Optical calibration of the picosecond time scale and correlated backgroundelimination in fluorescence dynamics 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 on 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 i s proposed for eliminating the time-correlated background appearing mainly due to Raman scattering and trace impurities in solvents, which is a seriou s impediment in TCSPC measurements and analysis of excited state decay in t he picosecond time scale. The problem of the correlated background eliminat ion is particularly important for samples of the excited state decay times of single picoseconds, which usually show very weak luminescence.