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A time-gated fluorescence detector using a tuning fork chopper

“…Afterpulse effects can be caused by many sources, such as UV-induced phosphorescence, microdischarge events produced during a high-gain operation, electron-induced positive ions hitting the photocathode or the dynodes, etc. [18][19][20][21]. The afterpulse effects can create particular problems in detecting a weak luminescence signal after a strong excitation pulse: in our previous detection systems, the afterpulse signal was of a high enough magnitude with the GPMT operated at a modest gain; the full advantage of the high gain of this device could not be fully realized.…”

“…Both these detectors however, used electronically gateable relatively expensive gated photomultiplier tubes (GPMTs). All photomultiplier detection systems exhibit this is an "afterpulse" that stem from the memory of the photocathode after it has been exposed to a strong short light pulse, even though the tube was not gated on [18][19][20][21]. The result is an exponentially decaying weak signal that can last milliseconds after the photomultiplier tube (PMT) is exposed to an intense short optical pulse, even though it was gated off during the excitation period.…”