Beam shapers are optical elements that can transform the radiance distribution of a beam. One typical example is a micro lens array that is often used as a beam homogeniser that effectively smooths out some of the ripples in the input beam. This type of beam shaper is a diffuser that randomizes the phase, thus it will have a strong speckle effect for temporally coherent single mode lasers . To achieve better shaping, there is another type of beam shaper that works following a totally different principle and is the diffractive beam shaper. As the name implies, a diffractive beam shaper is a free-form diffractive surface that works by harnessing the wave nature of light, and can shape the intensity while keeping a smooth phase profile.
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A diffractive beam shaper is much more versatile than other beam shapers. The type of beam transformations that can be encoded into a diffractive beam shaper are wide and vary. The most common beam shaper transformation is to convert a Gaussian radiance profile, which is intrinsic to many laser systems used in industry, to a more suitable radiance distribution that will depend on the application in question. In many cases of interest, the desired beam transformation is a Flat Top distribution that is characterised by a uniform plateau bounded by hard edges. Thus, a diffractive beam shaper can be used to transform the sun bounded shape from a Gaussian beam into a Flat Top.
As mentioned above, there are a myriad of beam transformations that the diffractive beam shaper can accomplish and producing Flat Top Beams is only one of them. There are some other beam transformations of practical interest such as the generation of different geometrical shapes, like different lines or rectangle arrangements. These sort of patterns are used in applications that require structured illumination such as high end microscopy systems or flat panel and solar panel production, a field of much interest with the move to green energy.
A diffractive beam shaper is a diffractive optical element and as such it consists of a surface topographical profile with a height of the order of a micron. To design a diffractive beam shaper the first step is to define the desired radiance distribution considering all aspects like scaling and beam projection distance. Then, considering the radiance of the input beam, which may not always be a Gaussian radiance distribution, the different height value on each area in the profile is calculated using optimization algorithms. The available algorithms may differ among each other but their end result is always measured by propagating the optical field through the optical element using the diffraction integral.
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