I’ve been studying Newton’s rings and I’m confused as to why the fringes can only be viewed at the surface of the top mirror.
In the case of point source interference, we know that fringe interference occurs in any plane.
In the case of an extended source, it appears that the interference generally occurs only at infinity.
However, in the case of Newton’s rings — that is, extended sources at an angle to each other —, they only occur in the plane of that angle.
Many thanks for any insight.
