Abstract

This paper describes a time-correlated single photon counting (TCSPC) technique for picosecond resolution multi-wavelength lifetime imaging in two-photon or confocal laser scanning microscopes and other scanning systems. The technique uses a four-dimensional histogramming process that records the photon density versus the time within the fluorescence decay function and the x-y coordinates of the scanning area in several detector channels simultaneously. Due to the large number of time channels the components of multi-exponential decay functions can be resolved down to 30 ps. A single TCSPC imaging channel works with a high detection efficiency up to a photon count rate of about 5^.10⁶ s^-1. Although this is much more than typically obtained from biological specimens in two-photon laser scanning microscopes higher photon rates are available from macroscopic samples or in diffuse optical tomography experiments. Our imaging system can therefore be extended to four fully parallel TCSPC channels. The four-channel system can be operated at a total count rate of 20^.10⁶ s^-1.

© 2004 Optical Society of America