The superposition of two (or more) waves of the same kind that pass the same point in space at the same time is called interference. If the waves are in the same phase, e.g. crest on crest, their amplitudes combine to produce a strong wave. This is called constructive interference. If the waves are out of phase, e.g. if crests of one are superposed on the troughs of another, we get destructive interference.
Light falling on thin films is reflected twice, once from the upper surface and once from the lower surface. Light rays from the two surfaces produce constructive and destructive interferences (or produce interference patterns). Beautiful colours seen in soap bubbles and oil films on water are produced due to the interference of white light reflected by these surfaces.
Perhaps the most exciting illustration of interference is found in holography, which is the technique of recording and reproducing three dimensional images. A laser beam partly reflected from an object and partly from a mirror produces interference fringes on a photographic plate, which then becomes a hologram. When laser light is transmitted through the hologram, one can see a three dimensional virtual image of the object.
Light falling on thin films is reflected twice, once from the upper surface and once from the lower surface. Light rays from the two surfaces produce constructive and destructive interferences (or produce interference patterns). Beautiful colours seen in soap bubbles and oil films on water are produced due to the interference of white light reflected by these surfaces.
Perhaps the most exciting illustration of interference is found in holography, which is the technique of recording and reproducing three dimensional images. A laser beam partly reflected from an object and partly from a mirror produces interference fringes on a photographic plate, which then becomes a hologram. When laser light is transmitted through the hologram, one can see a three dimensional virtual image of the object.
