A LASER INTERFEROMETER MEASURES IN NANOMETERS - THIS ONE USES A 12 DOLLARS DIODE AND WINDOW GLASS
An open interferometer aiming for sub-micrometre precision over hundreds of millimetres, built from a cheap laser diode and a beam splitter ground from ordinary float glass.
WorkshopScience
Built withSTM323D printing
- difficulty
- ●●●●○
- time
- a weekend-plus
- license
- MIT
- repo
- repo ACTIVE147 stars
●●●●○ · a weekend-plus · MIT · 147 stars · repo ACTIVE
WHAT YOU’LL NEED
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COMPAREE VERDICT
This is a genuinely impressive piece of open hardware: a Michelson-style laser interferometer built from cheap parts, aiming for sub-micrometre precision over hundreds of millimetres, the job industrial laser calibration systems do. The core idea is sound: split a coherent laser beam, send the two paths to fixed and moving reflectors, and count the interference fringes as they recombine. The execution is clever: the beam splitter is ordinary 6 mm float glass with no coating, ground to size with a diamond whetstone in 3D-printed jigs, the laser is a roughly 12-dollar Osram PLT5 516FA diode chosen for its long coherence length, and the SFH229 photodiode costs about 70 cents. The repository has FreeCAD models (Version 5), KiCad sources for the boards with a ready JLCPCB package for the photodiode board, and STM32 firmware, all MIT licensed. The honest limitation is that it is explicitly a work in progress, with no written BOM or step-by-step guide. The single thing most likely to go wrong is alignment: a Michelson only shows fringes when both arms line up, and the repo has no written procedure for it. If you are comfortable with optics and laser safety, this is a remarkable foundation; if you need a parts list and a procedure, wait for the project to mature.
IN THE REPO
GOOD TO KNOW
- —FreeCAD mechanical models and KiCad electronics sources are in the repository, marked Version 5.
- —No bill of materials — part callouts are in the video and scattered across README sections.
- —KiCad sources for all boards; the photodiode board also has a ready JLCPCB production package, the others you export yourself.
- —No assembly guide or optical alignment procedure in writing — the build video shows it but there is no text walkthrough.
- —Project is marked work in progress and earlier design revisions exist; do not mix CAD versions.
- —MIT licensed, unrestricted.
Parts to buy
8 itemsFrom our check of the build. Exact quantities and part numbers are in the creator’s BOM.
Can I build this?
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
Videos
Laser Interferometer - Part 3: Mechanical Design
The creator's narrated Part 3: the new mechanical design and optical layout, choice of a low-expansion base plate, gluing the corner-cube reflectors and mirrors in place with printed templates, mirror alignment, the case and a demonstration. The beam-splitter grinding jigs are in the repository, not in this video.
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Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Watch the build video to see the mechanical design, reflector mounting and optical alignment in action (No written guide exists; the video is the primary documentation)
- 2.Clone the repository and open the FreeCAD models (Version 5) (Do not mix CAD versions — earlier revisions are in the commit history and dimensionally incompatible)
- 3.Export Gerbers from the KiCad photodiode and control board sources(The photodiode board has a ready JLCPCB package; export Gerbers for the control and laser diode boards from KiCad)
- 4.Source the Osram PLT5 516FA diode and 3mm photodiode before printing anything(Part numbers are in the README; no supplier links or full BOM)
Resources
Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.
KNOWN ISSUES
- Only the photodiode board comes with a ready JLCPCB production package; the control board and laser diode board are KiCad sources you export yourself, which can burn an afternoon if you have never done it.
- There is no written BOM: part callouts are in the video and README fragments, so you assemble the list yourself from multiple sources.
- Cutting and grinding the float-glass beam splitter to size takes patience: use the printed jigs and a diamond whetstone, keep the edges square and the faces clean, and you will only really know it is right when you see fringes.
- The project is marked work in progress and the CAD is at Version 5; mixing files from earlier commits will give you mechanically incompatible parts.
- Optical alignment is shown in the video but not documented in text — if you have never aligned a Michelson interferometer, expect multiple attempts.
- The Osram diode is Class 3B; enclose the beam path and never work with the laser at eye level during alignment.
How does this compare to a Renishaw XL-80 in actual accuracy?
The repository does not publish test data or a comparison. Its stated goal is sub-micrometre precision over hundreds of millimetres, and environmental stability, thermal drift and alignment all affect what you actually get. A Renishaw is a turnkey calibrated instrument; this is a work-in-progress open design.
Do I need an optical breadboard to build this?
No optical breadboard is needed, but the base matters. The creator wants a stiff, homogeneous base with near-zero thermal expansion: he moved away from a carbon-fibre bar, suggests glass-ceramic cooktop glass (even a broken one) and uses a plain glass sheet for the prototype. The optics are glued to it with 3D-printed templates, and any vibration or thermal expansion in the optical path will swamp the measurement.
Can I skip grinding the beam splitter and buy a commercial one?
You could, but the design is built around an uncoated float-glass splitter that uses the glass's natural reflectivity, ground to fit the 3D-printed mounts. A commercial part may need different mounts and give different beam intensities.
Is there firmware for reading out the fringes?
Yes. The repository has PlatformIO firmware for the STM32G431 on the control board (firmware/firmware_stm32g431), which samples the photodiode signals. It is work in progress and not documented in prose, so expect to read the code.
Community builds
No community builds yet — be the first, we feature the best ones.
Discussion1
FROM THE COMPAREE TEAM
A laser diode that costs about 12 dollars and a beam splitter cut from ordinary window glass, aiming for sub-micrometre precision over hundreds of millimetres. If you had this running, what would you measure first?
Diffraction Limited (0x23)
Diffraction Limited (GitHub: 0x23) is developing nmWave as an open interferometer for accurate distance measurement from low-cost, widely available components, documenting progress in a YouTube build series and an evolving repository.
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DISCLAIMER
- Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
- Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
- Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
CompareeTEAM1mo agoedited
Practical notes from verification: the repository is active, but the README itself says the project is work in progress and the CAD is marked as the new Version 5 design, so expect iteration. There is no single bill of materials file; the key parts, such as the Osram PLT5 516FA laser diode at about 12 dollars and the SFH229 photodiode, are named in the README. The STM32 firmware is published, and the photodiode board comes with a ready JLCPCB production package, while the other boards ship as KiCad design files you export yourself. The beam splitter is plain float glass about 6 mm thick, ground to size with a diamond whetstone in 3D printed jigs; it relies on the glass's natural reflectivity, with no coatings. If you are comfortable with optics and laser safety and can live with an incomplete parts list, this is a weekend-plus project; if you need step-by-step instructions, it is not ready yet. Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.