Hello,
We use a femto second laser and a Becker and Heckl TCSPC card to conduct fluorescence lifetime experiments (TCSPC). We use nile red in an oil to perform bulk experiments.
Things were fine until recently we noticed that the intensity decay curves always show two peaks. It looks as if the sample has been excited twice within the lifetime of the dye and their decay curves overlap each other. We have tried with samples in petris dish, in a curvette, on a slide but still the same problem. We have removed all the optics and just had the sample directly in front of the laser and still have the problems.
May I ask if anyone here has experience about this issues and how this may be solved? Thanks very much in advance.
Hi Philippe, We did. At low concentration, same problem. In fact, the problem becomes more obvious. We also have tried a different dye in toluene. Same thing...
I am not familiar with this particular setup but can you show us the decay? How does the instrument response function (IRF) look like? In TCSPC based system sometimes we notice strong after-pulse. An IRF will give an idea of whether the problem is in the system or the sample. What is the time gap between the two "peaks"? What is the lifetime of the dye and what is the repetition rate of the laser? These informations might help us understand the problem.
Double peaks can also have instrumental reasons. If mode locked fs lasers are used a double peak in the decay curve can indicate laser instability (mode locking is lost for a short period). The very first thing to check is the min/max value of the sync rate (load, block info, in the end of the info there is a line with the info).
Janet S. S. Wong , if I remember correctly you had a relatively old Tsunami with 90 MHz, right?
Dear Sir
Janet S. S. Wong
We are also dealing with a similar problem Duel peak decay curve as well as an unusual broadening of the peak. If you have got the solution please kindly share it with us. We will be very grateful to you. The problem also occurs in the peak of the Instrument Response Function (IRF).
Piyush Singh, I have no experience with your system. Tuning the CFD thresholds for the detector might help.
I'd recommend to contact the manufacturer.
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