CCD detection and Modulation: Can it be done?

[Roy Tucker]

Posted to CCD-world:
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At 11:03 AM 2/2/98, you wrote:
>Posted to CCD-world:
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>Hello All:
>
>My company uses CCD detectors as integrating detectors for low light
>level spectroscopy.  I have an application in which I need to discriminate
>between my analytical signal and ambient light.  If I were using 
>a photomultiplier tube, the solution would be simple.  I would chop
>my excitation light source (which generates my analytical signal when
>it interacts with my sample) at some set frequency (chosen not to
>have interference from common frequencies (e.g. 60 Hz)) and then I
>would look at the response from the PMT that was modulated at that
>frequency.  The ambient light would be DC and would then be descriminated.
>
>I cannot think of ANY way to achieve this type of simple modulation with
>an INTEGRATING detector like a CCD.  Does anyone out there have any 
>suggestions?
>
>Thanks for any help.
>
>Scott Sutherland
>Senior Scientist
>GAMMA-METRICS
>
>BTW, the one of our major applications requires that the CCD signal be
>read out every 10 msec, so the modulation solution would need to be
>able to discriminate between CW and modulated light in a 10 msec window.
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owner-CCD-world at cfht.hawaii.edu.
>
>
Hi Scott,
     How about arranging a chopping mechanism that chops between two
spectra on the surface of the CCD, one is signal plus ambient and the other
is only ambient. Subtraction would give you just the signal. Better yet
would be a four spectrum solution so you're not throwing away half the
signal. Possibly this has occurred to you and it was not feasible for some
reason?
							- Roy Tucker


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For information about CCD-world, send email to owner-CCD-world at cfht.hawaii.edu.