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When the PMTs are powered up, with everything else turned off (laser off, turn the computer monitor off, etc), there seems to be a periodic signal of ~215 kHz (13-14 peaks on one line, line period 63 us or 4.67 us per peak), which causes funny diagonal patterns to appear on the image, see picture below. The left is the green PMT, the right is the red PMT. The graphs are intensity profiles of horizontal lines across each image.

Have you ever heard about this issue from your users?

Any idea what is going on / how to get rid of it?

This is a normal situation and is expected. There is a certain amount of noise introduced into the system by the PMT power supply that will always be there. This is ok if the noise is low, and your image signal values are well above this noise value.

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For more information, see the Hamamatsu PMT Handbook, Section 8.2, 'Characteristics of Power Supply Circuits'

 

 

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