Phase-locked detection of fluorescence lifetime

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Abstract
A newly developed category of signal processing scheme for the detection of fluorescence lifetime is discussed, with application to a number of inexpensive, compact, and reliable fluorescence lifetime‐based fiber optic sensors. With phase‐sensitive detectors being used to achieve a high noise‐suppression ability, the schemes discussed here include some of the features of existing phase and modulation techniques for lifetime measurement. However, they differ from them in several aspects, especially in that they operate in a way rather similar to that of a phase‐locked loop. Based on such schemes, the measured lifetime is converted to a repetitive signal whose period is directly proportional to it, and thus a high measurement resolution can be achieved. Such schemes can be operated over a wide consecutive measurement range of fluorescence lifetime, and they are particularly useful for temperature sensor applications using long lifetime (≳1 μs) fluorescent media. Illustrations of the applications of these schemes in lifetime‐based fiber optic thermometers are presented showing their promising potential for both biomedical and industrial uses.