Infrared spectrophotometer DIY

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Discussion Overview

The discussion revolves around the construction of a DIY infrared spectrophotometer for analyzing organic compounds, focusing on functional group analysis and compound fingerprinting. Participants explore various design approaches, sensor options, and practical challenges associated with building such a device.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses a desire to build a spectrometer that operates in the range of 2.5 µm to 25 µm and seeks advice on monochromator construction and suitable sensors.
  • Another participant suggests considering a Fourier-transform infrared (FTIR) design for its simplicity and fewer moving parts.
  • A different participant shares past experience with CO2 lasers and discusses the use of thermopiles and thermistors as sensors, while also mentioning the potential of pyroelectric detectors, particularly for the far infrared range.
  • Another suggestion involves using a bar scanner as a DIY option, highlighting the importance of resolution and the need for a suitable database for spectrum peak identification.

Areas of Agreement / Disagreement

Participants present multiple competing views on the best design approach and sensor options, indicating that the discussion remains unresolved with no consensus reached.

Contextual Notes

Challenges include the selection of appropriate sensors for the far infrared range, the complexity of creating a reliable database for spectral identification, and the varying effectiveness of different DIY methods proposed.

Ludek
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Hello everyone gathered here, I am passionate about chemistry and practical physics but the analysis of organic compounds is beyond my wallet and myself. So I want to build a spectrometer for functional group analysis and compound fingerprinting. The most commonly used range was from 2,5um to 24-25um (Wavenumber 4000 to 400 cm–1) And now the biggest problem will be receiving the signal and splitting the signal to be as monochromatic as possible.That's why I would like to ask how and what to make/buy monochrator. And what sensor would be best, thermocouple or something else
 
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Back in the day when I worked on CO2 lasers (@ 10um), thermopiles, thermistors, etc. were the only practical sensor. IDK, maybe there's something more exotic than just measuring heat now, but it won't be a normal semiconductor junction, especially at 25um.

Check out pyroelectric detectors too. IIRC, they weren't great for average power. OTOH we were at 100's of watts, so YMMV. 25um is still a problem, I think.

Ask Google about deep IR detectors, they'll know more than us, I think.
 
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While it may not work for far infrared a "bar scanner", 1 pixel wide, are DIY. By beam spreading lens and/or mirrors, or just increased distance from the diffraction grating to the bar scanner (reduced intensity) will increase the resolution. It should do near IR okay, and maybe get into the mid IR, depending on brand of bar scanner. Get 2000 dpi bar scanner. Or more, not a 300 dpi or even a 600. Used is cheaper for your first model. Find instructions on several websites/pages. I did. Get a 1 foot bar scanner, not a 1 inch. A discarded page scanner can be disassembled for it's bar scanner. The instructions to make an Arduino to read the bar scanner is online as well.

I think your greatest problem will be creating the database. There are some free ones but they are incomplete. The commercial spectrum peak identification databases are expensive, when I priced them 5 years ago, at over 2,000 USD. At that price, might as well buy the device that comes with the software and database.