Diffractive beam shaper

Diffractive beam shaper

Beam shaper is a general term to refer to optical elements that can alter the radiance of an input beam. For example, a much sought-after transformation is to convert a Gaussian beam radiance into a Flat Top radiance distribution. In this operation, the introduction of the beam shaper can boost the performance of the laser system by eliminating the Gaussian radiance, which is in fact inherent to many laser systems. A Flat Top radiance profile of the beam results in a more efficient system.

There are two types of beam shapers that differ in their principle of operation. On the one hand, there are diffuser shapers and on the other hand, we have analytical beam shapers. Which type of beam shaper is used will depend on the characteristics of the input beam. For instance, if the beam is incoherent, multi-mode, and perhaps even polychromatic, then the best choice is to use a diffuser-type beam shaper.  Diffractive beam shaping diffusers can produce sharp edges and any desired profile, but internal uniformity will depend on the input beam coherence, as the diffuser scrambles the phase. Thus, the more incoherent the beam, the smoother the intensity.  For cases where the beam is monochromatic, coherent, and single-mode the best option by far is the analytic beam shaper., which is often a diffractive beam shaper.  These Shapers enable the exact transformation to very small shapes (a few diffraction limits), with sharp edges, excellent uniformity, and very high efficiency.

A diffractive beam shaper is a diffractive optical element and as such it consists of an array of small modulating elements, that can be likened to pixels on an image, that impart a local phase delay to the incoming wavefront of the input beam. The effect that all these local phase modulations have on the overall wavefront is related to the optical transformation that is needed from the diffractive beam shaper. As the new beam distribution appears at a very large distance away from the diffractive beam shaper, typically an external lens is used to create the desired shape at the focal plane.

With an analytical diffractive beam shaper the desired transformation is encoded into the element’s pixels in a very particular way. But the important aspect to consider is that almost any transformation can be encoded. This means that the output beam can be of any geometrical shape or it can even consist of separated zones, such as parallel lines. The radiance on the lit areas can be a Flat Top or any other distribution.

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