michelson morley interferometer project help

[paul1598419]

I thought it would be difficult to do. Have you tried adding a lens to spread the spot out more? Add it after the beams have been combined and see what that does for you.

 

[Davidlang]

When I used the larger laser I did place a Plano concave lens after It left. With the small laser It spread well on Its own the video of the hyperbola was done without a lens. I was even able to see several fringes when the mirrors were further misaligned.

 

[paul1598419]

If you are interested in knowing the coherence length of your lasers you can find out by moving the mirror until the fringes disappear. The distance the mirror moves times 2 is equal to the coherence length of the laser.

 

[Davidlang]

From what I understand the coherence length determines how far out of alignment the mirrors can get and still show fringes. Does it also affect the results when the mirrors are close to equal? The small laser is about 6”. I am still trying to figure out why it wouldn’t go black. I assumed the problem might be coherence length, beam spread, or it being randomly polarized. In the video the guy was using a 35mw polarized spectra physics 127 hene laser. The laser I got to go dark was a 24” polarized hene and the beam didn’t spread like the small one.

 

[paul1598419]

I can't really say why your 6 inch HeNe spreads without a lens. I have one and it stays very collimated and doesn't spread much at all. It sounds like there might be an alignment problem with your laser.