Light shaping diffusers are optical components that can homogenize the radiance of an input beam into some specific radiance distribution that will depend on the type of application sought, by effectively averaging out nny irregularity present in the original input beam.
There are two main types of light shaping diffusers which differ from each other in the type of optical phenomena that is being used to achieve the desired beam transformation. Micro lens arrays (MLA), for instance, is a light shaping diffuser that works under the principle of geometrical, or ray, optics. Thus, rays from the beam are brought to a focus whose lateral position will depend on the zone on the MLA that is being illuminated.
The MLA then creates an array of spots at the focal plane that, after some small propagating distance, start to overlap with each other and a new beam envelope is created. Now, if the input beam has any non-uniformity, this will be absent from the output beam.
This behaviour can be explained entirely using only the laws of geometrical optics. As such, the chromatic dispersion, though finite, is considered to be small and manageable.
The other type of light shaping diffusers are those shaping elements that work by the principles of wave optics, which give rise to diffraction effects. Therefore, this other type of light shaping diffusers are known as Diffractive Optical elements or more specifically – Diffractive Diffusers. Thus, in a diffractive optical element, instead of modelling the light as a bundle of rays, the light beam is modelled as a wavefront that is modulated by the pixelated structure of the light shaping element.
Then, after the local modulation imparted locally by the pixels, the diffracted beam evolves into the beam shape that was encoded onto the diffractive optical element. This type of light beam shaper is more versatile than its geometrical optics counterpart as the output radiance distribution can be of any shape.
The radiance on the illuminated areas of the beam can also be Flat Top, that is, uniform, or it can have some gradients. Light diffuser shapers based on diffraction can also be used to alter the focal properties of the beam along the optical axis. They can also be used to create vortex beams which in turn can be used to create doughnut-shaped focal spots.
Light beam shaping diffusers based on diffraction will exhibit a greater dependence on the wavelength. For this reason, diffractive optical elements are better fitted to be used in laser based systems. When the beam is polychromatic, a light shaping diffuser based on geometrical optics, such as the micro lens array, is a better option.
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