Evaluation of single-photon-counting measurements of excited-state lifetimes.

An extremely short instrumental response function for a single-photon-counting system has been obtained by using a low-jitter photomultiplier tube, fast amplification of the single photoelectron pulse from this photomultiplier, a constant fraction discriminator with a wide bandwidth input, and a stable reference timing signal. This synchronously mode-locked laser system has been shown to be capable of measuring the fluorescence lifetimes of compounds from 66 psec to 4.5 nsec. The estimated error in these determinations is 6% or 10 psec, whichever is greater. This apparatus has proved itself to be superior to the previously used nitrogen flashlamp apparatus for the determination of subnanosecond lifetimes. The validity of using deconvolution to determine lifetimes shorter than the instrumental response function has been verified.