The Michelson Interferometer

It has been about 4 work days since I have attempted to align the Michelson Interferometer. It took a lot of tedious little adjustments to finally get it to work but I think I did it !

Here is a very simple diagram of the set up and of the different interference patterns that can be created:

• 

• 

Let us talk about the set up shown in Figure 1. First, the light beam gets split up approximately 50% and 50% (red light ray) . A fixed mirror, m1, is then set up perpendicular to the beam so that the light beam traces back where it came from (green light ray) . The angle of the beam splitter also causes half of the light to get reflected on to a screen. An adjustable mirror , m2, is also set up so that it is also perpendicular to the red light ray. Half of the light gets reflected back to the light source and half transmits through the light beam and is incident onto the screen ( blue light ray) . I also used a lens to expand the beam before it went into the beam splitter!

The light beam gets split into two parts initially and then brought back together at the screen. The difference in path lengths of the two beams causes an interference pattern.

The thing is that if m1 and m2 are not exactly perpendicular, then the output interference will be as shown in figure 2 labeled b. The interference will be horizontal or vertical straight fringes. if the 2 mirrors are exactly perpendicular to each other we will get annular shaped interference.

Trying to get the two mirrors to be exactly perpendicular WAS SO HARD!! I spent hours trying to align them. I finally did it C’:

Here is the interference pattern I was looking for:

• 

Isn’t it beautiful c’: ? It is not perfect, as we can see not all of the rings are in the view of point. To fix this, the angle of the beam splitter was adjusted. I also need to make sure that m1 and m2 are at the same distance from the beam splitter.

This is the feedback I got from my graduate student and my advisor but besides that everything is looking good !

I am kind of nervous about moving the mirror to make sure that they are at the same distance because I do not want to introduce an angle shift between the two mirrors :c

which me luck y’all !