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 5×10<sup>-5</sup> are measured with second-harmonic (2f) 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.
© 1999 Optical Society of America
(120.1740) Instrumentation, measurement, and metrology : Combustion diagnostics
(120.1880) Instrumentation, measurement, and metrology : Detection
(140.2020) Lasers and laser optics : Diode lasers
(190.2620) Nonlinear optics : Harmonic generation and mixing
(300.6380) Spectroscopy : Spectroscopy, modulation
Kristen A. Peterson and Daniel B. Oh, "High-sensitivity detection of CH radicals in flames by use of a diode-laser-based near-ultraviolet light source," Opt. Lett. 24, 667-669 (1999)