Improvement on my project

Dichromated Gelatin.
Zeta
Posts: 42
Joined: Wed Jan 10, 2018 9:30 am

Re: Improvement on my project

Post by Zeta » Mon May 07, 2018 2:15 am

Is first surface mirror and one way mirror the same?

pluto
Posts: 94
Joined: Fri Feb 05, 2016 2:06 am

Re: Improvement on my project

Post by pluto » Mon May 07, 2018 1:45 pm

Zeta wrote:Is first surface mirror and one way mirror the same?
Not sure about that.

Edmund Optics tends to have first surface mirrors for quite cheap:

https://www.edmundoptics.com/optics/opt ... e-mirrors/

Take a look at their clearance items as well. Ebay might be a better option if you're not in Canada or USA. Only bad thing is the shipping and duties when ordering from outside USA.

lobaz
Posts: 234
Joined: Mon Jan 12, 2015 6:08 am
Location: Pilsen, Czech Republic

Re: Improvement on my project

Post by lobaz » Mon May 07, 2018 5:47 pm

Zeta wrote:Is first surface mirror and one way mirror the same?
No. A common mirror (such as the one from a bathroom) is a piece of glass that has silver coating on its back side. If you are looking to the mirror and scratch the surface, you actually scratch a glass, not the silver layer. If you put a finger close to the mirror, you see its strong reflection from the silver back side and a weak reflection from the front glass surface.

A first surface mirror is coated on the front surface. It can be easily damaged, it is better not to touch it at all. But for optics, it is much better than a common mirror. Here is the reason.

If you illuminate a front surface mirror with a laser, you get a perfect reflection.

If you illuminate a common mirror with a laser, you get two reflections, one from the back silver surface and one (weak) wrom the first one. These reflections interfere and create a banded structure. These bands are very disturbing in dispay holography.

I got a nice (and large) front surface mirror from suppliers for DYI projectors. You can also fined ones in old overhead projectors, scanners and maybe other electro-optical devices. You can also use platters from an old hard disk. In short: anything perfectly flat with one reflecting surface.

---

A one way mirror is something completely different. It is a piece of glass coated with a thin layer that is partially transparent and partially reflects light, e.g. in ratio 50:50. If you look at such glass and there is darkness behind it, you see a perfect mirror reflection. If, on the other hand, the environment behind the glass is much brighter than the environment in front of it, you can see throuh. It is just a matter of fact if transmitted light is stronger or weaker than reflected light. A common architectural application is a one-way mirror between a well illuminated stage and a dim control room. Those inside the control room can see the stage, but not vice versa.

In fact, a one way mirror is called a beam splitter by opticians. However, common one way mirrors can be far from quality required by precision beam splitters.

Hope this helps.

Petr

Zeta
Posts: 42
Joined: Wed Jan 10, 2018 9:30 am

Re: Improvement on my project

Post by Zeta » Tue May 08, 2018 10:34 am

Update new problem

Nothing on the plate

Just shiny yellow and red and little purple
64F76397-4CB9-4230-ABA4-D19E8A70E32F.jpeg
64F76397-4CB9-4230-ABA4-D19E8A70E32F.jpeg (107.79 KiB) Viewed 3646 times
No more mirror
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Still no
003BA765-7A69-4D71-8234-0864AD4247C1.jpeg
I overdry and burn the middle of the plate
003BA765-7A69-4D71-8234-0864AD4247C1.jpeg (108.15 KiB) Viewed 3646 times
More visible in video
https://youtu.be/YxbP0xf2Mck


I feel like my improvement is going backwards :(

lobaz
Posts: 234
Joined: Mon Jan 12, 2015 6:08 am
Location: Pilsen, Czech Republic

Re: Improvement on my project

Post by lobaz » Tue May 08, 2018 1:20 pm

Zeta wrote:Nothing on the plate
The most likely reason is bad stability. I would proceed in following steps:

1. Repeat some setup that was OK. Probably small plate, simple object (coins) in contact with the plate, short exposure time.

