In 1984 Desmond O'Connor and David Phillips published their
comprehensive book "Time-correlated Single Photon Counting". At that
time time-correlated s- gle photon counting, or TCSPC, was used
primarily to record fluorescence decay functions of dye solutions in
cuvettes. From the beginning, TCSPC was an am- ingly sensitive and
accurate technique with excellent time-resolution. However, acquisition
times were relatively slow due to the low repetition rate of the light
sources and the limited speed of the electronics of the 70s and early
80s. Moreover, TCSPC was intrinsically one-dimensional, i.e. limited to
the recording of the wa- form of a periodic light signal. Even with
these limitations, it was a wonderful te- nique. More than 20 years have
elapsed, and electronics and laser techniques have made impressive
progress. The number of transistors on a single chip has approximately
doubled every 18 months, resulting in a more than 1,000-fold increase in
compl- ity and speed. The repetition rate and power of pulsed light
sources have increased by about the same factor.