Diffraction of Light: Grimaldi and Huygens

In 1665 Italian scientist Francesco Maria Grimaldi observed that the edges of shadows are not

perfectly sharp. He introduced a narrow beam of light into a dark room and held a rod in

front of the light such that it cast a shadow on a white surface. The shadow cast

by the rod was wider than the shadow should have been if light traveled in a straight line

past the edges of the rod. Grimaldi also noted that the shadow was bordered by

colored bands. He determined that both of these observations could be explained if light bent slightly.

He called the bending of light as it passes the edge of a barrier diffraction. Huygens' principle

In 1678 Dutch scientist Christian Huygens used a wave model to explain diffraction. According to Huygens'