Source: Yong P. Chen, PhD, Department of Physics & Astronomy, College of Science, Purdue University, West Lafayette, IN

Interference and diffraction are characteristic phenomena of waves, ranging from water waves to electromagnetic waves such as light. Interference refers to the phenomenon of when two waves of the same kind overlap to give an alternating spatial variation of large and small wave amplitude. Diffraction refers to the phenomenon of when a wave passes through an aperture or goes around an object, different parts of the wave can interfere and also give rise to a spatial alternation of large and small amplitude.

This experiment will demonstrate the wave nature of the light by observing diffraction and interference of a laser light passing through a single slit and double slits, respectively. The slits are simply cut using razor blades in an aluminum foil and the characteristic diffraction and interference patterns manifest as patterns of alternating light and dark fringes on a screen placed after the foil, when the light is shone through the slit(s) on the foil. Historically, the observation of diffraction and interference of light played important roles in establishing that light is an electromagnetic wave.