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| laser... |
 Posted: Thu Oct 15, 2009 1:17 pm |
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Guest
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does anyone know how to define "astigmatism measurement" of guassian
beam which is invariant via optics?
if you have any reference that you can suggest, it will be great, too. |
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| I.N. Galidakis... |
| Posted: Thu Oct 15, 2009 7:12 pm |
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Guest
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laser wrote:
[quote:f1947104b7]does anyone know how to define "astigmatism measurement" of guassian
beam which is invariant via optics?
if you have any reference that you can suggest, it will be great, too.
[/quote:f1947104b7]
1) Photograph the beam target against some dark background.
2) Convert target to black and white.
3) Slice through the target image at n different angles (say at angles a =
2*k*Pi/n, k=0,1,2,...n-1, with respect to the x-axis) with Iris or any other
spectral tool to produce two-dimensional distributions G(a) of the target spot
for all angles a.
4) You know the sliced distributions G(a) should all be Gaussian, so interpolate
each one of them by finding suitable mu(a) and sigma(a) for G(a) to match the
distributions on 3) as close as possible.
5) use regression analysis (or least squares or any other approximation) to
examine the deviation of G(a) from being purely Gaussian.
If the error is small in all of them there's no beam astigmatism. If there's any
astigmatism, some of your distributions G(a), a in {a_1, a_2, a_3,...a_p} will
not be Gaussian. You can then say that the beam suffers astigmatism at angles
a_1, a_2,... a_p.
--
Ioannis |
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| Jürgen Appel... |
| Posted: Sun Oct 18, 2009 6:00 am |
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Guest
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I.N. Galidakis wrote:
[quote:9eb29b0c33]If the error is small in all of them there's no beam astigmatism. If
there's any astigmatism, some of your distributions G(a), a in {a_1, a_2,
a_3,...a_p} will not be Gaussian. You can then say that the beam suffers
astigmatism at angles a_1, a_2,... a_p.
[/quote:9eb29b0c33]
This is not correct. You very well can have astigmatic beams where each
intensity slice (as well as the cross sections) are Gaussian; actually this
is the case for _every_ Gaussian beam by definition. Even more puzzling
might be that you can even have Gaussians of the same width for all
directions and nevertheless have astigmatism.
In
http://www.ucm.es/info/euoptica/org/pagper/jalda/docs/libr/laserandgaussian_eoe_03.pdf
you can find some more information about all the nasty properties, that even
an general astigmatic Gaussian laser beam can have. Maybe the references in
there help you to find your answers.
Cheers,
Jürgen |
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