Interference of Light

When plane waves come in contact with a barrier that is not significantly larger than their wavelength, the waves spread out into spherical waves (figure 1). The effect is to allow waves to spread out in all directions from the edges of the barrier, a phenomenon called diffraction. This spreading enables the waves to “go around corners”. If two or more rays pass through the same point in space at the same time, they interact with each other. Of special interest is the case in which light passes through slits in a barrier. At any point in space beyond the slits, the local oscillation of the electric field (and the magnetic field, too) will be the result of the sum (or superposition) of the waves from each slit. Such interaction is called interference. Interference may be constructive or destructive. In destructive interference, the peak of one wave meets with the trough of another wave (the two waves are said to be 1/2 wavelength out