> The two beams (split in the beam splitter—the little rectangle with a diagonal in the center) add or subtract constructively at the output, which yields fringes that are visible to the naked eye. These fringes will move as light from one of the arms of the interferometer takes a longer or shorter path<p>This explanation is bit incomplete. If you align the interferometer perfectly then it should not have any fringes, the fringes indicate that there is some angle between the light beams. If you get the interferometer aligned then the beam intensity varies as function of the difference of beam path lengths.
I’m an optomechanical engineer and I’m sorry. I’m not impressed. In a Michelson, the single most important requirement is that the optical path lengths of the two arms do not drift with respect to each other, either in length or angle. Having that path length determined by a fused deposition polymer is about the LAST choice I would make. I have a suggestion. Fused quartz rods are relatively cheap. Buy some 6mm rods and a thin diamond blade to cut them to size. Use the 3D printer to make plate-like parts, ‘replicating’ a cage structure. The polymer parts should be used only for components PERPENDICULAR to the optical path. You could even experiment with using embedded rods to stabilize the plates in various directions. So much of hobbyist activity amounts to a kind of adult coloring or copying. Rather, at your own level, try to be a scientist.
Over $3K for a similar setup from Thor Labs (1). Wow, you can buy everything here <i>including the 3D printer</i> for that. Good work!<p>1: <a href="https://www.thorlabs.com/michelson-interferometer-educational-kit?tabName=Overview" rel="nofollow">https://www.thorlabs.com/michelson-interferometer-educationa...</a>
With products from a vendor like Thor Labs, you're getting a lot of quality and knowledge built into the system. Mechanical engineers, electrical engineers, optical engineers... all of which means an edu kit like that will train a student to be useful in most grad research labs (which often build their systems out of thor labs components).<p>It sort of depends on what your goal is; personally, I live to see something expensive on Thorlabs, and make a simplified, less accurate, and far cheaper alternative in my home lab. But that's rarely how folks in labs do it- instead, they will focus on getting people to be useful for performing state of the art research, which usually depends on applying hundreds of years of experience to make some tiny marginal improvement, which frequently depends on having extremely precise and accurate gear.
Hopefully you enjoyed the post then!<p>I think there's just such a huge middle ground that's missing (for funny historical reasons[1]) between "children's toy" and "lab-grade equipment" especially in optics, which is why I was excited to make this my first foray into making a fully 3d printed "useful-ish" thing that doesn't really exist otherwise.<p>---<p>[1] This is because most lab equipment was made _in the lab_ back in the 60s or so, and having this technical ability was a huge advantage for many labs. Now, personnel cost/hours are much more expensive relative to equipment, so people will pretty much pay whatever to get lab-grade stuff.
I haven't read the post yet because my work blocks access to the domain.<p>I agree there is a huge middle ground- for example, I make hobby microscopes at home, and much of my work has been making accurate and precise 2D/3D stages. It's easy to buy great, simple (non-motorized) scopes with good optical quality, but as soon as you start adding motorized stages, or any sort of complicated illumination or filtering, it gets challenging quickly. My actual goal is to track microbes in real time using computer vision, but the professional hardware to do so is out of my price range.<p>I have spent literally thousands of hours fiddling with one part or another Today, I'm working on a high speed flash illuminator that is coupled to the camera, and it's one problem after another. Reality has a fractal level of detail.<p>Since I haven't been able to look at your project yet, I don't know if you worked on this area, but I found it really useful to clone the Thorlabs cage system components: <a href="https://www.thorlabs.com/optical-cage-systems" rel="nofollow">https://www.thorlabs.com/optical-cage-systems</a> and specifically <a href="https://www.thorlabs.com/item/CXY2A" rel="nofollow">https://www.thorlabs.com/item/CXY2A</a> (you can download their 3D model and see that the mechanism isn't that complex).<p>Another thing I've ended up doing is prototyping in plastic and then having it machined at a place like JLCPCB out of aluminum. PLA is just flexible enough (especially under load) that it can make the results very frustrating.
As a student at a top worldwide university, I can tell you we order a lot more stuff off Amazon and eBay than you'd think. There's an awkward middle ground where you either buy something cheap or make it yourself because labour is basically free in academia thanks to the large amount of students and staff but grant money is not.
