Posted by
Michael Giacomelli on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Re-Preamplifier-for-fast-point-scanning-tp7583751p7583756.html
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Hi Peter,
Those artifacts are indeed caused by the AC coupling. A bright signal
causes a shift of the zero level that persists for some time
afterwards. You can however remove them with digital filtering by
treating the data you record as an AC signal modulated at 80 MHz with
the intensity of your image encoded in the envelop.
For what its worth, Thorlabs has begun selling their TIA-60 product
(previously you could get it only with a complete system), which is
specifically designed for fast MPM imaging with the H7422:
http://www.thorlabs.de/newgrouppage9.cfm?objectgroup_id=8862We have several of these, and while they do roll off a little before
80MHz, their performance is excellent and they are reasonably priced.
They are also DC coupled and, provided you use the included cabling,
are quite stable with an H7422. I would strongly recommend this part
for an 80 MHz system. Its not worth paying more unless you have a
very high rep rate system.
Mike
On Wed, May 13, 2015 at 11:29 AM, Peter Rupprecht
<
[hidden email]> wrote:
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> To join, leave or search the confocal microscopy listserv, go to:
>
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>
> Dear List,
>
> this is a follow-up on my earlier post some months ago:
>
http://confocal-microscopy-list.588098.n2.nabble.com/Preamplifier-for-fast-point-scanning-td7583344.html>
> Shortly after this post, I tested the ACA-4-40 preamplifier from Becker&Hickl and compared it directly to the Femto DHCPA-100. Amplification and noise seemed to be in the same order of magnitude for both products for my setup. Although performance might be also dependent on bandwidth of PMT and other details that I cannot test properly. I realized that comparing the two products objectively would involve more than just one experimental setup.
> The one annoying thing that was also mentioned before by Michael, seems to be the AC-coupling of the preamp. At least this is how I interpret the strange artifacts that I see in the wake of very bright objects. This is very clearly visible when scanning bidirectionally, because then this artifact clearly shows the scanning direction.
> Here is an excerpt of an image which shows how this may look like for calcium imaging (this is averaged over a couple of frames); please note the picture titles:
>
https://www.dropbox.com/sh/bwxxjrw44yxxb0p/AAAM9yWeMMc37NT_VORDEiaBa?dl=0>
> Based on my limited experience, I would conclude that the B&H ACA is maybe better for photon counting or flourescence lifetime imaging (due to higher bandwidth), but not the appropriate solution for my calcium imaging experiments.
>
> Peter