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Faq 002

Dear Photomultiplier Doctor,

Can you please resolve a dispute I am having with a physicist at work. The problem concerned having too much signal from the photomultiplier, which I remedied by attenuating the light input with a neutral density filter. He said that I should turn the gain of the photomultiplier down rather than attenuate the light input but I think the two options should produce the same result.

Yours sincerely,

S C Jamieson

Dear Mr Jamieson,

The physicist is right - don't attenuate the light. The information in the light signal is statistical in nature and by attenuating the signal you throw away information. This is always true, regardless of the statistics that govern the behaviour of the light source, and has the effect of increasing the noise in the signal. For light sources that obey Poisson statistics, the signal-to-noise is proportional to the square root of the number of photoelectrons detected so do what ever you can to detect more light.

Whatever you do, never throw away light.

Regards,

Photomultiplier Doctor.