Technology

Instrument design

Fluorescence excitation is done by using modern and compact pulsed lasers. The duration of the laser pulses varies between 1 and 3 nanoseconds according to the type of pump laser. Due to the high laser pulse energy of several microjoule per pulse a very high detection sensitivity of weak fluorescence intensities is achieved. The short duration of the laser pulses is the basis for the possible resolution of fluorescence lifetimes on the low nanosecond time scale. The special concept of the electronical signal recognition (single laser pulse digitizing) enables the measurement of fluorescence lifetimes within an exceptional broad range: between 1 nanosecond and 10 milliseconds.

The pump laser emits short pulses at 337 nm with a repetition rate between 10 and 50 Hertz. These pulses pump a second laser - a dye laser. The second laser provides excitation wavelengths up to 1000 nm. Changing the excitation wavelength is easily done by exchanging the dye laser modules (picture to the right). A list with currently available laser modules can be downloaded here.

The excitation laser pulses are focused into an optical fibre. The fibre delivers the excitation light to the sample. There fluorescence labels like fluorescein, rhodamine, cynanine or native fluorophores like NADH, flavines, porphyrines are excited and start to fluoresce. The fluorescence light is collected by the same or another optical fibre and directed back to the detector.

The signal is detected by a photomultiplier tube after spectral filtering with an appropriate bandpass filter. The spectral filtering is done either using a fixed wavelength filter or an acousto-optic tuneable filter (AOTF) at variable wavelengths. Signal recognition is done with the method of "single laser pulse digitizing".