But what do you down with the Thorlabs Lab Snacks? I thought that was the main reason grad students ordered things from them.
yes ! but it also assumes you have: a good optical breadboard + bench + dampeners, a beautiful set of lenses, all sorts of nice lasers and kinematic mounts and linear stages etc etc<p>so yes, we _also_ (back in my phd lab) built equipment in that sense, but there was a pretty good foundation of Fairly Fancy stuff already sitting around !
In some cases, you'll learn more from crappy hardware than you will from lab-grade gear. This is probably one of those cases. This build will require thoughtful attention and debugging/optimization on the student's part in ways that the Thor Labs kit might not.<p>I mean, it's practically the most basic optical experiment that you can perform. Nobody needs to pay $3K to learn how an interferometer works. It's not a MoT or something exotic like that, it's a beam splitter and a couple of mirrors.<p>Put another way, it's the difference between building a Heathkit and putting a bunch of parts together that you salvaged from other stuff, for those who are old enough to grasp <i>that</i> analogy.
Ironic isn't it, since Thorlabs brought down the cost of optical tooling and made components more accessible - they are the Amazon of optics and remain a cost leader.
Yeah, I don't mean to beat up on Thor Labs. As they point out, they don't even make any extra profit on those kits beyond the components themselves. And then there are the free snacks. :-P<p>If you are putting together some more advanced educational or experimental apparatus, they are pretty much a no-brainer supplier, as you say. But their level of quality, support, and system integration just isn't necessary for something like this.
ha, thanks!<p>that one has uhh substantially less drift for what it's worth, but reprinting in more stable material would help that a ton (and still be quite cheap!)
I was a teaching assistant for freshman physics lab while in grad school, almost 40 years ago. My co-teachers were all theoreticians, so I bore the brunt of helping the students troubleshoot their setups.<p>There's a balance that has to be struck between: 1) Equipment that's so perfect that students learn nothing about the effort to get an experiment working. 2) Or so crappy that it's an obstacle to learning anything at all.<p>Also, the crappy-ness is multiplied by 30 for the number of setups needed for a class of 60 students, assuming they work in pairs.<p>Oh, the crappy oscilloscopes. They were cheap "student scopes" and their controls were worn out, so they behaved erratically. Since then I've met other people who took freshman physics lab, and they remember the "oscilloscope lab" with disgust.
Same physics principles used to measure gravitational waves at LIGO (Laser Interferometer Gravitational-Wave Observatory)but just much, much smaller. Very neat!
HN hug of death, oh no!<p>Wayback machine to the rescue:<p><a href="https://web.archive.org/web/20260109203451/https://guille.site/posts/3d-printed-michelson/" rel="nofollow">https://web.archive.org/web/20260109203451/https://guille.si...</a><p>Very cool project!
you can go much cheaper if you use a microscope slide or similar as the "beam splitter". Its not 50/50 so the fringe contrast will be lower, but in interferometry one is typically more interested in maintaining the position of a peak or number of peaks traversed...<p>alternatively one can use a more grazing sharper angle of incidence to bring it closer to 50/50 beam splitting, but then the internal reflections become stronger and the setup is no longer a nice orthogonal one (but how often is that really necessary for a task?)
yeah I cheated a little bit, but<p>> Ok, time to confess: I did cheat a little in calling it the “cheapest” Michelson interferometer, since technically even this beam splitter is like 16 USD, but it is very possible to use a microscope slide instead at the cost of some contrast, which will net out to < 20 cents, even at pretty expensive per-unit prices.<p>:)
Neat. Perhaps one can use it to see PLA creep in real time.<p>(not a joke, I'd actually like to see that)
Not creep, but thermal expansion is definitely noticeable with interferometry: <a href="https://www.youtube.com/watch?v=vupIq4epCQA" rel="nofollow">https://www.youtube.com/watch?v=vupIq4epCQA</a>
Oh absolutely!<p>I would not actually use this for uhhh, repeatable measurements over any extended period of time!<p>(If that were the case, I'd recommend re-printing it in a slightly more stable material, or just CNC milling the mounts out of aluminum using some of the ~$1-2K aluminum desktop mills and using some aluminum extrusions as the base.)
Nice project! This video: <a href="https://www.youtube.com/watch?v=5nBY4Y0bicM" rel="nofollow">https://www.youtube.com/watch?v=5nBY4Y0bicM</a> explains why the original interferometer was designed in the first place: to detect a hypothetical luminiferous ether, before Relativity theory made it unnecessary.<p>It's important to say the original interferometer was much less elegant -- there were no lasers in 1887. But it did have a solid stone "boat" floating in a little lake of mercury. Not making this up.
