Hi,
I saw this article today, showing a method for increasing the bandwidth while maintaining high sensitivity in a SPAD (single pulse avalanche diode). The numbers are 5GHz bandwidth, 200ps bias signal used for gating, and 60% light detection efficiency, approaching the 70% theoretical maximum efficiency for the SPAD used:
cheers, Jamie
Another take on that:
SPADs are pathetic except in terms of bandwidth. Their false count rate is so horrible that you have them turned completely off almost all the time to avoid being blown out of the water by afterpulses from the false counts.
You can get the same sorts of efficiencies by coupling light into the glass envelope of a PMT above the critical angle, so that it has to rattle around inside the glass and photocathode till it gets absorbed. Plus the false count rate is many orders of magnitude less.
It's a bit slower, about 1 ns for a negative electron-affinity photocathode.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
The article was very short of details. But I think it said something that was already known, (I've only read like 1 or 2 spad articles.) As you reduce the bias level the after pulses tend to go down exponentially. (The signal level is also non-linear with the bias level, but maybe less so??) Anyway it can be a win to run them at lower bias levels. Spad's aren't all that bad, anything that can count single photons is pretty cool.
George H.
Jamie, you might like this review article in RSI.
For some reason it's free! (I've downloaded, but haven't read it.)
George H.
Thanks, looks like a good article!
cheers, Jamie
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