CH radical distributions in ethylene–air and methane–air diffusion flames are mapped by wavelength-modulation absorption spectroscopy (WMS). Tunable, wavelength-modulated 426-nm light is generated by frequency doubling of a modulated 852-nm distributed Bragg reflector diode laser. Absorbances of are measured with second-harmonic WMS with a signal-to-noise ratio of 3:1 in a 3-Hz measurement bandwidth. The feasibility of simultaneous line-of-sight absorption and spatially resolved laser-induced-fluorescence detection with a single excitation beam is also demonstrated. This near-UV source is suitable for microgravity drop-tower experiments and other applications in which compact, rugged, energy-efficient instrumentation is required.
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