Very neat design. I work with high-end interferometry but really have an itch to build something like this just for fun. I'll go ahead and add a cheap camera (which I already have) in the image plane and hook it up to my interferometry software (wavefrontpro.com) to make it even more fun and useful! :)
That was a cool physics lab I did (disproving ether) and also measuring the speed of light through lucite... other cooler ones like helmholtz coils, wax lens focusing microwaves, measuring gravity, etc...<p>Wish we worked on IMUs, I still need to get down quaternions
Yes! Michelson interferometers are an amazing first lab experiment since it teaches you the basics of a bunch more techniques which are handy in more advanced experiments, while still having a satisfying outcome when done correctly (which is not as finicky as other experiments with less fun outcomes).
I wish that humans were not so easily duped into believing that things for which someone else uses the same name are really the same and things for which someone else uses different names are really different.<p>The Michelson–Morley experiment was indeed very important, but it has not proved in any way the non-existence of ether. It has just proved that the ether does not behave as it was previously supposed, i.e. like the materials with which humans are familiar.<p>It does not matter at all what names are used for it, one may choose to name it "ether", "vacuum", "electromagnetic field", "force field" or anything else, but all the modern physics, since James Clerk Maxwell and William Thomson, is built on the assumption that the space is not empty, but it is completely filled with something that mediates all the interactions between things.<p>Only before the middle of the 19th century, the dominant theories of physics assumed the existence of true vacuum. The existence of true vacuum is possible only in the theories based on action at a distance, like the Newtonian theory of gravity or the electromagnetic theory of Wilhelm Eduard Weber, but not in field-based theories, like the electromagnetic theory of Maxwell or the gravitational theory of Einstein.<p>It is rather shameful for physics that the main result of the Michelson-Morley experiment has been the replacement of the word "ether" by "vacuum", as if a change of name would change the thing to which the name is applied, instead of focusing on a better understanding of the properties of the thing for which the name is used.
"Ether" is a hypothetical substance with certain properties. The Michelson-Morley experiment proved that no substance with those properties existed. There's something else with different properties, so it makes perfect sense to use a different name.
In context of approximately everyone's education, the history goes like this: in the past people believe there's <i>something</i> in empty space, and used the name "ether" for that. You learn that, then you learn that MM showed there's no "something", no "ether", but that empty space is, in fact, empty, which is what "vacuum" means. And then if you pay attention or any interest to the topic, you learn that there in fact is no pure vacuum, there's always "something" in empty space.<p>The obvious question to ask at this point is, "so ether is back on the table?".<p>Turns out the mistake is, as GP said, thinking MM proved space is empty; it only disproved a particular class of substances with particular properties. But that's not how they tell you about it in school.
More specifically MM showed that earth is not moving relative to a hypothetical medium through which electromagnetic waves propagate. So either the universe is geocentric or there is no such medium.
It's more than just the lack of material. It demonstrates that light propagates in a specific way that is different from any ordinary material. Light moving in a vacuum is different from a baseball moving in a vacuum. The speed of light is independent of your own motion, which is not true of anything with mass.
> The Michelson–Morley experiment was indeed very important, but it has not proved in any way the non-existence of ether. It has just proved that the ether does not behave as it was previously supposed, i.e. like the materials with which humans are familiar.<p>That's kind of like saying that our failure to observe invisible pink unicorns does not prove the non-existence of invisible pink unicorns, it just proves that invisible pink unicorns don't behave the way you expect them to.<p>Luminiferous ether was a specific hypothesis about how light works. It made a prediction, which turned out to be wrong, which falsified the theory. Whether you want to attach the description "proves the ether does not exist" or "proves the ether does not have the properties ascribed to it by the theory" is completely irrelevant.
I thought the whole point was if it did exist the motion goes faster in one direction than the other.<p>edit: not sure if you're referring to dark matter<p>yeah I gotta read your comment more thoroughly
> I thought the whole point was if it did exist the motion goes faster in one direction than the other.<p>No, the idea was that, in a space filled with the hypothetical ether, Earth's velocity through the ether should have been detectable by comparing light beams traveling in different directions.<p>The null result was very important -- it didn't prove the absence of an ether, it only showed that it wasn't a factor in light propagation.
Really cool project. I’ve seen sometimes cheap lab clean outs on ebay which can be cool toys, but this is on a different level.
I kind of wished there were more details around the tension springs and steel rods.
Use corner cube retroreflectors instead of flat mirrors.