORPTION LINE IS THEN MEASURED USING A DIODE-LASER OUTPUT THAT IS LOCKED TO AWAVELENGTH THAT EXACTLY MATCHES THE ABSORPTION WAVELENGTH. DARCS IS A SIMPLE, ROBUST, AND PORTABLE DEVICE CONSISTING OFAN OPTICAL TRANSCEIVER UNIT AND A DISTANT RETROREFLECTOR, WHICH DEFINE A LONG PATH ABSORPTION MEASUREMENT. IT COULD BE USED OVER A FIXED PATH LENGTH TO MONITOR THE AVERAGE COLUMN DENSITY WITH A TIME RESOLUTION OF LESS THAN 1 SECOND. ALTERNATIVELY, THE RETROREFLECTOR COULD BE MOUNTED ON A MOVING VEHICLE SUCH AS A BALLOON OR REMOTELY PILOTED AIRCRAFT TO MONITOR THE SPATIAL VARIATION IN THE ATMOSPHERICCONCENTRATION. PHASE I CONSISTS OF A SERIES OF EXPERIMENTS TO DEMONSTRATE THE OPERATION OF A BREADBOARD DARCS DEVICE CONTAINING TWO DIODE-LASER SOURCES LOCKED TO MOLECULAR ABSORPTION FEATURES OF TWO DIFFERENT ATMOSPHERIC MOLECULES.