PULSED ABSORPTION DIFFRACTOMETER FOR DETECTING TRACE SPECIES

WITH THE INCREASE IN ATMOSPHERIC POLLUTION AND A NEW, GROWING PUBLIC AWARENESS OF RESULTING ENVIRONMENTAL DAMAGE, THERE IS A NEED FOR NEW TECHNOLOGY TO MEASURE THE CONCENTRATION OF TRACE SPECIES IN THE ATMOSPHERE. EXTRACTIVE METHODS, IN WHICH A SEALED SAMPLE OF AIR IS ANALYZED IN A LABORATORY, ARE EXPENSIVE AND INAPPLICABLE TO CONTINUOUS, IN SITU MONITORING OF CONCENTRATIONS. THE DEVELOPMENT OF AN INSTRUMENT CALLED A PULSED ABSORPTION DIFFRACTOMETER (PAD) IS BEING DEVELOPED TO FILL THIS NEED. THE BASIS OF THIS INSTRUMENT IS THE DETECTION OF A TRANSIENT, VOLUMETRIC DIFFRACTION GRATING THAT IS FORMED AFTER A PULSED LASER BEAM IS ABSORBED BY TRACE SPECIES PRESENT IN THE ILLUMINATED REGION. THE PAD IS SENSITIVE TO PARTS-PER-TRILLION TRACE-GAS CONCENTRATIONS, 2-3 ORDERS OF MAGNITUDE BETTER THAN INSTRUMENTS BASED ON OTHER APPROACHES TO MONITOR TRACE SPECIES IN THE FIELD.