[HN Gopher] The likely cheapest home-made Michelson interferometer
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The likely cheapest home-made Michelson interferometer
https://web.archive.org/web/20260109203451/https://guille.si...
Author : LolWolf
Score : 119 points
Date : 2026-01-04 20:49 UTC (6 days ago)
(HTM) web link (guille.site)
(TXT) w3m dump (guille.site)
| RationPhantoms wrote:
| Same physics principles used to measure gravitational waves at
| LIGO (Laser Interferometer Gravitational-Wave Observatory)but
| just much, much smaller. Very neat!
| LolWolf wrote:
| thanks !
| mturmon wrote:
| Michelson interferometry is also used to measure the spatially-
| resolved velocity and magnetic field of the solar photosphere:
| https://en.wikipedia.org/wiki/Solar_Dynamics_Observatory ->
| Instruments
| touchadinosaur wrote:
| 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.
| LolWolf wrote:
| Thanks ! Still need to upload it to Printables etc. Maybe this
| will finally get my ass a bit more into gear.
| alnwlsn wrote:
| Neat. Perhaps one can use it to see PLA creep in real time.
|
| (not a joke, I'd actually like to see that)
| zokier wrote:
| Not creep, but thermal expansion is definitely noticeable with
| interferometry: https://www.youtube.com/watch?v=vupIq4epCQA
| LolWolf wrote:
| yeah, even breathing nearby this thing (or putting a
| soldering iron near the paths) will show a visible change!
| LolWolf wrote:
| Oh absolutely!
|
| I would not actually use this for uhhh, repeatable measurements
| over any extended period of time!
|
| (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.)
| bigiain wrote:
| I suspect they'd be fairly cheap to get made at somewhere
| like JLCCNC. Or maybe get them to 3D print them in metal for
| you?
|
| I wonder if they have enough different metal choices that you
| could build a thermal expansion compensated version?
| https://patents.google.com/patent/US8292537B2/en
| LolWolf wrote:
| i'd probably just get it milled only if you had the CNC
| handy, the complexity isn't enough to justify 3d printing
| it in metal (probably a decent bit more expensive too!)
|
| but at "get it done in JLCCNC" prices I think a thorlabs
| mount is probably in your future :)
| bigiain wrote:
| I'd be surprised? If you have spare time, I'd be
| fascinated to see what their website magic quote tool
| tells you if you just upload your 3d files. Based on
| other projects I've seen using them I'd guess under
| $100...
| LolWolf wrote:
| sure ! I'll give it a try a little later once I'm at a
| computer !
|
| (you can too, if you'd like, the CAD files are all online
| as .step files :)
| ge96 wrote:
| 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...
|
| Wish we worked on IMUs, I still need to get down quaternions
| adrian_b wrote:
| 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.
|
| 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.
|
| 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.
|
| 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.
|
| 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.
| ge96 wrote:
| I thought the whole point was if it did exist the motion goes
| faster in one direction than the other.
|
| edit: not sure if you're referring to dark matter
|
| yeah I gotta read your comment more thoroughly
| lutusp wrote:
| > I thought the whole point was if it did exist the motion
| goes faster in one direction than the other.
|
| 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.
|
| 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.
| SAI_Peregrinus wrote:
| "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.
| TeMPOraL wrote:
| In context of approximately everyone's education, the
| history goes like this: in the past people believe there's
| _something_ 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.
|
| The obvious question to ask at this point is, "so ether is
| back on the table?".
|
| 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.
| lisper wrote:
| 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.
| zmgsabst wrote:
| Another interpretation is that the apparatus and not just
| light is made from ether -- and so the signal is lost
| because the measuring apparatus is also subject to the
| local distortion.
|
| That interpretation is also consistent with LIGO: we can
| detect _those_ ether disturbances because the distortion
| of our motion on the apparatus doesn't cancel the signal
| in the same way.
| lisper wrote:
| > Another interpretation is that the apparatus ... is
| made from ether
|
| Or maybe an invisible pink unicorn is sneaking into the
| lab at night and tweaking things.
