Re: Astigmatism aberration as a function of distance

Posted by Michael Giacomelli on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Astigmatism-aberration-as-a-function-of-distance-tp7582827p7582828.html

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Hi Lu,

In an on axis system like you have drawn there should be no astigmatism if
the fiber is well centered on the optic.  Assuming you've correctly aligned
the collimator, I would think it is some other aberration you are seeing.

Regarding your questions in that linked page:

1)  It depends on what you want to collect.  4f (or some other imaging
condition) will give you maximum light collection, which is likely what you
want if you have selected a multimode fiber.  Alternatively, if this is a
confocal system, it is probably not necessary.

2)  The diagram shows a collimated single mode fiber.  That should be
independent of distance.  If you find that your spot is changing rapidly
with distance, likely something is wrong with the collimation.  What are
you using a collimator?  Is it suitable for the NA and wavelength/bandwidth
of your source?  Is it well aligned?  What is the exact model of fiber you
are using.

3)  Most likely it is a problem with your coupler.

Mike

On Tue, Nov 4, 2014 at 11:36 PM, Yan, Lu <[hidden email]> wrote:

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> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
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>
> Hi folks,
>
> I am building a fiber based confocal microscopy setup (with sample stage
> scanning). But I always got some astigmatism aberration in PSF measuremnts.
> The similar aberration was there even I replaced the objective lens with a
> regular lens and imaged my illumination beam through that lens with a
> camera. I got elongated beam 'spot' on both sides of the focal plane, and
> the orientation of the two 'spot' were orthogonal. I think that is
> astigmatism aberration if I am not mistaken. I draw a schematic in Evernote
> so I can include it here. Here is the link:
>
> https://www.evernote.com/shard/s275/sh/55130807-98d4-4748-a4a9-64d19650b695/be0756284a13da18fe6d1f7f419cbcfe
> (copy and paste if the link does not work in email)
>
> I tried to adjust both lens in xy to avoid off-axis incident, but the
> aberration would go away. So I got confused where they came from. I hope
> someone here could lead me a direction to further look into it.
>
> Thanks very much,
> Lu
> -----------------------------------------------------
> ​​
>
> Lu Yan
> Nanostructured Fibers and Nonlinear Optics Laboratory
> Electrical and Computer Engineering
> Boston University
> 8 St. Mary St., Boston, MA, 02215
> [phone]
> -----------------------------------------------------
>