Diffraction and Interference

What is the interference of light?

We’ve explored wave interference before in the Waves chapter. The key to the interference of light is that the two (or more) waves interfering must have the same wavelength and phase. While interference can be seen with ordinary light, interference is most easily seen using laser light. If light from a laser passes through two slits that are a small distance apart the diffraction patterns from the two slits will overlap. When they do a pattern of light and dark bands will be seen. The bright bands are where waves from the two slits are constructively interfering. The distance the light has traveled from the two slits will be equal or they will differ by an integer number of wavelengths. The dark bands occur when the waves destructively interfere. In this case the difference in distance light from the two slits will have traveled will be an odd number of half wavelengths. That is, one-half, three-halves, five-halves, etc. Light can also interfere if it is reflected off two closely spaced interfaces, like the two surfaces of a soap bubble or oil film.


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