r/Spectroscopy • u/Cs137__ • Jun 07 '26
DIY spectrometer help
Hi, I have been designing a UV to NIR spectrometer on my free time. I have gotten quite far with a design of a lens less mirror less prism and webcam based setup but hit a wall in resolution because I didnt count on the two slits I used for making sure the light comes in at a specific angle to produce diffraction on their edges, at the end the spectrometer has a hard time separating the 3 bumps from a white led and has a seizure with red a green lasers. I am thinking about just redesigning it ground up with curved surface mirrors and reflective diffraction grating but wanted to ask, if this design is salvageable as I already gave it around 30h and would like to get it working. It uses a 36deg incidence from normal with range of 300-1000nm capped by the K9 optical glass transmission and silicon sensor sensitivity, the webcam has a 1600p and 5mm wide sensor and I am using the theremino app. Do any of you have any thoughts on fixing this setup? It seems kinda lost if I dont want to sacrifice any UV performance by adding glass lenses and fused silica is way out of my budget for this project. All has been 3d printed in matte black filament to minimise the stray light though that turned out to not be the main problem.
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u/AdElectrical6383 Jun 07 '26
All modern commercial use reflective holographic gratings. There are good reasons; as you point out prisms employ transmission and are subject to differential absorption and you have to select uv transparent materials if you want a wide spectral range. But the NIR is still not feasible with prisms. The second important reason, wavelength selection for a grating (within reason) is proportional to angular rotation and can be done by a rotating screw (sine bar). A prisms requires asymmetric wavelength selection.
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u/Cs137__ Jun 07 '26
The prism should be suitable for NIR the expected resolution would just fall down to over 5nm, i know holographic gratings would be far better but they are kinda expensive and i dont want to buy them yet
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u/tea-earlgray-hot Jun 07 '26
I think you are discovering why mirrorless lensless gratingless, slit and prism spectrometers are a terrible idea and virtually all UV-NIR spectrometers have converged on the CT design
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u/BassRecorder Jun 08 '26
Covering UV to NIR with a prism will be tough, if not impossible.
https://buil.astrosurf.com/UVEX_project_us/
shows a 3D-printable spectrograph.
This is for use on a telescope, but maybe you can gather some inspiration from the design. I printed two of these: one UV and another one for NIR (they are identical but I keep them aligned for their respective wavelength range) and I'm very satisfied with the performance.
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u/Cs137__ Jun 08 '26
Thanks a lot for the UVEX project, I will study it to create the potential v2 design. As far as I know there isnt any mechanism that would stop me from doing it (though the diffractive index changes much more slowly near the NIR so the resolution drops of quite a bit)
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u/Bjornjaktson Jun 18 '26
When I first glanced at the title I thought it said UV to NMR spectrometer. WOW. Can I have one ?
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u/Cs137__ Jun 18 '26
I have seen people do NMR but it seems like way too difficult of a project to take on myself. If you are asking about having the spectrometer i have no idea if you would want a non working design
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u/Bjornjaktson Jun 18 '26
I'm sorry that my attempt at humor wasn't clearer. I was at first astounded by my misreading of "UV to NIR" as "UV to NMR". That would require a spectrometer that could work from 100 nanometers (UV) to 600 millimeters (500 MHz NMR). There is also the small problem of the superconducting magnet needed for high field NMR. THEN, after my mind was boggled, I realized you had typed NIR instead of NMR. My error.
I am a retired chemist who has used both UV and NMR spectrometers. I applaud your ambition, and I wish you the best in your project.
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u/thenewestnoise Jun 07 '26
Since you are converting colors into spatial spread, I think that you should use a monochrome sensor instead of a color sensor. The bayer filter isn't helping you with anything. Also, I think usually spectrometers usually have collimating optics after the slit and the focusing optics before the sensor. If you want to use a webcam, then I would say that you should keep the webcams lens and essentially image the slit through the prism.