TCSPC oscilloscope

As an example. Fig. 1.4 shows the single-electron response measured with a high-speed oscilloscope and the transit-time distribution for a Hamamatsu R3809U MCP PMT measured by TCSPC. 

The total eost of a TCSPC oseilloseope system is no higher than that of an optical oscilloscope consisting of a fast photodiode and a fast oscilloscope. However, the sensitivity is many orders of magnitude greater. Moreover, the detection area of a PMT is much larger than that of an ultrafast photodiode, so alignment is no longer an issue. 

Fig. 5.144 Fluorescence signal recorded in an TCSPC oscilloscope setup. One channel of a Becker Hickl SPC-144, detector count rate 6 MHz, recorded count rate 4 MHz, 1,024 time bins per curve, acquisition time 100 ms per curve. To reproduce the visual impression, two successive traces were overlaid...

Recently fast and relatively inexpensive SPAD modules have become available [245]. The detectors have an active area of 50 pm diameter and are overload-proof The IRF width is about 40 ps, resulting in an equivalent signal bandwidth of about 9 GHz. Although the small active area can cause some alignment problems, these detectors are excellently suitable for TCSPC oscilloscopes. 

A TCSPC oscilloscope mode is implemented in most advanced TCSPC modules. The mode has become an indispensable tool for a large number of technical jobs. Alignment and optimisation of optical systems often requires not only maximising the efficiency but also localising and removing optical reflections, leakage of excitation light, or pulse dispersion. 

The oscilloscope mode is also used to optimise detectors and the driving conditions of picosecond diode lasers. Another potential application is beam monitoring in synchrotrons. Furthermore, the oscilloscope mode is a convenient way to optimise TCSPC system parameters, such as signal delay, CFD zero cross and threshold, and TAC parameters. 

The SER of a PMT can also be recorded by splitting the signal and triggering the oscilloscope externally via a CFD. It is then possible to use a sampling oscilloscope or a fast boxcar device to record the pulse shape. There is, however, no reason why a normal TCSPC user should take such effort to record an SER pulse shape. 

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