HIGH SENSITIVITY DETECTION OF CH AND OH RADICALS IN FLAMES USING WAVELENGTH MODULATION SPECTROSCOPY AND DIODE LASER-BASED UV LIGHT SOURCES

Author Institution: Southwest Sciences, Inc., Santa FeTunable, wavelength modulated 426 nm and 310 nm were developed by second harmonic generation of modulated 852 nm DBR diode laser and sum frequency mixing with $488 nm Ar^{-}$ laser output, respectively. The 426 nm beam was used to map CH radical distributions in ethylene/air diffusion flames using the $R_{2}(8)$ line in the (0,0) band of the $CHA\leftarrow X$ transition by high sensitivity wavelength modulation absorption spectroscopy (WMS). Absorbances of $4 \times 10^{-5}$ have been measured using second harmonic (2f) WMS with a signal-to-noise ratio of 3:1 in a 3 Hz measurement bandwidth. Concurrent 2f detection of CH LIF was also demonstrated in flames with high sensitivity and spatial resolution. The 310 nm beam was used to detect OH radicals in an ethylene/air flame using the $P_{2}(4)$ transition in the (0,0) band of the $OH A\leftarrow X$ transition. Using 2f WMS absorption detection, we achieved a minimum detectable absorbance of $3 \times 10^{-6}$ at a 1 Hz measurement bandwidth. Experimental results to date along with the feasibility of extending to shorter wavelengths to access other flame species including NO and $SO_{2}$ will be discussed