subject: NEWTON RINGS [print this page] destructively interfere. destructively interfere.
The radius of curvature R is found by counting the number of bright fringes to a radial distance rm, where the first bright fringe is m=0.
The classic Fizeau interferometer is useful for checking the curvature of a lens surface versus a master surface, as in lens grinding. The surfaces match when only tilt fringes remain.
he light rings are caused by constructive interference between the light rays reflected from both surfaces, while the dark rings are caused by destructive interference. Also, the outer rings are spaced more closely than the inner ones. Moving outwards from one dark ring to the next, for example, increases the path difference by the same amount, corresponding to the same increase of thickness of the air layer/2. Since the slope of the lens surface increases outwards, separation of the rings gets smaller for the outer rings.There is light incident on the flat plane of the convex lens which is situated on the optically flat glass surface below, the light passes through the glass lens until it comes to the glass-air boundary, here the light goes from a higher refractive index (n) value to a lower n value. The light passes through this boundary and suffers no phase change. Also at this boundary, some light is transmitted into the air and some light is reflected. The light that is transmitted to the air travels a distance t before it is reflected at the flat surface below, the air-glass boundary causes a a half-cycle phase shift because the air has a lower refractive index than the glass. The two reflected rays now travel in the same direction to be detected. The convex lens touches the flat surface below and from this point
