Re: [ATM] coherence length

["Bob May" <rmay@nethere.com>]

As I understand it, coherence length is the distance it takes for
the two frequencies to get to the point where the minima of one
of them matches the maxima of the other.   Past that point, you
end up with recurring points along the light path where this
happens as well as points where the maxima of the two match and
you'll be getting strong fringes.  There is a interfrometer that
I saw at Stellavane where the path length was adjustable so that
you can make sure that the coherence length is right for the
laser to make strong fringes from the tested mirror.
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net

----- Original Message -----
From: Carlos Davila <comunerito@gmail.com>
To: <atm@atmlist.net>
Sent: Tuesday, May 27, 2008 6:47 PM
Subject: [ATM] coherence length


> Hello,
>
> The book "Introduction to Modern Optics" by Fowles, discusses
> coherence length, which is the path difference between two
beams of
> "quasimonochromatic" light for which interference fringes can
no
> longer be seen...that is, any path difference exceeding the
coherence
> length produces no fringes. Are there any ballpark values for
the
> coherence length of different objects one might view through an
> astronomical telescope? Are we talking on the order of
wavelengths,
> tens of wavelengths...or meters? How do these compare to
coherence
> length due to atmospheric turbulence?
>
> Thanks,
> Carlos
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> ATM mailing list http://www.atmlist.net/
>

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