Diffraction

Diffraction, deviation and spreading of waves (such as electromagnetic radiation, sound or water waves) from a straight line, occurring when waves encounter an obstacle. Diffraction effects place the limit on the resolving power of optical instruments, radio telescopes, and the like. In a spectrograph, light passed through or reflected from a diffraction grating, a series of very accurately ruled slits or narrow parallel mirrors, produces a series of spectra by the interference of light from the different slits or mirrors.