What is the term for the spreading of light waves as they pass through a narrow opening?

The spreading of light waves as they pass through a narrow opening is known as diffraction. This phenomenon occurs when waves encounter an obstacle or a slit that is comparable in size to their wavelength. As the light waves pass through the opening, they bend around the edges and spread out, creating patterns of light and dark fringes. This behavior illustrates the wave nature of light, showcasing how it can change direction and form new patterns rather than simply traveling in straight lines.

In diffraction, the extent of the spreading and the resulting pattern depends on both the wavelength of the light and the dimensions of the opening. This principle has various applications in optics, such as in the design of diffraction gratings used in spectrometers to analyze light.