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Hi Ben,

I do not know your system, but in general, you ALWAYS can decrease the PMT
gain if you simultaneously increase the laser power. If this does not work,
there are several points to check:
1) the laser - when you increase the power you should see more light at the
sample (which is obvious)
2) wrong offset setting - a value of zero is usually a good starting point
(at least on Leica's)
3) replace the replacement (as suggested by other members of the list).
4) a VERY peculiar sample, worth a paper in Nature and a milestone in
superresolution imaging (based on nonlinear effect).

You say that with other lasers it works fine. Do you mean the same PMT?
There's no reason why a PMT should work with one color and not the others...

And regarding the stripes, if the pinhole is set properly, ambient light
should not affect the result. The cause may be an unstable laser or
defective detector (or its supply).

Regards,

deden


On Thu, 13 Dec 2012 17:07:52 -0600, Ben Melchior <[log in to unmask]> wrote:

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>http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
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>
>Hi Listers,
>
>I have a technical question regarding the tuning of PMT modules on a confocal 
>system.
>
>We have recently replaced a PMT module on our LSM5 system.  Although we 
>now can get a signal and observe our cells we still having what looks like 
>electrical interferences (horizontal stripes) that impact the quality of our 
>images when scanning.
>The image acquisition now requires a much lower laser power (633nm line) 
>than previous, but inversely, an extreme detector gain was needed (over 
>1100!). If I try to increase the laser power and decrease the PMT voltage it 
>looks like the PMT saturates or there is no more signal.
>Other channels/lines have clean signal. Nothing wrong with the optics.
>
>Is there any electronic engineer or specialist with any thoughts regarding 
>adjustments, tweaking, or calibration of the PMT module? Or any pin on the 
>board that I should check to see if the control voltage to the PMT is right?
>
>Thank you,
>
>Ben