Helium-Neon laser beam split by a diffraction grating. Diffraction grating is an optical element whose properties are periodically modulated in one dimension. Transmissive diffraction gratings consist of many thin lines of either absorptive material or thin grooves (indentations) on an otherwise transparent substrate. Light transmission through a diffraction grating occurs along discrete directions, called diffraction orders. Here a Helium-Neon laser beam (633 nm) incident from the right is split into many diffraction orders, with +1 order containing most of the power. Characteristic laser speckle pattern is apparent.