DEGENERATE 4-WAVE-MIXING IN NITROGEN-DIOXIDE - APPLICATION TO COMBUSTION DIAGNOSTICS

Single shot degenerate four wave mixing (DFWM) images of the distribution of nitrogen dioxide (NO2) doped into a propane/air flame at concentrations of the order of 7000 ppm have been obtained. These images indicate the relative concentration of NO2 in different parts of the flame with an estimated spatial resolution of 150-mu-m. Initial experiments were performed using NO2 in a glass cell with nitrogen buffer gas. DFWM signals were generated using both the frequency doubled output of a pulsed ND: YAG laser and the tunable blue output of an excimer pumped dye laser. The signal was investigated as a function of laser power, NO2 concentration and buffer gas pressure. In addition, spectra of NO2 in the region 450 to 480 nm were obtained. Signals were then sought in both a cold air/NO2 gas flow and an ignited mixture of propane and air seeded with NO2, using a DFWM imaging geometry. The resulting images from the flame demonstrate the disappearance of the NO2 molecules in the flame interaction zone.