*J. Grace, S. Edlou, J. Foss, C. Hodgson, J-P Rheault, J. Rosvold, K Sieber, S. Walters, IDEX Health and Science, LLC, West Henrietta, NY
In fluorescence microscopy and related applications, fluorescence from optical elements in the system can be a limiting factor in achieving low background levels. Such “autofluorescence” is considerably weaker than the fluorescence produced by the organic dyes used in fluorescence-based analytical techniques. While spectrally detailed information of autofluorescence is desirable, such information comes at a cost of sensitivity. We present straightforward approach to making sensitive fluorescence measurements using a simple chopped laser and lock-in detection scheme. By using high-quality optical filters in the excitation and detection paths, the trade-off between spectral information and ultimate sensitivity is controlled by the choice of filter edge location and bandwidth. An initial implementation of this approach, using a 405 nm diode laser as an excitation source, achieves a sensitivity of ~1 pW optical power of detected fluorescence over a bandwidth of ~125 nm centered at 505 nm. Data from measurements on glass substrates will be presented, and challenges for evaluating autofluorescence from coatings on glass will be discussed.