Abstract

A method for laser-induced fluorescence (LIF) imaging of formaldehyde (${\mathrm{CH}}_2\mathrm{O}$) that discriminates against the interfering signal from polycyclic aromatic hydrocarbons (PAHs) is presented. This technique uses an interference filter with 11 transmission bands that closely match the most prominent fluorescence features of ${\mathrm{CH}}_2\mathrm{O}$ upon excitation at 355 nm. The signal increases by a factor of 12 with the multi-band filter compared to a single-band filter. Slight angle-tuning of the filter shifts the transmission maxima to the minima in between the ${\mathrm{CH}}_2\mathrm{O}\text{-}\mathrm{LIF}$ features. The pixel-by-pixel difference between the images collected at the two filter angles thus provides ${\mathrm{CH}}_2\mathrm{O}$ images free of PAH interference, providing the capability for selective single-pulse ${\mathrm{CH}}_2\mathrm{O}\text{-}\mathrm{LIF}$ imaging in engine combustion even under fuel-rich conditions.

© 2014 Optical Society of America

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