The laser pulses will be given entire histogram(i. e. the total time scale) or will it be given at the initial time, on the X-Axis at time x nanosecond the fluorescence is about 80% compare to the initial counts intensity, here it is not clear that the 80% counts and then single photon counting ?
Dear Dr Pendyala,
You can read more about TCSPC in the book that I link you below, but I can give you a general description about the technique.
TCSPC actually measures the time-delay between two signals, the signal of photoluminescence coming from the sample and the signal of an electrical pulse generator which triggers the laser (or LED) source. After being triggered by the electrical pulse generator, the laser (LED) produces pulsed light with the same time profile as the electrical pulse. The same electrical pulse was sent simultaneously both to the laser (LED) and to the detector and that time was set as zero. So, the detector compares the time-delay between the two signals, the signal which triggered the laser and the photoluminesce from the sample, and then it puts a count at the specific point which corresponds to the specific time delay of the photon relative to the electrical pulse. The above mentioned procedure is repeated many times and so more photons are added on the histogram.
The term single photon counting comes from the fact that in the time interval between two consecutive excitations (between two consecutive pulses) only one photon, emitted by the sample, can be detected. When this photon is detected it is put on the histogram and is added to the previous photons which had the same time-delay with it. That is why in every cycle the counts on the histogram grow.
Of course, as you will see in the book, the technique is more complicated than I described you as there are many electronic elements involved and some key steps such as how exactly is the time-delay between the two signals recorded.
I hope this answer to be helpfull to you.
http://www.springer.com/us/book/9783319149288
Dear Dr Kapusta,
You are right, my answer was very general but I could not write too much on the subject and get into a lot of details as I thought that the question needed just a general view of the technique. I thank you for your suggestion and I hope that this will help Dr Pendyala.
Best regards, Nikos
Dear Dr. Nikolaos and Dr. Kapusta,
Thank you so much for your discussion.
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