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High-resolution absorption measurements of CO 2 were made in a heated static cell and in the combustion region above a flat-flame burner for the development of an in situ CO 2 combustion diagnostic based on a distributed-feedback diode laser operating near 2.0 m. Calculated absorption spectra of hightemperature H 2 O and CO 2 were used to find candidate transitions for CO 2 detection, and the R͑50͒ transition at 1.997 m ͑the 1 ϩ 2 2 ϩ 3 band͒ was selected on the basis of its line strength and its isolation from interfering high-temperature water absorption. Measurements of spectroscopic parameters such as the line strength, the self-broadening coefficient, and the line position were made for the R͑50͒ transition, and an improved value for the line strength is reported. The combustion-product populations of CO 2 in the combustion region above a flat-flame burner were determined in situ to verify the measured spectroscopic parameters and to demonstrate the feasibility of the diode-laser sensor.

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A high-luminosity-light-collection system for highly spatial detection of chemiluminescence of radical species in flames has been developed. The system, multi-colour integrated Cassegrain receiving optics (MICRO) is based upon a Cassegrain-type configuration, which implies that it employs only reflective components (in combination with an optical fibre for light collection). It provides therefore spherical- and chromatic-aberration-free detection, which is of importance for high-spatial-resolution measurements and for the simultaneous monitoring of signals in different wavelength regions from a given spatial volume. The effective light-collection volume has been estimated to be only 1.6 mm × 0.2 mm × 0.2 mm by ray-tracing techniques, which is more than three orders of magnitude smaller than that provided by a corresponding simple single-lens system and comparable to that of laser-based techniques, e.g. Doppler anemometry. The system is also easily aligned since the active probe volume can be visualized by sending in visible light through the system in the reverse direction. In order to demonstrate the performance of the system, OH-radical chemiluminescence in a Bunsen flame was monitored using MICRO and compared with the ion-current signal from a Langmuir probe with a minute sensor tip. A good correlation between the fluctuations in the two signals could be obtained, proving the high spatial and temporal resolution of the MICRO system.

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