ABSTRACT
Interference is a phenomenon in which two or more waves are superimposed to give a resultant intensity different from the intensity summation of the individual waves. Interference effects can be observed in all types of waves, including electromagnetic wave, acoustic wave, and matter wave, though our discussion here is limited to the interference of light. In order for light waves to interfere, they should be correlated or coherent with one another. This requires that the waves involved in interference come from the same source or have the same frequency. The principle of interference is equal to the principle of superposition. If a crest of a wave meets a crest of another wave of the same frequency, the resultant amplitude becomes the vector sum of the individual amplitudes. Thus, the two waves must have the same polarization in order to maximize the interference effect. When waves of different polarization are added together, they result in a wave that has a polarization state different from those of the original waves. Interference can be easily observed in our daily life. For example, the colors observed in a soap bubble arise from the interference of light reflecting off the front and rear surfaces of the bubble film. The surfaces of many objects (butterfly wings, sea shells, and some minerals) appear to change color as the angle of illumination or the angle of observation changes. This is often created by the interference of light with surface microstructures. A simple one-dimensional (1D) interference pattern (or fringe) is obtained when two plane waves of the same frequency intersect at a non-zero angle. The resulting fringe consists of alternating bright (constructive interference) and dark (destructive interference) regions. In this case, interference is a kind of energy redistribution process. The energy lost at the destructive interference is regained at the constructive interference. Interference can also occur between multiple beams, once the phase differences between them remain constant over the observation time. Interferometry refers to a family of techniques in which 110waves, usually electromagnetic waves, are superimposed to retrieve certain information. Interferometers are widely used for the measurements of small displacements, refractive index changes, and surface irregularities. Interferometry has made a significant contribution to the advancement of astronomy, spectroscopy, and optical/engineering metrology. Interferometers are generally classified into amplitude-splitting and wavefront-splitting systems. 1–6 In the case of amplitude-splitting, a beam splitter divides a light wave into two beams traveling in different directions, which are eventually combined to produce an interference pattern. In the wavefront-splitting system, a light wave is divided in space through small apertures or narrow slits and the divided waves are allowed to recombine after traveling different paths. Young’s double-slit interferometer is a classic example of the wavefront-splitting system.
