Re: Microwave Optics Experiments

[Stanley A Dodds <dodds@ruf.rice.edu>]

> At 19:51 11/3/97 -0500, you wrote:
> > ... does one purchase blocks of paraffin or do you have to make 
> > them by melting the wax and pouring it into a mold?
> > Brian Oliver

I made such prisms by casting into a sheet metal mold. It was just a
few pieces of aluminum clamped together, filled and then disassembled
to take out the prism. Paraffin shrinks a lot as it cools, so several
small pours are less likely to lead to an internal cavity than trying
to do it all at once. Even so I found the surfaces sufficiently curved
due to strains that I had to machine the finished casting to get a
respectable-looking prism.

The students did two experiments with the prisms: Using one like an
optical prism, measuring refraction of a beam; Using a pair arranged
to allow 'tunneling' between them and qualitatively determining the
transmission as a function of separation. Both exercises work, but not
well. The microwave beams are broad and divergent, so angles are
sloppy and some energy goes around even a big prism. There are also
unwanted reflections and interferences which can be hard to
recognize. We abandoned the exercises because of student grumbling, but
I think they could still be useful as demos if carefully set up.

Good luck in your efforts.

Stan