ScanImage 2018 : Diagonal Patterns Appear when PMTs On and Laser Off

When the PMTs are powered on and everything else is dark (laser off, turn the computer monitor off, etc), there is a periodic signal of ~215 kHz (13-14 peaks on one line, line period 63 us or 4.67 us per peak), which causes diagonal patterns to appear on the image.

What is going on and how can this be removed?



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 (as illustrated in the left picture, between -10 and 10), and your image signal values are well above this noise value.


Try changing the voltage on the PMT power supply and observe what happens.