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Diffractive Beam splitters

2 Mins read

Diffractive beam splitters are window-like optical components that generate multiple beams from a single input beam. The new beams share the same properties as the input beam, only shifted in space, i.e with a different propagation angle, depending on the design of the beam splitter.

Diffractive beam splitters are a type of diffractive optical element and, as such, they work by taking full advantage of the wave nature of a light beam. In some contexts, the extra beams are referred to as diffraction orders. Beam splitters that work on ray optics, on the other hand, are very limited in the number of extra beams they can generate as well as on what direction they can take.  In contrast, a diffractive beam splitter can generate many beams and they can be arranged in any desired geometrical shape. It can be either a regular pattern or it can also be somewhat irregular in the sense that some dots could be purposely missing from the array.

Diffractive beam splitters can be found in a great variety of applications. Their implementation on any optical system is straightforward because their lateral positioning tolerance is very loose. In fact, as with all periodic diffractive optical elements, the desired output radiance is basically insensitive to errors of this type. Furthermore, diffractive beam splitters are insensitive to the input beam size, as long as the beam covers at least 1-2 periods.

One application of a diffractive beam splitter is beam sampling in high power laser processing. In this case, the zeroth order of the diffractive beam splitter follows the normal path of the laser beam whilst a diffraction order or two are used to monitor the beam shape stability and laser energy in an indirect way but with very good accuracy. Another different application is in an aesthetic treatment referred to as skin resurfacing. In this procedure, a laser beam is expanded with a 2D diffractive beam splitter in order not only to cover a greater area but also by allowing the gap in between dots to help in the skin recovery after the treatment is completed.

One further application for diffractive beam splitters and one which is gaining popularity is for structured light in LIDAR applications. In a LIDAR system the scene in front of the instrument is illuminated with a laser. Then, by measuring parameters like time-of-flight, information about the distances involved can be obtained. If the laser beam is first transformed into a multiple beam array, the information conveyed by the beams ensemble can provide more information about the scene.