How to make a Spectrometer

The procedure to make a DIY spectrometer

Spectrometers are useful devices in measuring starlight, light sources, and concentrations of samples. Here I will show you how to build one of your own. What is perceived as light is often a combination of several different wavelengths with different intensities. A spectrometer is a device that can split light into its component wavelengths and intensities. I’m going to show you how to build a spectrometer of your own.

Materials:

  • Tissue box
  • Utility knife
  • Strong tape (Packing/vinyl tape is ideal)
  • Hot glue gun
  • Hot glue sticks
  • Diffraction grating (available from Amazon)
    • Should be holographic (cheaper than mechanical)
    • Small ones should do. Large rolls are unnecessary
    • Ideally, it should have a small paper/carboard frame around it to prevent it from bending
  • Popsicle sticks (if necessary)
  • Light source
    • In mine, I used a phone LED
    • If that doesn’t work, try LED lightbulbs, flashlights, or other LED light sources
    • If wanted, a color-mixing LED bulb can be used for an even spectrum
  • Tape
  • Room with ability to darken (light switch, blackout window coverings, door)
  • Webcam
    • Household webcams will do; no need for expensive, high-res webcams
    • Ensure it does not get washed out by light too easily
    • Ideally, it should have a hard piece(s) behind the lens portion to simplify mounting
  • Flat surface
  • Additional light sources for testing emission spectrum
    • Streetlights, CFL lamps, car light, etc. all work
  • Additional substances for testing absorption spectrum
    • Olive oil
    • Sunflower oil

Note: In some spectrometers, a collimator is used to better use the light from the slit. I find little use in collimators, as in DIY setups they add negligible quality with added complexity.

Procedure:

  1. Use the utility knife to cut off the top of the box
    1. Preserve the cut top piece; you’ll need it later
    2. The top should be the largest face, the side the middle, and front the smallest face
  2. Use the utility knife to cut off a 2x4 cm rectangle from the front of the box
    1. The rectangle should be 4 width x 2 height when the box Is oriented with the front facing you and the top facing up
  3. Build the slit assembly
    1. Take a packet of 2 razorblades and fold the edges inward
      1. The packet should be just wide enough to snugly fit each blade
      2. Use hot glue if necessary
      3. Cut off the back to create an open space
      4. Staple it together so it holds its shape
    2. Secure the first razorblade at the bottom, using hot glue to keep it secure
    3. Insert the second razorblade at the top of the now-created slot
    4. Adjust it to create a small slit with the razorblades
  4. Tape this slit assembly to the 2x4 cm hole that was made
  5. If necessary: Use popsicle sticks to reinforce the frame
    1. On several diffraction gratings, the paper frame is extremely weak and vulnerable to bending. This is dangerous for the diffraction grating, as it must not be bent
    2. Use a scissor to cut 4 popsicle stick pieces, each 1 cm smaller than the horizontal (should be the longest, and the top and bottom when diffraction grating is positioned upright)
    3. Hot glue each popsicle stick to the long side of the diffraction grating on both sides and top and bottom
  6. Insert the diffraction grating
    1. Note: If the diffraction grating frame edges is too thin and it is hard to mount into place, add 2 identical small objects on both sides (small dominoes) to increase the base
    2. You have two choices: Using glue or strong tape
    3. If using strong tape: Form a roll and stick it under diffraction grating
    4. Position It in line with the slit, so in the middle
    5. It should be roughly 12 cm away from the back for a 10 cm wide box, or 6n/5 cm away from the back of a n cm wide box
    6. Place it parallel to the front/back side of the box, and rotate it 30 degrees CW if you’re right handed or 30 degrees CCW if you’re left handed
    7. If using glue: Glue it into place from the sides
  7. Create viewing hole for the camera
    1. If you’re right-handed, the back-right (when front faces you and top points up) edge of the box is where the viewing hold goes
    2. If you’re left-handed, the back-left (when front faces you and top points up) edge of the box is where the viewing hold goes
    3. Cut out that corner as specified:
      1. Do not cut the bottom at any time.
      2. Cut into the left/right side of the box from the bottom-right/left-back corner 6 centimeters and cut directly up from there until that portion is removed
      3. Cut into the back side of the box from the bottom-right/left-back corner 6 centimeters and cut directly up from there until that portion is removed
  8. Mount the camera
    1. If no hard piece behind: Cut a roll of strong tape and stick it below the webcam
    2. If hard piece: Cut a 8 cm long piece of strong tape and stick the middle of it to the hard piece
    3. Open a camera app on your device
    4. Darken the room and pass light through your slit
    5. The camera should be able to see the spectrum
    6. If not, adjust the camera so the spectrum is visible on the screen
    7. Try to adjust to center the spectrum on the screen as best as possible
  9. Cover the top of the spectrometer box with the top piece that was put aside
  10. Using a light source, adjust the slit so a thin spectrum is visible
  11. You have your spectrometer!
    1. You can test its ability to measure emission spectra by pointing the slit at different light sources (Streetlights, CFL lamp, car light, etc.)
    2. You can also test its ability to measure absorption spectra through the next article

Conclusion: Spectrometers are devices with several uses. They might seem like complex lab equipment, but really they’re simple light physics that can be done at home.