Laser beam split by a diffraction grating. Diffraction grating is an optical element whose properties are periodically modulated in one dimension. Light transmission through a diffraction grating occurs along discrete directions, called diffraction orders. Here two Helium-Neon lasers, red (632.8 nm) and green (543.4 nm), are used to observe the diffraction patterns from a diffraction grating with 50 lines/mm groove density. The spacing between diffraction orders is larger for longer (red) wavelength (top panel) compared to the shorter (green) wavelength (bottom panel).