Rapid measurement of fluorescence lifetimes using SiPM detection and waveform sampling

In this work we demonstrate, for the first time, the feasibility of making rapid fluorescence lifetime measurements with analog silicon photomultipliers (SiPMs) and waveform sampling techniques. Fluorophore excitation was provided by means of a low-power fiber-coupled pulsed laser diode operating at 405nm, whose beam had been expanded to a diameter of 2mm before impinging upon the sample. A portion of the sample's isotropic fluorescent emission was collected orthogonal to the incident excitation beam via an analog SiPM and analyzed by waveform sampling at 2.5 GS/s. Fluorophores for system evaluation were selected such that their fluorescence lifetimes differed significantly from one another but their excitation and emission wavelength's maxima did not, and included Coumarin 6, Coumarin 314, and Coumarin 343, each dissolved in ethanol. Measurements were made of a non-fluorescent, isotropically-scattering specimen to derive the system's response function. Single exponential fitting of the convolution of the system's response function with each dye's intrinsic fluorescence intensity function yielded fluorescence lifetimes in close agreement to those derived from measurements made on a commercial system.