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Faq 005
Dear Photomultiplier Doctor,
The direct o/p of my 9558QB photomultiplier, without amplification, is an ac component with approx a 200mV dc offset. Is this right? It means I cannot use a dc coupled amp as it saturates.
Using a slower amp, measurements can be done with typical PL measurements giving a few mV of signal to a lock in using an amp with 103 amplification (this amp must be ac coupled).
It sounds like you have a light leak. You can check by doing any of the following and checking the
output again:
- Throw a cloak over the photomultiplier.
- Switch off the lights.
- Wait until dark.
- Check you are not operating the photomultiplier above the recommended voltage as given on the test ticket.
I have come across this before because it is actually quite difficult to make a light tight enclosure. If this is not the problem then maybe the photomultiplier has developed an internal leak path.
If you can't resolve the problem let me know and we can arrange for you to send the photomultiplier back to us for retest.
Regards,
Photomultiplier Doctor.