The basic principle of Newton's ring interference: Newton's ring device is composed of a flat convex surface with large curvature radius placed on an optical glass plate (plane mirror). The thickness of the air layer between the convex surface of the plano-convex lens and the glass plate gradually increases from the center to the edge. If the parallel single light shines vertically on Newton's ring, there will be optical path difference between the two beams reflected from the upper and lower surfaces of the air layer, and they will interfere when they meet the convex surface of the plano-convex lens.

The interference pattern seen from the lens is a series of bright and dark rings centered on the glass contact point, called Newton's rings. The thickness of air layer is the same everywhere on the same interference ring, which belongs to equal thickness interference.

Interference phenomenon is one of the strong evidences of light wave theory. When the sun shines on the soap bubbles or oil films on the water surface, the colored stripes are the interference phenomenon of light. In order to produce interference, two beams of light must meet the coherence conditions: the same frequency, the same vibration direction and constant phase difference.

There are generally two methods to obtain coherent light in experiments: wavefront splitting and amplitude splitting. Equal thickness interference belongs to fractional amplitude method. /kloc-At the beginning of the 7th century, physicist Newton happened to find that when a convex lens with a large radius of curvature was placed on a flat glass, its contact point showed an alternating pattern of light and dark rings, which was the phenomenon of light interference. This optical phenomenon is called "Newton's ring".

Because Newton insisted on the particle theory of light, he could not explain it clearly. The interference of Newton's ring is applied to the measurement of sphericity, flatness and smoothness of materials.