# Controlling light diffraction angle with a holographic "lens"

• Mike Gaffer
In summary, controlling light diffraction angle can be achieved through the use of a holographic "lens." This technology utilizes holography to manipulate the direction and intensity of light, allowing for precise control over the angle at which the light is diffracted. This has potential applications in various fields such as telecommunications, imaging, and data storage. By harnessing the power of holographic lenses, researchers and engineers can design and create more efficient and advanced devices for manipulating light.
Mike Gaffer
I'm a physics student, and working on a class project that requires coming up with a method to control
the exit angle (diffraction angle) of a monochromatic light source.

For example, taking a laser (monochromatic, coherent light source), spreading the beam, and directing the light at a piece of holographic film. Then, depending on how the original "hologram" or diffraction grating was recorded or encoded, determining the direction of the transmitted light. Basically, I'm trying to create a "holographic lens" of sorts.

Is this possible? and what resources would you recommend in figuring out how to expose or record the diffraction pattern?

Thanks for any info in advance!

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I guess the question is, how could I make a diffractive optical element (DOE), and is it possible to do this with holographic film?

Mike Gaffer said:
I guess the question is, how could I make a diffractive optical element (DOE), and is it possible to do this with holographic film?

I suspect you could do this with a spatial light modulator.

Mike Gaffer
When you say 'control', do you mean variable control or just deflect by a given angle?
Your two diagrams seem to suggest that a diffraction grating could do the job. You can make a basic diffraction grating photographically using Young's slits (just one half of the pattern will have equal spaced maxima). You can work out the slit spacing for a given grating pitch and the slit spacing will need to be wider than for a normal Young's demo because the grating needs to be finer than you can easily see.
I don't know the present state of the art with home-made holography but I do know that the optics and the supports need to be held pretty steady and the film needs to be high res. (Those comments apply whatever your final solution is.)
PS the slits will need to be very narrow (as near omnidirectional patterns as possible) if you want the grating to have many maxima of 'equal' amplitude.

Mike Gaffer
arydberg said:
Ah yes - the Zone Plate works like a convex lens. I was well impressed with that when I first came across it. (But I had forgotten the name so I couldn't look it up )

How rapidly do you need to steer the beam ? Plane or volume ??

D'uh, how about a mirror plus $10 servo-motor per DOF ? Provided the angle is modest, internal reflection via an optical-grade prism may be easier than keeping a small, front-surface mirror clean. You'll find ample Arduino etc source-code on-line. Trouble-shoot / demonstrate your rig with a budget 'servo tester'... Don't laugh-- One of my friends built such a 'micro-disco FX' as a cat-toy... sophiecentaur said: Ah yes - the Zone Plate works like a convex lens. I was well impressed with that when I first came across it. (But I had forgotten the name so I couldn't look it up ) But I think the zone plate loses half the power. Andy Resnick said: I suspect you could do this with a spatial light modulator. https://www.meadowlark.com/spatial_light_modulators.php I'm not familiar with spatial light modulators, other than having seen the term before... is this the type of module that is being used to generate true holograms in real time with massive amounts of computer data being fed into them? Would you know any place to start on _how_ I would use one? sophiecentaur said: When you say 'control', do you mean variable control or just deflect by a given angle? Your two diagrams seem to suggest that a diffraction grating could do the job. You can make a basic diffraction grating photographically using Young's slits (just one half of the pattern will have equal spaced maxima). You can work out the slit spacing for a given grating pitch and the slit spacing will need to be wider than for a normal Young's demo because the grating needs to be finer than you can easily see. I don't know the present state of the art with home-made holography but I do know that the optics and the supports need to be held pretty steady and the film needs to be high res. (Those comments apply whatever your final solution is.) PS the slits will need to be very narrow (as near omnidirectional patterns as possible) if you want the grating to have many maxima of 'equal' amplitude. By _control_, I was looking at dividing an optical element, whether it be holographic film, or something else, into a grid; having each segment of the grid diffract a beam that is directed at it, at a unique output angle, and be able to calculate the output angle predictably. Then, be able to make this optical element so that I can have for example, square grid on the element (col 1, row 1) redirect light at 15 degrees, col 1, row 2 at 30degrees, col 2, row 1 at -10 degrees, etc... almost like a complex arrangement of little mirrors. tech99 said: But I think the zone plate loses half the power. Very interesting! Will look into this further. Nik_2213 said: How rapidly do you need to steer the beam ? Plane or volume ?? D'uh, how about a mirror plus$10 servo-motor per DOF ? Provided the angle is modest, internal reflection via an optical-grade prism may be easier than keeping a small, front-surface mirror clean.

You'll find ample Arduino etc source-code on-line. Trouble-shoot / demonstrate your rig with a budget 'servo tester'...

