Holographic Optical Element (HOE) of simple reflection mirror

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moonlight
Posts: 4
Joined: Sat Nov 07, 2020 3:35 pm

Holographic Optical Element (HOE) of simple reflection mirror

Post by moonlight »

Hi,
I'm trying to get a holographic setup to simulate a reflection HOE for an actual reflection mirror (not an image of a mirror) an actual flat mirror specs.
I'm using 532nm (green) laser as test & Incident beam should be 60degree from normal of HOE and the reflected beam is 0degree to normal as shown in target diagram
Target
Target
Target.jpg (155.66 KiB) Viewed 6193 times
My questions are:
-Which of the attached setup (Setup1
Setup1
Setup1
Setup_1.jpg (202.37 KiB) Viewed 6193 times
or Setup2
Setup2
Setup2
Setup_2.jpg (192.26 KiB) Viewed 6193 times
) would be correct to get the HOE for the mirror
-If none of my setup works to simulate the mirror what would be the correct setup, if possible please show a diagram of the setup
-Is there a specific formula that relates the Incident beam with the reflected beam using HOE grating, in other words if the incident beam angle is 60degree from normal how to reflect Reflection beam at 0degree from normal using 632nm wavelength.
BobH
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Location: Mesa, AZ

Re: Holographic Optical Element (HOE) of simple reflection mirror

Post by BobH »

System #2 if you don't have a stable table. System #1 if you do, and want best results. Both will work fine. Others may say system #2 gives best results.
Din
Posts: 402
Joined: Thu Mar 12, 2015 4:47 pm

Re: Holographic Optical Element (HOE) of simple reflection mirror

Post by Din »

Setup #1. You have more control of the beam width because you can put two beam expanders at any point after the beamsplitter. In setup #2, you don't have this flexibility, whatever beam expansion you use, you have no choice over the beam width for your object beam, this is decided by the expander in the reference beam. Setup #2 will probably result in vignetting, among other aberrations. You'll also get noise. I'm assuming you have enough coherence for #1.
moonlight wrote: Sat Nov 07, 2020 3:51 pm Is there a specific formula that relates the Incident beam with the reflected beam using HOE grating, in other words if the incident beam angle is 60degree from normal how to reflect Reflection beam at 0degree from normal using 632nm wavelength.
Not sure what your question is. Are you asking if there is a formula for the Bragg slant, and the Bragg vector? Yes, there is. At the centre, the Bragg spacing is Λ = λ/cos(60), and the direction of the K vector, K = 30 deg to plate normal, ie K = Λ(cos(30)i + sin(30)j). See diagram below. At the edges, it depends on the beam expansion. Bear in mind, this is not including variation of your reflection angle and loss of efficiency due to material expansion. To determine that, you need the Bragg dephasing parameter β.
Bragg062.jpg
Bragg062.jpg (244.47 KiB) Viewed 6177 times
moonlight
Posts: 4
Joined: Sat Nov 07, 2020 3:35 pm

Re: Holographic Optical Element (HOE) of simple reflection mirror

Post by moonlight »

Hi Din,
So from my understanding Setup1 give more control on the beam width because you mentioned we can add beam expander at any point, does this means we have more control on the reference beam ratio to the object beam ratio which have to be 3:1 or 4:1 for holography ?

-Yes I was asking about the Bragg Slant & Victor Bragg, thanks for sharing the formula that's almost the same as the diffraction grating design formula, so I do understand 2 things:
1) Bragg vector angel K=30degree to normal to reflect Incident light from 60degree to 0 degree to normal
2) Bragg spacing formula Λ = λ/cos(60)
knowing that so film manufacturer facilities would be designing Bragg spacing to reflect specific wavelength ex:532nm...etc but how to get films with Bragg vector angel K=30degree to work in my application, do I need to customise that film to get the exact Bragg angel? who can customise it?
Din
Posts: 402
Joined: Thu Mar 12, 2015 4:47 pm

