Interference

The wave properties of light lead to interference, but certain conditions of coherence must be met for these interference effects to be readily visible.

Double Slit Interference

Three Slit Diffraction

Three Slit Interference

Fraunhofer Diffraction Geometry

The diffraction pattern at the right is taken with a helium-neon laser and a narrow single slit. Note: To obtain the expression for the displacement y above, the small angle approximation was used.

Soap film sample

Oil film sample

Anti-reflection caoting sample

Interference Maxima and minima

Michelson Interferometer

The Michelson interferometer produces interference fringes by splitting a beam of monochromatic light so that one beam strikes a fixed mirror and the other a movable mirror. When the reflected beams are brought back together, an interference pattern results.

Fabry-Perot Interferometer

This interferometer makes use of multiple reflections between two closely spaced partially silvered surfaces. Part of the light is transmitted each time the light reaches the second surface, resulting in multiple offset beams which can interfere with each other. The large number of interfering rays produces an interferometer with extremely high resolution, somewhat like the multiple slits of a diffraction grating increase its resolution.

Diffraction

Diffraction manifests itself in the apparent bending of waves around small obstacles and the spreading out of waves past small openings. Diffraction reveals the geometry of the diffracting object.

Fraunhofer Diffraction Geometry

The diffraction pattern at the right is taken with a helium-neon laser and a narrow single slit. Note: To obtain the expression for the displacement y above, the small angle Approximation was used.

Fresnel Geometry

For the Fresnel case, all length parameters are allowed to take comparable values, so all must be included as variables in the problem. The usual geometry assumes a monochromatic slit source and the problem is set up in terms of a parameter v as defined below. This parameter is used with the Cornu spiral or a table of elliptical integrals.