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

[jgk5141]

TL;DR Summary

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.

 

[tech99]

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.

 

[tech99]

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,