Diffraction Spectrometer

This morning before a physics tutoring session on optics, I had a few minutes to make a spectrometer for the session.

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This spectrometer acts a lot like a prism by separating the light into the colors which make it.

Any element or molecule can only give off light at certain frequencies (colors).   You can figure out what element something is by comparing its spectroscopic readout to its established “fingerprint.”   You may try this with fireworks, fluorescent light, or burning of pretty much anything (safety first of course).

In order to make it I cut a square hole on one side of a box (either left or right side).   Then on the opposite side of that hole I cut a very narrow vertical rectangle.  The thinner this rectangle the better the resolution, but the wider it is the brighter your readout will be.

Then I cut out a piece of diffraction grating and placed it onto the square hole with tape.

Viola!  Its really that easy.

Here are some videos demonstrating the work:

If you are not in the mood to experiment, I placed the precise dimensions for my manifestation of the device below:

Tools and Box Used

From left to right: cardboard box, knife, box cutter.

Here you can see what the box looks like when closed (has the diffraction grating).

Measurement for the width for Diffraction Grating Hole

Measurement for the width for Diffraction Grating Hole: 15.13 mm

Measurement for Height Of Slit

Measurement for Height Of Slit: 10.77 mm — not shown, width of slit is about 2mm

I should mention that there is a design decision when making the slit.

The thinner you make the slit the more precise your spectrometer,

but the dimmer the readout.

The wider the slit, the brighter the readout,

but each output line will be at least as wide as your slit.

I found that 2mm worked pretty well for my purposes.

Anyways, more dimensions:

Measurement For distance from Side of Box to Slit

Measurement For distance from Side of Box to Slit: 9.83 mm — however, there is probably no penalty for putting it closer (just showing this cuz it is what worked for me).

Distance from edge of box to the grating hole: 14.39 mm

Distance from edge of box to the grating hole: 14.39 mm — again probably doesn’t matter a whole lot, but this definitely worked for me.

same shot better lighting

I actually had to cut two holes for the grating, but I liked the ability to potentially swap different types of gratings in. I put the grating inside, as it was super easy to mount, and was stabilized by being sandwiched between the two sheets of cardboard.

Close up on Grating

Close up on Grating

Top Down View of Interior

Top Down View of Interior

Diffraction Grating Photo

Picture of the Diffraction Grating which I clipped a piece from for the spectrometer.

Same picture w/o flash

Same thing, just taken w/o flash (what it normally looks like)


These are the things I used to make it:

*A 1000 lines per mm  grating will create a spectrum wider than the 500 lines per mm grating, allowing better resolution.