Fluorescence lifetime measurements are widely used in exploring various biological environments, revealing changes in pH, temperature, and viscosity among other parameters [1]. Measurements are typically performed with time-correlated single photon counting (TCSPC) methods, which are limited to 100’s of picoseconds lifetime resolution due to limitations of electrical hardware [2]. Recently, Fluorescence lifetime Hong-Ou-Mandel sensing (FLHOM) method [2], where temporal resolution is limited by optical properties of light, overcomes the limitations of standard technique. Here, we introduce a low-cost version of the FLHOM method, by replacing a coherent reference source with a thermal source.
We used Allura Red fluorescent dye, with a nominal lifetime of ~1.6 ps [2], as a reference source to probe the lifetime of a 4-DASPI dye in a Mach-Zehnder interferometer set up. Secondly, we deconvolved the measured second-order correlation function and recovered fluorescence lifetime of 5.6 ps, in agreement with previous findings [2]. We measured a reduced interference visibility around 6.5% due to intrinsically bunched nature of thermal light. In conclusion, integrating fluorescent dye as a reference thermal source reduces the complexity and cost of the experimental system. Despite marginal reduction in achievable lifetime resolution, the method opens opportunities to measure ultrashort fluorescence lifetime.