Development of a Multi-Color light collection probe with high spatial resolution (1st Report, Evaluation of spatial resolution by Ray-Tracing Method)

Spot monitoring of radical chemiluminescence is especially useful for flame diagnostics, if the measuring control volume size can be clearly defined. However, a typical light collection system consisting of a spherical lens and a pinhole suffers from its wide and long control volume, as well as its significant chromatic aberration between UV and visible ranges in simultaneous multi-color measurement. In some cases, researchers were obliged to insert a control-volume limiting device into the flame for observing the local emission intensities of radical chemiluminescence. To resolve these problems, we have developed a light collection probe of Cassegrain type, which consists of a set of concave and convex mirrors combined with an optical fiber cable, and is free from both chromatic and spherical aberrations, which was named Multi-color Integrated Cassegrain Receiving Optics (MICRO). The spatial resolution was analyzed by the ray-tracing method, and the effective control volume size was estimated as 1.6 mm-long and 200 μn diameter, which is as small as that of LDA or PDA.