Optical calibration of the picosecond time scale and correlated background elimination in fluorescence dynamic measurements by time-correlated photon counting.

A simple, feasible and precise method of calibration of the time scale of a TCSPC laser spectrometer is devised, based in the insertion of an optical delay into one of the start/top channels. The delay can vary from a fews ps to about 1 ns depending on the geometry and refractive index of the medium used, and can be determined with an accuracy better than 1%. A procedure is proposed for eliminating the time-correlated background appearing mainly due to Raman scattering and trace impurities in solvents, which is a serious impediment in TCSPC measurements an analysis of excited state decay in the picosecond time scale. The problem of the correlated background elimination is particulary important for sample of the excited state decay time of single picoseconds, which usually show very weak liminescence.