Don't laugh-- One of my friends built such a 'micro-disco FX' as a cat-toy...
The angle, once determined, won't need to change. But I need to have potentially hundreds of different angle "quadrants" or areas on the element that would each need to be "steered" uniquely. Also weight, power, and potentially production type quantities would make the motor not applicable for this application - but otherwise good idea! Thanks

sophiecentaur said:
When you say 'control', do you mean variable control or just deflect by a given angle?
Your two diagrams seem to suggest that a diffraction grating could do the job. You can make a basic diffraction grating photographically using Young's slits (just one half of the pattern will have equal spaced maxima). You can work out the slit spacing for a given grating pitch and the slit spacing will need to be wider than for a normal Young's demo because the grating needs to be finer than you can easily see.
I don't know the present state of the art with home-made holography but I do know that the optics and the supports need to be held pretty steady and the film needs to be high res. (Those comments apply whatever your final solution is.)
PS the slits will need to be very narrow (as near omnidirectional patterns as possible) if you want the grating to have many maxima of 'equal' amplitude.
By "control" I mean, divide a piece of film into a grid of for example, 100 columns, and 100 rows, and have each square of the grid cause a beam impacting it to be "steered" at a different output angle... almost like a piece of engineered bumpy glass.

Mike Gaffer said:
I'm not familiar with spatial light modulators, other than having seen the term before... is this the type of module that is being used to generate true holograms in real time with massive amounts of computer data being fed into them? Would you know any place to start on _how_ I would use one?

I don't know your level of expertise, but:

https://www.hamamatsu.com/resources/pdf/ssd/e12_handbook_lcos_slm.pdf
http://spie.org/Publications/Book/2281295?SSO=1
https://arxiv.org/pdf/1708.02485.pdf

Mike Gaffer
Mike Gaffer said:
By "control" I mean, divide a piece of film into a grid of for example, 100 columns, and 100 rows, and have each square of the grid cause a beam impacting it to be "steered" at a different output angle... almost like a piece of engineered bumpy glass.
That sounds more and more like a diffraction grating. It seems that you don't envisage actually steering a beam (?). A diffraction grating will give beams at different angles at the same time, according to a simple rule. Your idea of using a hologram would be fairly straightforward. If you use multiple (split) beams of laser light - at the angles you will want, finally, they will interfere at the surface of your film and produce a hologram. This hologram will produce beams at the same angles when illuminated with a plane wave. It's actually a simpler thing to visualise (IMO) than what happens when a hologram is produced by shining laser light at a complicated object.
If you want to steer the beam, the methods suggested by @Andy Resnick are cool - but several stages in advance of the simple system you seem to be suggesting.

This idea is not the best because the hologram can occupy the whole of the film slide and each part of it will contribute to each output beam. That's how holograms work and the beams would be sharper because the 'aperture' would be wider and I think the beams would be brighter.

## 1. How does a holographic lens control light diffraction angle?

A holographic lens is a type of lens that uses holography, a technique that records the interference pattern of light waves, to manipulate and control the diffraction angle of light. The holographic lens is made up of a series of microscopic grooves or patterns that are etched onto the surface of a material, typically glass or plastic. These patterns interact with the incoming light waves, causing them to diffract and bend in a specific way, thus controlling the angle at which the light is dispersed.

## 2. What are the advantages of using a holographic lens for controlling light diffraction angle?

One of the main advantages of using a holographic lens is its ability to precisely control the diffraction angle of light. This allows for more accurate and efficient focusing of light, making it useful in a variety of applications such as microscopy, laser technology, and holographic displays. Additionally, holographic lenses are lightweight, compact, and can be mass-produced at a low cost, making them a practical choice for many industries.

## 3. Can a holographic lens be used to control the diffraction angle of all types of light?

Yes, holographic lenses can be designed to work with a wide range of light wavelengths, including visible light, ultraviolet light, and infrared light. The specific design and materials used for the holographic lens will determine its effectiveness for a particular type of light. For example, a holographic lens made for visible light may not work as well for infrared light.

## 4. How does the diffraction angle of light affect image quality?

The diffraction angle of light plays a crucial role in image quality. When light passes through a lens with a controlled diffraction angle, it can produce a sharper and clearer image. On the other hand, if the diffraction angle is not controlled, the light can scatter and cause distortion, resulting in a lower-quality image. This is why holographic lenses are often used in imaging systems to improve image quality.

## 5. Are there any limitations to using a holographic lens for controlling light diffraction angle?

While holographic lenses have many advantages, they also have some limitations. One limitation is that the diffraction angle can only be controlled within a certain range, depending on the design and materials used for the lens. Additionally, holographic lenses may be more sensitive to environmental factors such as temperature and humidity, which can affect their performance. However, with advancements in technology, these limitations are continuously being addressed and improved upon.

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