Posted by
Andrew York on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Two-photon-microscope-questions-tp7583010p7583014.html
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Short answer to (1) is, astigmatism.
Transmission through a flat, tilted piece of glass gives only a lateral
deflection to a collimated beam, but it gives astigmatism to a focusing
beam. You could imagine using a dichroic that reflects the excitation
rather than transmitting it, but be careful about flatness (most dichroics
are quite curved, sadly) which can also give astigmatism.
Because of some bad decisions, I ended up using a dichroic in the same
manner you describe. You can cancel a lot of the resulting astigmatism with
a second piece of glass tilted the same amount but rotated 90 degrees about
the optic axis. On the other hand, why bother solving a problem you don't
have to have?
On Sat, Nov 29, 2014 at 11:23 AM, Heping Yuan <
[hidden email]> wrote:
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>
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>
> Hi everyone, I was looking to modify an old confocal system into a
> two-photon system. I
> had two questions and would appreciate any help.
>
> 1) A section of the schematic of typical two-photon is as follows
> (
http://www.thorlabs.com/tutorials.cfm?tabID=32729):>
> Galvos -> Scan Lens -> Tube Lens -> Dichroic (690 LP) -> Objective
>
> where fluorescence emission is reflected off Dichroic towards a collection
> lens and PMT's
>
> I'm wondering if there are some unforeseen problems in changing the order
> as follows:
>
> Galvos -> Scan Lens -> Dichroic (690 LP) -> Tube Lens -> Objective
>
> where the tube lens can focus the fluorescence emission back to the
> Dichroic and directly
> into the PMT's (without a collection lens).
>
> 2) What is a common procedure to image the back aperture of the objective
> to the input
> window of the PMT? My first thought is to create a collimated source with
> size > than
> back aperture and shine directly into the back aperture with objective off
> (to see spot size
> at PMT input). Would this be correct? If so, practically speaking what
> type of source is
> typically used?
>
> Thanks,
> Heping
>