Date: Fri, 02 Feb 2001 11:23:26 -0800

Author: "Bernard G. Cleyet & Nancy Ann Seese"

Subject: Re: Michelson Interferometer problems

Post:

Do any of you use a spatial filter (for this use)-- I never checked the
diff., because all our expanders included one.

bc



Steve Wonnell wrote:

> Scott,
>
> I also do 1 and 2 below, also we use a 15 mW laser for our
> auditorium, as Marty says, the 1 mW is pretty faint.
>
> Steve
>
> On Fri, 2 Feb 2001, Martin Simon wrote:
>
> > 1. First align without expanding the laser beam. (Make sure
> > the beam is going in the correct direction. I have seen people
> > set it up with the beam going into the output and this makes
> > things more difficult. The input beam usually has a straight
> > shot to the adjustable path length mirror.) Set up so the beam
> > hits approximately the centers of the mirrors. At the output,
> > you will see multiple dots due to the multiple reflections. (I
> > can usually see 6 dots.)
> >
> > 2. Overlap the corresponding bright dots. You should see fringes
> > crossing the overlapped dot. Keep adjusting the overlap until
> > you do. When you see fringes make fine adjustments so that the
> > fringes are as widely spaced as possible. You may see only one
> > fringe in the dot when this is done. The fringe spacing may be
> > larger than the dot.
> >
> > 3. Now put the beam expander between the laser and the interferometer.
> > Only expand the beam to just fill the mirrors. Like others, I use
> > a little spherical lens which makes a diverging beam. This gives
> > a Bulls eye pattern on the viewing screen which is called a Fresnel
> > zone plate. It is like a hologram of a spherical lens. If the pattern
> > isn't centered you can do some fine adjustment to center the pattern.
> > If you see fine line fringes instead of the Bulls eye, take out the
> > beam expander and start the alignment again with number 2 above.
> > If you expand the beam to truly parallel rays, I think you will
> > see parallel line fringes instead of the Bulls eye pattern described
> > above.
> >
> > >I am using a standard HeNe laser (1mW, I believe)
> >
> > With a 1 mW laser the pattern is going to be very faint and probably
> > not viewable in a lecture hall. Use the most powerful laser you have.
> > I use a 15 mW HeNe to project for a class and it is pretty faint in the
> > classroom. I would like to improve it.
> >
> > Martin Simon
> >
> >
> k

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