interferometer

[Ken Olum <kdo cosmos phy tufts edu>]

Hi, all. The interferometer seems very good.  Here's a picture of it set 
up:
http://physicstheorynet.org/interferometer.jpg
and here's the interference pattern:
http://physicstheorynet.org/interference-pattern.jpg

The mirror on the bottom has can be adjusted to get the center of
interference pattern on the screen.  The mirror on the left has a
micrometer that you can use, for example, to determine the wavelength of
the laser by seeing how many fringes correspond to a 50 micron change
in path length.

I put a photosensor in the center of the interference pattern and
connected it to a a sound system, and I was able to speak near the
mirror and have my voice translated into path length change, fringe
position, photosensor current, audio signal, and back to sound.

I also tried holding an ice pack over one of the beams and I immediately
got large changes in the interference pattern due to the different index
of refraction of the colder air.

It came with many experiments, which I have not tried:

-> Determine index of refraction of a plexiglass plate by changing the
amount of the path in the material by rotation.
-> Determine the expansion coefficient of an aluminum bar by putting
one of the mirrors on the end and heating the bar.
-> Spectrometry of the laser (it emits several closely spaced lines) by
looking at contrast changes.
-> Red and white light interference with LEDs.

I'm storing the interferometer set up in a plastic box, with all the
rest of the equipment separate.  This allows it to be stored and
transported without the components getting bumped or dusty.

The pictures above are taken with the document camera.  It seems to do a
good job, though the interference pattern looks better by eye than it
does in the picture.

Let me know if you'd like to use it.

                                        Ken