Lesson 15 – Diffraction

When a wave such as light encounters a boundary, such as an aperture, an obstacle, or even a particulate of dust, it will bend around that boundary. This is known as diffraction of light. Boundaries are inevitable in optical systems because the optics have to be supported and the apertures limited. The size and shape of the boundary determine the distribution of the diffraction pattern of light on a screen after the boundary, based on the optical path difference of light across the boundary. Often, the boundary is circular, so the resulting diffraction pattern is a bullseye-like Airy disc of light. The size of a focused spot is determined by the wavelength of the light, the effective focal length (EFL) of the optical system, and the clear aperture (CA) of the optical system. Diffraction gratings are optics composed of many finely spaced grooves through which light must travel, and the diffraction of broadband light causes the full rainbow spectrum to disperse if the source is white light.