# Need some help trying to understand the Michelson interferometer

1. Nov 28, 2013

### Acid92

Refer to the second diagram on this website
http://electron6.phys.utk.edu/optics421/modules/m5/Interferometers.htm

Using monochromatic light at first, you produce an interference pattern using the Michelson interferometer. If you set the relative tilt of the mirrors so that they are relatively parallel, the fringes are circular (I understand that this is because of the symmetry in the path length difference between the two sides of the interference pattern) but if you adjust the relative tilt, you get fringes that are arcs. By adjusting the position of the mirror that you can move backwards/forwards, you can control the path difference (and so the distance between the bands in the interference pattern), however, at some point, the circular arcs "reverse" and apparently this indicates that you have moved through path difference d = 0, why? I intuitively understand that this probably has something to do with how reflection works with mirrors but I can't quite explicitly explain it.

Secondly; if you use white light as a source: for a very small range around d = 0, you get a band of colors as an interference pattern. Why is this range relatively small for white light in particular (as compared to monochromatic light) and also, is there any particular pattern in the color patterns of the band, i.e. can you generate specific color arrangements and what do they depend on? Or is it just random constructive/destructive interference for different colors as with interference in thin films?

Heres an example of a white light interference pattern

2. Nov 28, 2013

### Simon Bridge

1. iirc. It's an effect of the same symmetry that produces the circular fringes.

2. "monochromatic" means only one color - so you cannot get a band of colors. As with youngs interference, the separation of the maxima depends on the wavelength - i.e. the color - if the light.