Re: Holographic Optical Element (HOE) of simple reflection mirror

Post by Din »

moonlight wrote: Mon Nov 09, 2020 6:32 pm Hi Din,
So from my understanding Setup1 give more control on the beam width because you mentioned we can add beam expander at any point, does this means we have more control on the reference beam ratio to the object beam ratio which have to be 3:1 or 4:1 for holography ?
You need two beam expanders. A beam expander takes in the laser beam and expands it to cover the medium. In your setup #1, you have two independent beams coming from the beamsplitter, so you can put a beam expander in each arm. In your setup #2, the reference and object beam are the same beam deflected by the mirror. You have no independent control of the reference and object beams.
moonlight wrote: Mon Nov 09, 2020 6:32 pm-Yes I was asking about the Bragg Slant & Victor Bragg, thanks for sharing the formula that's almost the same as the diffraction grating design formula, so I do understand 2 things:
1) Bragg vector angel K=30degree to normal to reflect Incident light from 60degree to 0 degree to normal
2) Bragg spacing formula Λ = λ/cos(60)
knowing that so film manufacturer facilities would be designing Bragg spacing to reflect specific wavelength ex:532nm...etc but how to get films with Bragg vector angel K=30degree to work in my application, do I need to customise that film to get the exact Bragg angel? who can customise it?
The Bragg vector and spacing are determined from the recording geometry. I was using your geometry of 0 degrees and 60 degrees. other geometries will give different vectors and spacing. The film is irrelevant so far as the Bragg conditions are concerned, so long as the film can record the spatial frequencies. But, the film determines the possible efficiencies.
moonlight
Posts: 4
Joined: Sat Nov 07, 2020 3:35 pm

Re: Holographic Optical Element (HOE) of simple reflection mirror

Post by moonlight »

I used setup2 with 532nm coherent laser and I removed the lens from the laser module to get the beam expanded and I got some pretty good results as shown below
Setup2.JPG
Setup2.JPG (93.13 KiB) Viewed 6133 times
I'm using a regular white flash light for image construction and the image looks good with high detailed resolution

However when I replaced the object with a flat mirror same as we discussed before to record HOE for flat mirror specs, I run into 2 issues:
1) I used a regular off shelf mirror (not optical grade) and the reflection shows some strips on the film as shown in the image below, I tested the same mirror directly with the laser on white wall and it looks like the mirror is not able to reflect all incident light from the laser diode and I can still see the strips reflected on the wall, using the laser directly on the wall doesn't give the strips at all, do I need to use a special type of reflecting mirror with the laser to remove those strips? If so what would be the best mirror type for the application?
Light_strips1.PNG
Light_strips1.PNG (293.75 KiB) Viewed 6133 times
2) I tested the output holography with strips using an image directly from my cell phone and the image looks blurry, but when I move the phone very close to the film, the image got adjusted better but still blurry, it looks like it's acting like a lens or mirror with a focal lens so when I move the image away from the film it's very blurry and gradually when I move it towards the film (using same reference beam angel) image quality improve but still blurry not acting like a clear flat mirror reflection, any idea or hints to fix the blurry issue?
jrburns47
Posts: 165
Joined: Mon Sep 14, 2015 2:48 pm
Location: Oyster Bay, NY

Re: Holographic Optical Element (HOE) of simple reflection mirror

Post by jrburns47 »

It makes a difference if a cell phone camera is horizontal or vertical to a hologram image sometimes, at least for an iPhone XS Max.
holomaker
Posts: 772
Joined: Wed Jan 07, 2015 8:01 am

Re: Holographic Optical Element (HOE) of simple reflection mirror

Post by holomaker »

Don’t shoot so close to hologram, adjust light intensity
Move light source further away or use a dimmer to adjust
amount of light. Record and then enlarge...
lobaz
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Joined: Mon Jan 12, 2015 6:08 am
Location: Pilsen, Czech Republic

Re: Holographic Optical Element (HOE) of simple reflection mirror

Post by lobaz »

The strips you see are most likely from interference between reflection on the first surface of the mirror (glass) and on the second surface (silver or Al). You need a first surface mirror, i.e., the there in no cover glass on the silver surface.
lobaz
Posts: 280
Joined: Mon Jan 12, 2015 6:08 am
Location: Pilsen, Czech Republic

Re: Holographic Optical Element (HOE) of simple reflection mirror

Post by lobaz »

Dinesh, did you take into account index of refraction of the emulsion in your back-of-the-envelope calculation? I guess the Bragg planes would not be at the angle 30 deg.
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