| jfengel wrote:
| 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.
| lisper wrote:
| > 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.
|
| 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.
|
| 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.
| LolWolf wrote:
| 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).
| zokier wrote:
| > 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
|
| 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.
| LolWolf wrote:
| For sure! I didn't _quite_ want to get into the mechanics of it
| (assuming anyone who is interested would just take a peek at
| the wikipedia or any YT video).
|
| But yes :)
| NetMageSCW wrote:
| I kind of wished there were more details around the tension
| springs and steel rods.
| LolWolf wrote:
| what type of details would you like to see? happy to add more
| if helpful!
| bigiain wrote:
| I have a related question, how far are you turning the
| thumbscrews when making adjustments?
|
| I think M3 standard thread pitch is 0.5mm, so to a first
| approximation that almost 1000 wavelengths (if I have the SI
| units right in my head, and I'm not 3 orders of magnitude
| out?). I suspect the left/right and up/down adjustments have
| as fairly high lever ratio, but I can't imagine you could
| successfully adjust the in/out distance with any precision
| (not in the 690nm sense anyway)? Is the in/out distance not
| important so long as the beams are aligned?
|
| Dunno if you've seen it, but there's a great youtube video
| explaining how the actuators to align the James Webb mirrors
| work: https://m.youtube.com/watch?v=5MxH1sfJLBQ including a
| 3D printable version of them:
| https://www.thingiverse.com/thing:5232214 "This is a replica
| of JWST's mirror actuators. Six of these actuators are paired
| into a hexapod / stewart platform arrangement and used to
| control 6 degrees of freedom of each mirror segment (tip,
| tilt, roll, x, y, z translation)."
| LolWolf wrote:
| Ooh, great question. Usually fractions (~1/20th?) of a turn
| for alignment, it's hard to go below that since the mounts
| are so small and the springs don't have the tension to keep
| it super stable. (This is plenty for such a "coarse" set up
| like a Michaelson but might not be up to par for more
| delicate ones. This can be improved very easily but it was
| enough for this experiment!) If you want to observe
| something on the outputs, you have to do something like
| exhale on one of the arms or put a soldering iron near one
| of them--merely touching one of the screws gives you
| indiscernible output, even if the mirrors are aligned.
|
| Very interesting re: JWT, I will definitely take a peek,
| thanks !
| CamperBob2 wrote:
| Over $3K for a similar setup from Thor Labs (1). Wow, you can buy
| everything here _including the 3D printer_ for that. Good work!
|
| 1: https://www.thorlabs.com/michelson-interferometer-
| educationa...
| LolWolf wrote:
| ha, thanks!
|
| 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!)
| dekhn wrote:
| 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).
|
| 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.
| LolWolf wrote:
| Hopefully you enjoyed the post then!
|
| 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.
|
| ---
|
| [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.
| dekhn wrote:
| I haven't read the post yet because my work blocks access
| to the domain.
|
| 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.
|
| 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.
|
| 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:
| https://www.thorlabs.com/optical-cage-systems and
| specifically https://www.thorlabs.com/item/CXY2A (you can
| download their 3D model and see that the mechanism isn't
| that complex).
|
| 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.
| LolWolf wrote:
| ah I see!
|
| Yes this is very cool (hope you make it open source :)
| but have you taken a peek at the openflexure project?
| They make a fully motorized 3-axis microscope that is 3d
| printed and relatively inexpensive
| (parts+motors+electronics - PLA net out to USD 250?)
|
| it's very cool! maybe you can also take some ideas from
| there :)
|
| https://openflexure.org/
| dekhn wrote:
| I don't particularly like the openflexure approach.
| Instead, I build stages similar to standard XY stages:
| https://www.asiimaging.com/products/stages/xy-inverted-
| stage... which uses standard motion components (linear
| rail and linear bearings, 3d printer style steppers), all
| of which gets mounted on aluminum extrusion (4040). Then
| the illuminator and camera just get mounted on the
| aluminum extrusion.
