Multidimensional TCSPC Techniques

Compared with the very limited capacity of the more or less discrete control electronics of classic TCSPC systems, the use of FPGAs led to a breakthrough in functionality. Advanced TCSPC devices use a multidimensional histogramming process. They record the photon density not only as a function of the time in the signal period, but also of other parameters, such as wavelength, spatial coordinates, location within a scanning area, the time from the start of the experiment, or other externally measured variables. It is actually the multidimensionality and flexibility in the data acquisition process that makes new TCSPC techniques really advanced . 

The general architecture of a TCSPC device with multidimensional data acquisition is shown in Fig. 3.1. 

The additional address bits provided by the channel register and the sequencer are often termed routing bits , and the technique is termed routing . Depending on the information fed into the channel input, a number of novel signal acquisition principles are available  

The most frequently used multidimensional recording modes and their combinations are described in the next paragraphs. 

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A variation of the TCSPC technique does not build up photon distributions but stores information about each individual photon. This is called time tag , time stamp , list , or FIFO mode. The memory is configured as a FIFO buffer. For each photon, this method stores the time in the signal period ( micro time ), the time from the start of the experiment ( macro time ), and the data word at the channel input. During the measurement, the FIFO is continuously read, and the photon data are transferred into the main memory or to the hard disc of a computer. Advanced TCSPC devices often can be configured either to build up a multidimensional photon distribution or to store the individual photons. The FIFO mode is described in Sect. 3.6, page 43. 

This is exactly what advanced multidimensional TCSPC is capable of. The scanning technique of advaneed TCSPC (see page 37) therefore almost perfectly fits the laser seanning mieroseope. 

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