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

In summary, the conversation discusses the possibility of using principles of diffraction to cause a collimated beam of light to become divergent. While zone plates are typically used for focusing light, the possibility of using diffraction for defocusing or diverging the light is explored. The search is not limited to traditional optics and includes potential solutions at the nanoscale. One suggestion is to design a Fresnel mirror that could focus a parallel beam onto a focal point, causing the light to diverge as it passes through the zone reflectors. However, there are concerns about achieving the necessary phase delay for a diverging beam.
  • #1
jgk5141
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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.
 
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  • #2
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.
 
  • #3
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,
 

1. How does diffraction work?

Diffraction is a phenomenon that occurs when a wave, such as light, encounters an obstacle or slit that is comparable in size to its wavelength. This causes the wave to bend and spread out, creating a pattern of interference and diffraction. In the case of a Fresnel zone plate, the alternating transparent and opaque zones act as slits, causing the light to diffract and form a focused or diverged beam.

2. What are the advantages of using a Fresnel zone plate for diffraction?

One advantage of using a Fresnel zone plate is its compact size. Unlike traditional lenses, which are bulky and heavy, a Fresnel zone plate can be made thin and lightweight, making it ideal for use in compact devices. Additionally, Fresnel zone plates can achieve higher resolutions than traditional lenses, making them useful for applications such as microscopy.

3. Can a Fresnel zone plate be used to focus or diverge any type of light?

Yes, a Fresnel zone plate can be designed to diffract and focus or diverge any type of light, including visible light, infrared, and ultraviolet. The design of the zone plate, specifically the spacing and thickness of the zones, will determine the wavelength of light that it can diffract.

4. Are there any limitations to using a Fresnel zone plate?

One limitation of using a Fresnel zone plate is its sensitivity to alignment. The zones must be precisely aligned with the incident light for optimal diffraction, and any misalignment can result in a decrease in performance. Additionally, the zones must be accurately and precisely fabricated, which can be challenging and expensive.

5. What are some common applications of using a Fresnel zone plate for diffraction?

Fresnel zone plates have a wide range of applications, including microscopy, lithography, and optical communications. They are also used in spectroscopy to separate and analyze different wavelengths of light. Additionally, Fresnel zone plates are used in solar panels to focus sunlight onto a small area, increasing the efficiency of energy conversion.

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