Diffraction gratings are perhaps the simplest type of diffractive optical elements. Diffraction gratings split an incoming beam into other beams thar are referred to as diffraction orders. Each order has a specific angular direction and intensity. The angular direction is not random, but it is determined by the wavelength and the grating period, according to the grating equation. Another interesting aspect is that since the angular direction is directly dependent on the wavelength, a lot of chromatic dispersion is expected and because of this, a diffraction grating has been an integral component for spectroscopic systems from their very beginnings.
Diffraction gratings can be of two sorts which are amplitude and phase gratings. In amplitude gratings the modulation is done by either blocking or passing the light, resulting in loss of 50% of energy. In contrast, phase gratings add a retardation to the wavefront of the beam, as opposed to just blocking some parts of it. In terms of angular direction for the generated beams, there is no difference between the two types. The difference resides in the amount of energy that ends up in the diffraction orders. While transmission gratings lose at least 50% to absorption and another 18% of that to diffractive efficiency, diffractive gratings start with efficiency of 82% for simple binary structures and can reach almost 100% for blazed gratings with multiple phase levels.
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With the advent of advanced design methods for diffractive optical elements, diffraction gratings have evolved into more complicated structures. Nowadays, a diffraction grating can be designed to split an input beam to many beams that have the same intensity, each beam representing a different diffractive order. A diffraction grating that splits the beam into many beams with the same intensity is also referred to as a Dammann grating, or a diffractive beam splitter
A diffraction grating that splits the beam into many other beams can be used in many laser systems. For instance, it can be used in laser drilling of filters to create multiple precise holes. It can also be used for aesthetic laser skin treatments, where multiple orders are used to stimulate the skin to regenerate by creating controlled micro-burns at precise separations.
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