The TCSPC Oscilloscope

If a TCSPC module is operated at a eount rate of 10 to 10 photons per seeond a reasonably aecurate waveform is reeorded within less than 100 ms. Advaneed TCSPC modules can therefore be used as optieal oseilloseopes. A repetitive measurement eyele is performed in short intervals and the reeorded photon distribution versus time is displayed. Even with a low-eost PMT module, e.g. the Hamamatsu H5783, an IRF width of about 180 ps is aehieved. This eorresponds to a signal bandwidth of almost 2 GHz. The time ehannel width ean be made as short as a picoseeond, which results in an equivalent sample rate of 1,000 GS/s. 

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. 

In practice a stack of filters in front of the PMT is used for convenient operation under normal daylight eonditions. A narrow-band interference filter with a transmission centred at the wavelength of the detected signal can be added to reduee the daylight sensitivity. 

Convenient detectors for oscilloscope applieation are the Hamamatsu H5783 or H5773 modules, or deteetor heads based on these modules. The modules have a 

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. 

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