QUANTITATIVE DETECTION OF GAS-PHASE NAOH USING 355-NM MULTIPLE-PHOTONABSORPTION AND PHOTOFRAGMENT FLUORESCENCE

The third-harmonic output of a Nd:YAG laser is utilized in the quantit ative detection of gas-phase NaOH, Species selectivity and sensitivity are achieved via multiple-photon absorption and photodissociation of NaOH-in combination with monitoring of the subsequent Na photofragment fluorescence. Detection limits of similar to 0.5 ppm of gas-phase NaO H have been achieved under atmospheric conditions, The fluorescence in tensity has been found to be proportional to the square of the laser p ower, which is consistent with a second-order absorption process. Alth ough the technique is less sensitive than the more widely used excimer laser-induced photofragment fluorescence approach, there are many tec hnical advantages which make it more suitable for use in modern coal c ombustion systems, These combustion systems require accurate alkali me asurement and control to combat fouling and corrosion of process surfa ces and turbine blades.