I Using Diffraction (i.e., Fresnel Zone Plate) to defocus/diverge light

AI Thread Summary
Using diffraction principles, particularly with zone plates, to create a divergent beam from a collimated laser is a complex challenge. Zone plates are typically designed for focusing light, akin to convex lenses, rather than diverging it like concave lenses. The discussion explores the potential of using nanoscale solutions, such as flat optics or metasurfaces, to achieve this effect. A proposed idea involves designing a Fresnel mirror that could potentially create divergence, but concerns arise about the feasibility of achieving the necessary phase delay. Overall, the search for effective methods to defocus or diverge light using diffraction remains open and requires further exploration.
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Is it possible to defocus collimated light using a concept similar to what is found in a zone plate?
I am wondering if it is possible to use principals of diffraction to cause a collimated beam of light (laser) to become divergent. I see that zone plates are most always used for focusing the light from a source, unless they are used in reverse. This is why zone plates are seemingly always compared to convex lenses. However, I have not been able to find anything that uses diffraction for defocusing or diverging the light, which would be comparable to a concave lens. Does anyone know of any examples of what I am looking for?

Note: I am not limiting the scope of my search to geometrical or large scale optics. I am open to looking at nanoscale solutions, such as flat optics, meta surfaces, or transformation optics, as well as any other solutions.
 
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Maybe design a Fresnel mirror which focuses a parallel beam on to a focal point. The light passing between the zone reflectors will then diverge on the same path, as for a concave lens.
 
I have thought about this more and I don't think I am correct. Such a device would have a focal point both sides of the lens. To produce a diverging beam, we need more phase delay at the centre than the edge, and I am not sure how to achieve that. Not sure it is possible,
 
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