How is the interference phenomenon manifested and observed?

In physics, interference is a phenomenon that two or more waves overlap in space to form a new waveform.

For example, if a monochromatic beam is divided into two beams by a beam splitter, and then they overlap in a certain area of space, it will be found that the light intensity distribution in the overlapping area is not uniform: its brightness changes with its position in space, and the brightness in the brightest place exceeds the sum of the original two beams, while the brightness in the darkest place may be zero. This redistribution of light intensity is called "interference fringe".

When two waves propagate in the same medium and overlap, the particles in the medium within the overlapping range are simultaneously acted by the two waves. If the amplitude of the wave is not large, the vibration displacement of dielectric particles in the overlapping range is equal to the vector sum of the displacements caused by their respective fluctuations, which is the so-called superposition principle of waves. If the peaks (or valleys) of two waves reach the same place at the same time, they are said to be in phase at this point, and the interference wave will produce the maximum amplitude, which is called constructive interference; If the peak of one wave and the trough of another wave reach the same place at the same time, it is said that the two waves are in opposite phases at this point, and the interference wave will produce the smallest amplitude, which is called destructive interference.

Observation instrument

In order to obtain a coherent light source that can observe visible light interference, people invented and manufactured various optical devices and interferometers that produce coherent light. At that time, these interferometers all had very high measurement accuracy: Albert Michelson completed the famous Michelson-Morey experiment with the help of Michelson interferometer, and got zero results in observing the etheric wind. Since the 1960s, the invention of laser, a high-intensity coherent light source, has made optical interferometry widely used, and laser interferometers can be seen in all kinds of precision measurements. Now people know that the interference of two kinds of electromagnetic waves is the result of superposition of mutually vibrating electric field intensity vectors, and due to the wave-particle duality of light, the interference of light is also the result of superposition of photon's own probability amplitude.