The LED pulsing tests were used to determine the width of the shortest pulse that can be produced by an LED. An Avtech pulse generator was used to send a voltage pulse through an attenuator to pulse the LED.
A photomultiplier tube detected the emitted light and the corresponding pulse width was measured. Data was taken for 10, 50, 100, 500, 1000 photoelectron signals (for single photoelectron studies see SPE studies) with the PMT set at 1900V using ~3ns voltage pulse. The data shows that the LED can generate a pulse of at least 6ns.
A sample of the voltage pulse from the pulse generator was view on the oscilloscope for the pulse used to produce the 10, 50, 100 photoelectron signals and for the pulse used to produce the 500 and 1000 photoelectron signals.
The signals plotted below, show that a small change in amplitude produces a substantial change in the number of photoelectrons.
The conclusion is that an LED can produce a pulse of a least 6ns and still yield up to a several hundred photoelectron signal. The pulse width seems to increase slightly as the number of photoelectrons exceeds ~500. However, detailed studies of this effect were not performed and the results should be considered inconclusive for the 1000-photoelectron signals.