Investigation of SO sub(3) absorption line for in situ gas detection inside combustion plants using a 4-[mu]m-band laser source

We have investigated 4-[mu]m-band SO sub(3) absorption lines for in situ SO super(3) detection using a mid-infrared laser source based on difference frequency generation in a quasi-phase-matched LiNbO sub(3) waveguide. In the wavelength range of 4.09400-4.10600 [mu]m, there were strong SO sub(3) absorption lines. The maximum absorption coefficient at a concentration of 170 ppmv was estimated to be about 3.2x10 super(-5) cm super(-1) at a gas temperature of 190[degrees]C. In coexistence with H super(2), the reduction of the SO sub(3) absorption peak height was observed, which was caused by sulfuric acid formation. We discuss a method of using an SO sub(3) equilibrium curve to derive the total SO3 SO3 molecule concentration.