|
| It's pretty close to the Thorlabs Cerna,
| https://www.thorlabs.com/cerna-r-series-modular-
| microscopy-s... although I just do low-magnification
| light microscopy.
| LolWolf wrote:
| I see, what's the min step size you're going for?
| dekhn wrote:
| typically around one micron (which is about the same as
| one pixel with my objective and camera). I am not trying
| to take min steps. I'd rather have smooth motion, with
| fairly high accuracy.
|
| The current system I am building is mainly optimized
| around scanning large areas quickly; I have already
| demonstrated that I can create accurate stitches by
| moving, stopping, taking photo, repeat, but it's slow
| (due to the stopping) so I am working on an approach that
| keeps the stage moving constantly, but triggers a bright
| flash that freezes intermediate exposures. This gives a
| good 10X speedup over the simpler model of
| move/stop/photo/repeat but brings in a number of other
| challenges.
| LolWolf wrote:
| ah very cool, I see!
|
| good luck! are you posting updates anywhere?
| CamperBob2 wrote:
| 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.
|
| 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.
|
| 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 _that_ analogy.
| LolWolf wrote:
| I think that's very much right :)
| zipy124 wrote:
| 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.
| dekhn wrote:
| But what do you down with the Thorlabs Lab Snacks? I
| thought that was the main reason grad students ordered
| things from them.
| LolWolf wrote:
| 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
|
| 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 !
| zipy124 wrote:
| All of those parts can also be acquired through alibaba
| for a stiff discount off the thorlabs pieces though.
| Whilst some labs have fancy stuff going around, a
| significant amount don't and there isn't very good
| equipment sharing between labs at most institutions.
| CamperBob2 wrote:
| My personal rule: buy lasers from AliExpress, buy goggles
| from ThorLabs. .-)
| bloggie wrote:
| 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.
| CamperBob2 wrote:
| 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
|
| 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.
| analog31 wrote:
| 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.
|
| 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.
|
| 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.
|
| 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.
| DoctorOetker wrote:
| 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...
|
| 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?)
| LolWolf wrote:
| yeah I cheated a little bit, but
|
| > 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.
|
| :)
| observationist wrote:
| HN hug of death, oh no!
|
| Wayback machine to the rescue:
|
| https://web.archive.org/web/20260109203451/https://guille.si...
|
| Very cool project!
| LolWolf wrote:
| oops! ran out of netlify credits. should be good now !
| echelon wrote:
| This was really cool.
|
| Please do the delayed choice quantum eraser next and post it
| here!
| LolWolf wrote:
| thank you!
|
| and ha, that one requires a little more fancy equipment :)
| boothby wrote:
| Wikipedia links to an article with a fairly approachable
| looking setup for that!
|
| https://arxiv.org/abs/quant-ph/0501010
| LolWolf wrote:
| I think getting an electron source and creating a robust-
| ish adjustable set up is v doable, but is definitely more
| of a Real Project(TM) than this silly little
| interferometer :)
| aj7 wrote:
| 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.
| LolWolf wrote:
| it's an interferometer with like 5cm arms made for 3 bucks,
| it's not made to be anything other than a basic demonstration !
| tucnak wrote:
| Bro, they're offering quality advice. They are good to you.
| So, you really don't need to defend yourself!
|
| xxx
| LolWolf wrote:
| it is thoroughly _fine_ advice stated in a shitty way that
| misses the entire point of this cheap demo
| lutusp wrote:
| Nice project! This video:
| https://www.youtube.com/watch?v=5nBY4Y0bicM explains why the
| original interferometer was designed in the first place: to
| detect a hypothetical luminiferous ether, before Relativity
| theory made it unnecessary.
|
| 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.
| versterrie wrote:
| 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! :)
| LolWolf wrote:
| Sweet thanks!
|
| Yes definitely a great extension would be to add a camera in
| the image plane (alternatively, defocusing the image slightly
| and using a photodiode would also be fun!)
| realo wrote:
| Use corner cube retroreflectors instead of flat mirrors.
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