Last week I was able to set up the Michelson Interferometer correctly and obtained the desired annular interferences. This is a huge accomplishment to me because I had been having so much trouble aligning all the optical devices.
The biggest issue I was having is that I have never had this much exposure to optical devices before. Sure, I did have some experience from a class but it was much simpler than this real life application work I am doing in lab now.
For example, an obstacle I had to overcome was that the height of the adjustable mirror was bigger than the height of the beam. Below is a diagram of how I fixed this issue:
First, I placed a mirror at 135 degrees ( if you were looking at a unit circle) and made sure that the reflected beam was well aligned. Then I placed another mirror at 45 degrees and made sure that the twice reflected beam was well aligned as well. Using the knobs on the mirrors that introduce angle shifts, I aligned the reflected beam to be at the center of the adjustable mirror.
My new input would be at an appropriate height. From here on out I just calibrated and aligned the rest of the Michelson Interferometer.
The number of fringes depends on the difference in path lengths the two arms go through. As a reminder, here is the diagram of the set up:
The number of fringes observed decreases as the difference in distance of m1 and m2 from the beam splitter also decreases. In other words, if m1 and m2 are at the same exact distance from the beam splitter then we will have very few fringes.
If we introduce the phase plate just before the m2, a different path length would be traveled through the pi part and the 0 part of the phase plate. This is because the pi part of the phase plate has an additional deposition, which means an additional layer the light must pass through. So what we would expect to see is annular fringes that are not symmetric.
Here is what was observed:
This is exactly what we were hoping for !! but we also encountered some other strange interferences.
Like this one:
The interference pattern shown above was off to the right of the main interference we were looking for. We tried to look for the source of it, but we could not localize it.
here is a better image of it:
We can see that on the persons hand to the left some additional interference patterns are showing.
We are not sure where these additional interference are coming from, but a while ago when I was doing my power and polarization measurements I noticed something interesting. When the laser beam was incident onto the phase plate, the output light on the pi-phase had dispersed. Instead of only seeing one beam, I observed a main beam of light and a couple of other ones next to the main one. They were pretty intense relative to the main beam since I was able to see them with the OD glasses I was using.
We made a note of this, but maybe this is where the additional interferences are coming from?
The graduate student I am working with also mentioned something about light coherency and that a possible solution would be placing m1 and m2 farther from the beam splitter. At a much bigger distance than they are now. I am not completely sure how this works out, but I do plan on getting some clarification.
That’s it for now folks,
Till next time !
Physics and other weird things 