If you succeed, proceed step by step:

2. Small plate, short exposure time, simple object (coins) that is not in direct contact with the plate.

3. Small plate, short exposure time, "advanced object" that is not in direct contact with the plate.

4. Small plate, long exposure time, "advanced object" that is not in direct contact with the plate.
You can move the laser farther from the hologram to make the exposure time longer, use a ND filter or so.

5. Large plate, long exposure time, "advanced object" that is not in direct contact with the plate.

Debugging what went wrong is a painful process. Start with something that works and proceed slowly.

Zeta
Posts: 42
Joined: Wed Jan 10, 2018 9:30 am

Re: Improvement on my project

Post by Zeta » Thu May 10, 2018 2:34 am

It is my plate holder that not stable, so now I just put the plate on top of the object

This one using front surface mirror
No strip line on my plate
But not really bright and sharp but can see a detail in deeper part
1hr 30min exp 30 min dark

https://youtu.be/VoHISvw2W_s

Thin one use normall mirror
Sharper but only part that close to the plate deeper part is super dim
1hr 30min exp 17hr dark

https://youtu.be/UbPd8euEoPo
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Object is nikonos
96038AD6-E09D-49EB-8016-1783435AEF0E.jpeg
96038AD6-E09D-49EB-8016-1783435AEF0E.jpeg (24.83 KiB) Viewed 3625 times

pluto
Posts: 94
Joined: Fri Feb 05, 2016 2:06 am

Re: Improvement on my project

Post by pluto » Thu May 10, 2018 7:46 pm

90 minute exposure without vibration is going to be tough... you can see how the lens part is clearer because it's in good contact with the glass, and thus more stable.

Definitely keep going with the first surface mirror. I still recommend making smaller holograms... early on you want to create as many holograms as possible (while taking notes) and get a good feel for how different variables affect the result.

I'm maybe 100 exposures in, and I'm finally now starting to get a hang of it... but I'm probably a slow learner :)

Zeta
Posts: 42
Joined: Wed Jan 10, 2018 9:30 am

Re: Improvement on my project

Post by Zeta » Fri May 11, 2018 11:43 am

I still using normal mirror because I have to make a set of work and I have done 5 good plate with normal mirror if I change now my prof. will question me about the different in this set of work.

This one is sharp but still dim
It is a black plastic camera
2hr. Exp 17hr. Dark
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8F6708FB-E49D-401D-AAEB-AF137F3F2565.jpeg (1.88 MiB) Viewed 3559 times
https://youtu.be/M9_vLsugmfE

The problem of my last camera is everything is black and not shiny (black metal and black leather) so it doesn’t reflect laser back to the plate but the little shiny thing on left and right is bright and sharp

pluto
Posts: 94
Joined: Fri Feb 05, 2016 2:06 am

Re: Improvement on my project

Post by pluto » Fri May 11, 2018 5:02 pm

The black plastic isn't ideal for holograms. A silver/metal camera would probably show up a lot better.

Also you'll always have those lines unless you use a first-surface mirror. Not sure why your professor would mind you using better equipment, but I highly recommend it. Having two reflections from your mirror could be causing other issues as well, as I imagine they would form a secondary interference pattern?

Play with the exposure time as well, look at this graph of exposure vs diffraction efficiency:

Image

The diffraction efficiency does go back up when you expose 3-4 times longer than required, but you start getting burn-in. I believe DCG is intentionally exposed at these sorts of lengths to produce HOEs, but it's not ideal for display holography.

What is the area of your expanded beam? And what is the power of your laser?
Last edited by pluto on Fri May 18, 2018 6:28 pm, edited 1 time in total.

Zeta
Posts: 42
Joined: Wed Jan 10, 2018 9:30 am

Re: Improvement on my project

Post by Zeta » Sat May 12, 2018 2:11 am

My expanded beam diameter is around 14” a size of A4 paper, laser is 50mw

Smaller test but same setup
my casio watch
30min exp 30min dark
I did not put the tape around the edge
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https://youtu.be/souMItpUjZM

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