![\"rip\"](\"http:\/\/labrigger.com\/blog\/wp-content\/uploads\/2016\/05\/rip.png\")
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Andrew Lim<\/a> wrote in to discuss strategies on dealing with ripple noise in 2-photon imaging systems, particularly when using resonant scanners. He writes:<\/p>\n This isn\u2019t so much a tip as a problem with resonant two-photon scopes that several people have told me they also have but I haven\u2019t seen a solution for (other people apparently just ignore it). I wonder if you could raise the issue on the blog to see if people have ideas, or if you know of a solution, maybe you could post it?<\/p>\n Apparently the GaAsP PMTs from Hamamatsu (like all PMTs) have a certain amount of ripple noise stemming from the high voltage power supply in the PMT, in the frequency range of 200-300 kHz. On a resonant two-photon, when the PMTs are on but not receiving any light, this shows up as oscillations in the signal on each line of the image, and because the frequency of the ripple noise doesn\u2019t exactly match the time it takes to scan each line, these oscillations show up as diagonal patterns on the image. If the signal is bright enough, these patterns don\u2019t really matter, but if you are trying to image something dim, the patterns can obscure the image.<\/p>\n One solution could be to remove the oscillations in post processing: since they are regular, one should be able to undo the Sanderson correction, detect the frequency\/phase of the oscillation, and just subtract the ripple noise. But before embarking on this project, I wanted to find out if anyone else might have done this already, or have better ideas.\n<\/p><\/blockquote>\n Hamamatsu shares this information<\/a> on the ripple: Jeff Stirman<\/a> shares his thoughts on this: <\/p>\n \nI have noticed this ripple noise as well when imaging dim objects and it can be quite annoying. However, I never saw this when I was performing acquisition in photon counting mode. Also, more recently we have moved to somewhat of a hybrid analog photon counting mode and again I do not observe this. To clarify: I do not see this when my discriminator level is set to an amplitude that exceeds the ripple. For both photon counting and analog photon counting (see Moon et al, \u201cAnalog single-photon counter for high speed scanning microscopy\u201d, Optics Express, 2008<\/a>) a discriminator is used after the amplified PMT signal. The output from the discriminator can either by counted directly by a high speed counter, or can be digitized (analog integration). We do the latter because we did not find a counter of sufficient speed. (We are performing discrimination for demultiplexing purposes.) When the level of the discriminator is set higher than the level of this ripple noise, then it is effectively filtered out. Of course if your signal is on the same order as this ripple noise, then it too is filtered, but we always have signal > ripple so it is effectively filtered.\n<\/p><\/blockquote>\n","protected":false},"excerpt":{"rendered":" \n
\n![\"hm\"](\"http:\/\/labrigger.com\/blog\/wp-content\/uploads\/2016\/05\/hm.png\")
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