Development of a Filtering Technique for Planar Laser-Induced Fluorescence of the CH Radical with Diagonal Excitation/Observation

A computational design tool has been developed and applied to a new fluorescence filtering scheme for the CH A²Δ_↔X²π transition, which uses diagonal excitation and observation to provide the highest possible excitation and emission strengths in systems with high quenching. A holographic notch filter is proposed to reject elastic scatter while a 10 nm bandpass filter isolates CH fluorescence from other emissions. The computer simulation of the fluorescence process was employed to determine the combination of filters and excitation wavelengths that provided the highest fluorescence signal. Optimum filter configurations were determined for a spectrum of pressures, temperatures, and quenching environments. The analysis shows that this technique is best suited to high-pressure environments where saturation is not possible, and the signal strength of this diagonal excitation/observation technique in such environments is at least an order of magnitude greater than that for previous off-diagonal techniques.