Fluorescence Lifetime Spectrometer

FluoTime 200

FluoTime 200 - example of a very short IRF 

The FluoTime 200 spectrometer was equipped with a Hamamatsu R3809U-50 MCP photomultiplier tube, amplified with PAM102-M preamplifier. TCSPC data was acquired with the PicoHarp 300, operated at maximum temporal resolution of 4 ps per channel.

The excitation source was a Spectra-Physics Millenia Pro pumped Tsunami Ti:Sapph laser oscillating at 80 MHz. The pulse repetition rate was reduced to 8 MHz and frequency doubled, yielding optical pulses with a duration of less than 2 ps (FWHM) at λ = 400 nm. The remaining radiation with fundamental frequency after the doubling was used to pick up the sync signal with a TDA 200 fast photodiode.

The picture below shows the resulting 32 ps FWHM instrument response function. The weak satellite peak is a typical afterpulsing behaviour of the MCP-PMT detector.

The IRF duration is determined mainly by the transit time spread of the detector. This IRF was measured in a standard way, i.e. using a 10 mm path length cuvette with a scattering solution. It should be noted, that it takes approximately 30 ps for the light pulse to travel through this cuvette, and the pulse remains in focus of the detection optics at least for 10 ps. The 32 ps result proves that the broadening caused by the PicoHarp 300 is negligible.