When you’re talking about optics, things are often happening on a nanometer scale. This means that even the slightest amount of vibration can spoil delicate work. [The Thought Emporium] is working on a long-scale project to produce chocolate holograms, and needed a stable surface to set up some optical components. Thus, he decided to build a magnetically levitated laser table.
The build starts with a series of eight machined delrin bushings, each mounting a strong neodymium ring magnet. Four are placed on the base, with a thin steel rod protruding upwards. The other four bushings are then placed such that the poles of the magnets are opposite one another, causing them to levitate. An acrylic plate is then lowered on top, being supported by the levitating magnets.
It’s a very simple way to create a magnetically levitated table, and in a basic interferometry test, appears to do a decent job of isolating the table from vibrations. We also wonder if there’s scope for further improvement through the use of some kind of eddy current damper. It should make an excellent platform for further experiments, and we look forward to seeing some chocolate holograms in the near future.
It turns out that [The Thought Emporium] was inspired by an earlier chocolate optics project. Video after the break.
Unless it’s active magnetic levitation, wouldn’t cheaper springs give a similar isolation effect? Even better – use high mass in the table for dampening, and compliant mountings for isolation.
Aren’t the magnets just acting as springs? It seems to me, that with no damping, if the base magnets vibrate, the vibration will be transferred to the platform. I would think the normal way to do this would be to stand a massive optical table on spikes that contact a concrete floor.
You can put copper tubes enclosing the magnets. The eddy current caused by movements in magnet would help to damp their motion.
The traditional stack is a steel and granite table riding on air coasters, preferably on a concrete floor, yes. The air provides some isolation, but it isn’t what damps out the vibration. That’s all down to mass, and this just project just doesn’t have any.
permanent magnets in this configuration will fail sooner rather than later.
Where do you get this idea from. My understanding is that permanent magnets will last a long time in any configuration, on the order of many hundreds of years. https://www.sciencefocus.com/science/do-magnets-wear-out/
i’ve demagnetized magnets by epoxying them down in a repelling configuration. you can repeat the experiment for about $1, or google for something along the lines of “what happens when you force the repelling ends of two magnets together”.
Here is a link discussing this https://www.quora.com/Will-forcing-two-magnets-together-along-repeling-poles-weaken-the-magnets-after-a-while
Back in the day of HeNe lasers people used sand boxes on mildly inflated inner tubes from cars. The optics were mounted on pieces of PVC pipe you could stick in the sand where you wanted. I thought sand and optics was a bad idea. In the lab I worked in we got rid of a big old load press. I had dibs on the bed after we got it apart. The bed was about 3×4 feet by 4 or so inches thick steel. It took 6 of us to drag it down to a storage room. I never did round up enough people to get it into my truck, which is just as well because it would have taken that many people to get it back out of my truck and my plan was to set up shop in the basement and I am not sure the wooden stairs would have held the required number of people and the gigantic piece of steel. The plan was to use inner tubes and PVC glued to those doughnut shaped ceramic magnets that Radio Shack used to sell. I have not been in my old lab, it has changed hands quite a few times now, in over 30 years, but I wonder if that hunk of steel is still in the storage room.
As far as the magnets and acrylic goes, it looks pretty. I am not sure it has enough mass. If it fails as an optical table it might make a cool piece to keep an audio turntable on.
My HAD optics project did laser interferometry on a conference table – using laser cut acrylic holders simply placed on the table.
If you bang on the table the interference fringes will scatter, but in general simply not touching the table is sufficient. No special dampening needed.
This probably won’t be true for white light holograms, but I doubt that’s what they’re doing.
In other words, don’t worry too much about vibration or dampening when making holograms – simpler is better.
The problem is not only damping vibrations, but also the frequency and power (intensity) of the vibrations. Optical benches are often mounted on very heavy objects, like granite slabs. Unfortunately, even these will transmit some specific frequencies. I used to make holograms, and vibration damping is the major concern. Some materials do better than others at damping. Sorbothane covers a very wide range, but even that will transit some. Regarding magnetic levitation, and the inner tubes (yes, I used large tubes made for tractor tires), even air will transmit vibrations. That is how a loudspeaker gets the sound to your ears. I found that the best results were usually to use a combination of different materials, each of which dampened different frequencies. Make sure that Sorbothane is in the stack of absorbers.
I like how no one seems confused as to what a chocolate hologram is? That makes absolutely no sense to me!
Surely someone can explain this trivial insanity?
I had the same question, and was disappointed to find no answers in the article.
I’m guessing it’s something like this:
https://www.npr.org/sections/thesalt/2014/06/14/321816570/holographic-chocolates-look-as-beautiful-as-they-taste
Holograms don’t use chemicals to display an image – they use nanostructures that reflect or refract light in such a way that it interferes with itself to produce a desired light field. As such, anything which can hold the appropriate structures cast onto it’s surface can display a hologram – chocolate happens to be one of them.
The second link in the article. That youtuber was casting chocolate (and other things) on diffraction grating plastic, so you end up with that iridescent sheen even though we know that chocolate’s surface is just brown.
Cool idea but it seems to me that of the three axes vibration can couple this only solves vibrations in one. Maybe instead of mounting it on a surface he could suspend it from wires.
Float the lexan top portion on an air hockey table
This is kinda puzzling. The force between dipoles is proportional to the square, unlike springs, which are linear. The magnet system is much harder to model. And “damping” is the conversion of kinetic energy into heat, like in a shock absorber, but the magnets are conservative (mostly).
In some cases, large moment of inertia helps by shaping the frequency response. In other cases, like active control, less mass makes it easier.
I don’t see any reasoning behind this except maybe; tires and a sandbox is good, so magnets are better? DIY optical tables are a great topic, but I’m missing something.