Laser Speckle Removal??

[dde...@interserv.com]

I am trying to produce a circular diffraction pattern by collecting laser light reflected from a diffuse
object and passing in through a large pinhole (.5 mm). Unfortunately, I am unable to see the diffraction
pattern due to a speckle pattern resulting from the coherence of my HeNe laser.

If anyone knows how to remove this speckle pattern without disturbing the diffraction pattern due to
the pinhole, then please let me know. I have already reduced the size of the illuminating laser spot, and
therefore, have reduced the number of diffuse reflectors which can contribute to the speckle pattern.
Any advise is welcome.

[David Entenberg]

I believe that one of the best ways to eliminate the speckle with out
affecting the pattern, is to spin the screen on which you project the
pattern. (saw this done in a zygo interferometer).

"Pumping, sometimes vigorous pumping,
is needed to produce the `unnatural'
condition of population..."
Pedrotti & Pedrotti
page 433

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[BillyFish]

dde...@interserv.com wrote

***********

I am trying to produce a circular diffraction pattern by collecting
laser light reflected from a diffuse
object and passing in through a large pinhole (.5 mm). Unfortunately, I
am unable to see the diffraction
pattern due to a speckle pattern resulting from the coherence of my HeNe
laser.

If anyone knows how to remove this speckle pattern without disturbing
the diffraction pattern due to
the pinhole, then please let me know.

*************

Use milk or some liquid latex material for your diffuse reflector. If you
need to illuminate an object, illuminate with light scattered off of the
milk.

Speckle comes from a fixed in time but variable in space. With scattering
from small particles (colloidal particles) you get time averaging of this
phase variation, and the speckle disappears.

William Buchman

[David Knapp]

i...@huey.udel.edu (Charlie Ih) wrote:

>In article <Pine.SUN.3.91.951011...@mathlab.sunysb.edu> David Entenberg <da...@mathlab.sunysb.edu> writes:
>>On 10 Oct 1995 dde...@interserv.com wrote:
>

> > I am trying to produce a circular diffraction pattern by collecting laser light reflected from a diffuse
> > object and passing in through a large pinhole (.5 mm). Unfortunately, I am unable to see the diffraction
> > pattern due to a speckle pattern resulting from the coherence of my HeNe laser.
> >
> > If anyone knows how to remove this speckle pattern without disturbing the diffraction pattern due to

> > the pinhole, then please let me know. I have already reduced the size of the illuminating laser spot, and
> > therefore, have reduced the number of diffuse reflectors which can contribute to the speckle pattern.
> > Any advise is welcome.
> >
> >
>>I believe that one of the best ways to eliminate the speckle with out
>>affecting the pattern, is to spin the screen on which you project the
>>pattern. (saw this done in a zygo interferometer).
>

>If you want a simple and quick method, a rotating (moving) diffuser
>screen (ground glass, "magic tape", etc) is the answer. However, the
>S/N is only about 10 - 20. The most effective method I know, though more
>complicated, is described in the following articles. The S/N can
>exceed 100. I hope this will help.
>
>
>1. C. S. Ih, "Speckle Elimination Using Random Spatial Phase Modulation",
> Applied Optics, 16, 1473-1474 (June 1977).
>
>2. C. S. Ih and L. A. Baxter "Improved Random Spatial Phase Modulation
> for Speckle Elimination, Applied Optics, 17, 1447-1454 (May 1978).
>
>Charles S. Ih
>Uviniversity of Delaware

Charles,

Are the references you've given referring to active laser cavity modulation?

--
David Knapp
Energy and Minerals Applied Research Center (EMARC) (303) 492-7113
Department of Geology http://lolita.colorado.edu/david1.html
University of Colorado, Boulder da...@lolita.colorado.edu