HOW MANY PHOTONS ARE NECESSARY FOR FLUORESCENCE-LIFETIME MEASUREMENTS

On planning time-correlated single photon counting experiments for fluorescence-lifetime measurements with minute samples, the question of ultimate sensitivity arises. To answer this question, we will find out how many detected photons one needs to achieve a certain accuracy in the lifetime estimate. Using-least-squares or maximum-likelihood procedures and the multinomial distribution, the accuracy of the lifetime estimation can be expressed explicitly as a function of the signal strength. This allows one to determine the required number of detected photons.