Detector
TM-5 utilizes PTI patented stroboscopic detection system. It comprises a photomultiplier (PMT) and controlling electronics. The PMT is pulsed at the rep rate and in sync with the pulsed LED source. Software-controlled electronics provides a very precise timing between the LED flash and the pulse controlling the PMT gain and the temporal window.
In a conventional pmt detector, the PMT dynodes are wired with a bank of resistors that determine the voltage distribution between the dynodes. In the stroboscopic detection each resistor in the dynode chain is replaced by a delay line, the length of which is matched to the time it takes for electrons to travel between each of the dynode pairs (see Fig. 1). The pulse synchronized with the LED flash is then injected into the dynode chain D1. This pulse causes a transient potential difference between each dynode as it travels down the delay line connecting each dynode. The net result is that the packet of electrons started by a photoelectron ejected from the photocathode C is selectively amplified as it passes down the dynode chain. Of significance to the stroboscopic technique is that the PMT is sensitive to photons arriving at the photocathode C only when the high voltage pulse HV is between the photocathode C and the first dynode D1. Thus a narrow integration window of amplification is formed, which can be moved across the fluorescence decay and the fluorescence intensity at different delay times is recorded (Fig. 2).
Fig. 1. Stroboscopic detector diagram
Fig. 2. The integration window will record the intensity of the decay between time ti-Δt and ti+Δt. The window is scanned in time to record the intensity of the decay
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