Desktop Michelson-Morely Interferometer

Step 4 The Arrangement

I used a sheet of 6mm thick polycarbonate plastic as the 'optical bench'. It fails quite well in that role, and in a sense, that's a good thing - as it allows one to observe the effect of *tiny* deformations on the intereference pattern produced.

Here's the arrangement.

Now, this all looks very pretty, but the point to observe is the striped pattern at the bottom of the picture.

This is the interference pattern generated by the two rays, and it is an incredibly finicky thing to establish - expect a good half hour of gently poking and tilting the elements till you glimpse this faint but unmistakable banding.

That is being projected onto an almost-horizontal piece of white card. I tilted the card so that the interference pattern would be broadened out and the fringe motion would be more readily observed.

The second picture is a contrast boosted view of the image on the white card.

In the movie you can see the effect of gently poking the polycarbonate 'bench' with a bit of heat-shrink sleeving (I'd have used a feather, but I'm fresh out of them).

What you're seeing is the weak and feeble tubing bending the 6mm polycarbonate. You can't see it actually deflect, but you're altering the relative path lengths of the two legs of the interferometer.