DIODE-LASER-BASED SUM-FREQUENCY GENERATION OF TUNABLE WAVELENGTH-MODULATED UV-LIGHT FOR OH RADICAL DETECTION

Greater than 1.5 muW of tunable wavelength-modulated 308-nm radiation was generated by sum-frequency mixing of 90 mW of 835-nm diode-laser o utput and 1.5 W of 488-nm Ar+-laser output in a beta-barium metaborate crystal. Hydroxyl radicals formed in a discharge-flow reactor were de tected by use of the generated UV beam by direct absorption, wavelengt h-modulation absorption spectroscopy, and laser-induced fluorescence. Wavelength modulation with second-harmonic detection yielded an estima ted minimum detectable absorbance of 8.5 x 10(-6) at a 1-Hz bandwidth. This absorbance level corresponds to an OH detection sensitivity of 1 1.7 parts per trillion for a 1-m path length at 1 atm and 298 K.