A TUNABLE ROOM TEMPERATURE INFRARED LASER FOR MEASURING ATMOSPHERIC POLLUTANTS

SOLID STATE LASER SOURCES CURRENTLY AVAILABLE FOR MEASURING GREENHOUSE GASES, COMBUSTION PRODUCTS, AND OTHER SPECIES ACROSS THE 3 TO 30 MICRON REGION ARE LEAD SALT DIODE LASERS WHICH OPERATE AT LIQUID NITROGEN TEMPERATURES. PRACTICAL PROBLEMS INCLUDE THE NEED FOR CRYOGENIC COOLING, ERRATIC TUNING BEHAVIOR, AND LIMITED AVAILABILITY OF SINGLE MODE DEVICES IN THIS REGION. THE OPPORTUNITY EXISTS TO APPLY INEXPENSIVE, ROOM TEMPERATURE DIODE LASERS WHICH ARE NOW READILY AVAILABLE WITH ENOUGH POWER TO DIRECTLY DRIVE A NONLINEAR DIFFERENCE-FREQUENCY INFRARED GENERATOR. THE FACTS THAT THE NEW DIODE LASERS PRODUCE ENOUGH POWER, ARE AVAILABLE WITH 10 MHZ LINEWIDTHS WITHOUT AN EXTERNAL CAVITY, ARE TUNABLE, AND ARE REMARKABLY EFFICIENT MAKE THIS APPLICATION AN IMMEDIATE OPPORTUNITY. THE PHASE I OBJECTIVES INVOLVE THE BASIC DEMONSTRATION OF GENERATING TUNABLE INFRARED IN THE 10 MICRON REGION USING DIODE LASERS AND A GALLIUM SELENIDE CRYSTAL WITH A UNIQUE OPTICAL DESIGN WHICH COMPENSATES FOR BEAM WALK-OFF AND PERMITS THE WIDE TUNABILITY OF AN ANGLE-TUNED SYSTEM WITH NEARLY THE SAME CONVERSION EFFICIENCY POSSIBLE IN A 90 DEGREES PHASE-MATCHED SYSTEM. THE CALCULATE 10 MICRON POWER OF 0.25 MICROWATTS WILL RESULT IN THE DESIRED ABSORPTION SENSITIVITY OF 10(-5)/CM IN ONE SECOND, USING A STANDARD 1 MM MERCURY CADMIUM TELLURIDE DETECTOR WITH A DETECTIVITY OF 4 X 10(10) AND A 0.6 METER LONG MULTIPASS CELL WITH A 100 METER PATH LENGTH.