Discussion:
overrun detector readout noise by adding offset background light for low light signals
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l***@gmail.com
2017-05-11 20:11:07 UTC
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Dear all,

It's a practical as well as a theoretical question.
There are some conditions where light signal that we need to detect is below the detector noise. I was guessing if it is possible in some conditions, to add a controlled constant background light (which would act as an offset), so that the total signal gets higher than the detector threshold detection limit.
Linked to this question, is it possible that a photodetector (including the sensor and the attached electronics)can't detect, let's say 0.1 mWatt light out of the dark (because of it's dark current or other kind of noise), but can resolve between 1 mW and 1.1 mW.
Of course I'm aware that background light would carry an associated photon shot noise, and the trick would be to add a minimum amount of background just to get above the detector noise level.

Thanks,

Eric
Phil Hobbs
2017-05-12 13:51:57 UTC
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Post by l***@gmail.com
Dear all,
It's a practical as well as a theoretical question. There are some
conditions where light signal that we need to detect is below the
detector noise. I was guessing if it is possible in some conditions,
to add a controlled constant background light (which would act as an
offset), so that the total signal gets higher than the detector
threshold detection limit. Linked to this question, is it possible
that a photodetector (including the sensor and the attached
electronics)can't detect, let's say 0.1 mWatt light out of the dark
(because of it's dark current or other kind of noise), but can
resolve between 1 mW and 1.1 mW. Of course I'm aware that background
light would carry an associated photon shot noise, and the trick
would be to add a minimum amount of background just to get above the
detector noise level.
Thanks,
Eric
Adding more incoherent light just makes the problem worse--the signal to
noise ratio decreases steadily as you add more. Coherent detection, on
the other hand, can get you sensitivity equivalent to an ideal photon
counting system (the shot noise of the signal beam dominates
everything). Of course you have to be detecting laser light from a
small (i.e. unresolved) region of space for that to work well.

I've built quite a few coherent detection instruments--in the right
application they're like magic.

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
g***@gmail.com
2017-05-12 17:20:46 UTC
Permalink
Post by l***@gmail.com
Dear all,
It's a practical as well as a theoretical question.
There are some conditions where light signal that we need to detect is below the detector noise. I was guessing if it is possible in some conditions, to add a controlled constant background light (which would act as an offset), so that the total signal gets higher than the detector threshold detection limit.
Linked to this question, is it possible that a photodetector (including the sensor and the attached electronics)can't detect, let's say 0.1 mWatt light out of the dark (because of it's dark current or other kind of noise), but can resolve between 1 mW and 1.1 mW.
Of course I'm aware that background light would carry an associated photon shot noise, and the trick would be to add a minimum amount of background just to get above the detector noise level.
Thanks,
Eric
Isn't the detector noise going to be there regardless of the light level?
If the signal is smaller than the noise you have to average some how.
(More details of your system would help.)
Can you use a different detector 100 uW sound like a lot of signal.
(unless it's some room temperature FIR detector.)

George h.
B0il jims
2017-05-16 11:22:32 UTC
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