Picosecond Timing with Microchannel Plates, Microchannel Plate PMTs, and Channeltrons

Microchannel plates and channeltrons are often used for single-ion counting and timing, while microchannel plate photomultiplier tubes find application in single-photon counting and timing. The amplification mechanisms in these detectors are similar to those in a conventional photomultiplier tube, except that the discrete dynodes of the normal PMT are replaced by a continuous dynode formed by a resistive glass tube. The intrinsic contribution to timing jitter in these detectors comes from variations in electron transit times through the device, and fluctuations in secondary-electron yields throughout the glass channel. The microchannel plate structure offers much smaller transit times and proportionately less transit time spread compared to a conventional photomultiplier tube. Consequently, these faster detectors also deliver better time resolution than a conventional PMT.

Microchannel plates, microchannel plate PMTs, and channeltrons produce very small output pulses with ultra-short pulse widths. Rise times are typically 150 to 700 ps, and the pulse widths (FWHM) are equally brief. Therefore, an amplifier with an extremely fast rise time is needed between the detector and the timing discriminator. The Preamplifier section of this catalog should be consulted for the proper choice of amplification. Because of its wide bandwidth, the preamplifier contributes electronic noise to the signal, and this adds to the timing jitter via the mechanism described in Equation (10). Best timing resolution is usually achieved when the amplifier rise time is comparable to the detector rise time.

For single-ion and single-photon timing, the amplitude fluctuations at the detector output are extreme, and one would expect that this situation demands a constant-fraction discriminator to minimize walk. Unfortunately, conventional constant-fraction discriminators do not have adequate bandwidth to properly process signals with rise times as short as 150 ps and pulse widths of the order of 400 ps. The Model 9307 pico-TIMING Discriminator was developed to solve this problem. It accommodates the ultra-short pulse widths and incorporates a special circuit to eliminate walk (time slewing) over a wide range of pulse amplitudes. Pairing the Model 9306 1-GHz Preamplifier with the Model 9307 pico-TIMING Discriminator is the best solution for achieving optimum time resolution with microchannel plates, channeltrons, and microchannel plate PMTs. Actual performance is documented in the Model 9307 data sheet. The 9327 is a more convenient solution that combines the 9306 and 9307 functions in one compact preamplifier package.