A DIODE LASER SENSOR FOR MEASUREMENT OF HYDROGEN CHLORIDE GAS

LARGE QUANTITIES OF TOXIC HYDROGEN CHLORIDE (HCL) GAS ARE EMITTED DURING SOME MISSILE LAUNCHES, POSING A SERIOUS SAFETY HAZARD TO LAUCH SITE PERSONNEL. EXISTING INSTRUMENTATION FOR MEASURING HCL CONCENTRATIONS DOES NOT HAVE ADEQUATE TIME RESPONSE OR SENSITIVITY, AND IS SUSCEPTIBLE TO INTERFERENCES FROM OTHER MISSILE EXHAUST GASES. WE PROPOSE A NEW INSTRUMENTATION CONCEPT FOR LAUNCH SITE MEASURMENT OF HCL, BASED ON ABSORPTION OF NEAR-INFRARED RADIATION FROM LOW-COST, COMMERCIAL INGAASP LASER DIODES. ADVANTAGES OF THE LASER DIODE MONITOR INCLUDE HIGH SENSITIVITY ACROSS THE FULL RANGE OF EXPECTED HCL CONCENTRATIONS, FAST TIME RESPONSE, SIMPLE CALIBRATION, AND COMPATIBILITY WITH FIBER OPTICES. THE UNDERLYING CONCEPTS OF THIS APPROACH WILL BE TESTED IN PHASE I USING LABORATORY BREADBOARD INSTRUMENTATION. THESE TESTS WILL EMPHASIZE EVALUATIONS OF SENSITIVITY, ACCURACY, AND CALIBRATION STABILITY. WE BELIEVE THAT COMPACT AND RELIABLE INSTRUMENTATION BASED ON THIS CONCEPT CAN BE DEVELOPED EITHER AS A SELF-CONTAINED PACKAGE FOR UNTENDED OPERATION, OR AS A FIBER-OPTIC NETWORK OF LOW-COST INSTRUMENTS FOR CENTRALIZED MONITORING OF HCL CONCENTRATIONS AT CRITICAL LOCATIONS.