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Hi Peter

The 37dB ACA model is worth trying, although its not really ideal.
Just be careful with source capacitance and cabling or you will get
oscillation because of the extremely high gain bandwidth product.  Was
really hoping someone would point out something better suited though.

GVD in typical 50 ohm RG-58 cables usually isn't a huge problem
because the attenuation is low enough below 1GHz and most timing
applications aren't sensitive at that level, so if you match cable
lengths, your pulse and timing will be relatively unaffected.  GVD
becomes problematic near frequencies with attenuation, so it tends to
be a bigger problem if you add filters to a system (or amplifiers with
too little bandwidth).  If you buy the ACA and intend to lowpass
filter it, look carefully at the minicircuits datasheets before
ordering, they are quite good about specing those things.  If you're
running impedance mismatched (e.g. 50kOhm terminating resistor), you
are just trading off bandwidth for a larger signal.

Mike


On Tue, Feb 3, 2015 at 2:22 PM, Peter Rupprecht
<[log in to unmask]> wrote:
> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hi,
>
> Thanks for the replies!
>
>
> Actually, I'm quite surprised that this fast PMT preamplifier seems to be rather uncommon. When somebody uses a 8 kHz resonant scanning confocal microscope at the lowest zoom, he might want to have not 512x512 pixels, but 2048x2048 pixels or even 4096x4096 pixels. That's not always useful for time-lapse imaging (as Zdenek pointed out), but very useful for taking a single picture or a z-stack with a lot of averaging. And to resolve 4096 pixels at a 8 kHz-scanned line (63 us for one line), you have to sample at ca 80 MHz.
>
> Right now, I'm sampling at 80 MHz, and only when I do not need the full 4096 pixels, I bin it down in the software. But even for functional imaging, sometimes a very big picture - like 2048x512 - can be very useful.
>
> Today, by coincidence, I called Becker&Hickl, and most likely I will test one of their ACA amplifiers side to side to the preamp that I'm using right now. (I was planning to take the 37dB preamp.) Becker&Hickl are specialized on photon counting technology, so this will be rather an abuse of their preamp. I will report the results in some weeks, if somebody is interested.
>
> @Zdenek: A SNR of 3.5 or a little bit more might be enough for some applications ... I was planning to measure the photon count per pixel (using this method :
> http://labrigger.com/blog/2010/07/30/measuring-the-gain-of-your-imaging-system/ ), but I always was busy with other things, so I cannot give you numbers for my imaging system.
>
> @Craig: Are you possibly talking about this amplifier:
> http://www.hamamatsu.com/jp/en/C9663/index.html ? Are there any drawbacks, and can you compare it to other amplifiers?
>
> Michael wrote >> You can have a lot of cabling and amplification in your system so long as you are careful to manage GVD.
>
> This is a little bit off-topic, but until now, I was simply sticking BNC cables with a 50 kOhm sign together, hoping that this would do it... however, I have the feeling that I get some lowpass-filtering / GVD of my detection signal. Do you have any tips for how to check and minimize the system's GVD?
>
>
> Best,
> Peter