Hi,

In a most TCSPC setups, you can introduce an arbitrary delay between the start of the TCSPC time axis and the laser pulse (which defines the beginning of the decay). Typically you want to capture the whole rising edge of the TCSPC histogram (e.g. to be able to perform re-convolution fit), so you position it at a small positive time.

Radek

Radek Machan Thank you so much Sir. Can we start it at zero, I mean without any delay between the laser pulse and TCSPC time axis? If yes, then what about the re-convolution fit? I am sorry I am the beginner so I am confirming that the delay is better or not? thanks

Hi, there's no benefit in placing the "beginning" of the decay to 0 - it is just a trivial offset in the fit. Secondly, the "beginning " of the decay is not an obvious thing because in the actual TCSPC data the decay is convolved with IRF. How would you define what is the "beginning" of the decay? The maximum of the curve? If you choose the maximum of the curve, then the rising edge will appear at the end of the time window, making reconvolution fitting cumbersome (IRF being split between the beginning and the end of the time axis). Thirdly, there's a practical aspect to it - in older setups (and I don't mean necessarily very old ones) the only way how to tune the synchronisation of the laser pulses with the TCSPC time-base is by the length of the cables (how long the electrical pulse needs to travel the length of the cable). The cables you have available limit your freedom in setting the position of the rising edge of the TCSPC curve.

Radek Machan , I got it, Thank you so much Sir.

Regards

Qaseem Khan

One more point I forget to mention - the part before the rising edge is usually used to determine the baseline of the curve used in the fits