We know the effect of passing white light through a prism and seeing the color spectrum that comes out of the other side. It will not be noticeable to the naked eye, but that rainbow does not fully span the range of [Roy G. Biv]. There are narrowly absent colors which blur together, and those missing portions are a fingerprint of the matter the white light is passing through or bouncing off. Those with a keen eye will recognize that we are talking about spectrophotometry which is identifying those fingerprints and determining what is being observed and how much is under observation. The device which does this is called a spectrometer and [Justin Atkin] invites us along for his build. Video can also be seen below.
Along with the build, we learn how spectrophotometry works, starting with how photons are generated and why gaps appear in the color spectrum. It is all about electrons, which some of our seasoned spectrometer users already know. The build uses a wooden NanoDrop style case cut on a laser engraver. It needs some improvements which are mentioned and shown in the video so you will want to have some aluminum tape on hand. The rest of the bill of materials is covered including “Black 2.0” which claims to be the “mattest, flattest, black acrylic paint.” Maybe that will come in handy for other optical projects. It might be wise to buy first surface mirrors cut to size, but you can always make bespoke mirrors with carefully chosen tools.
Aluminum tape is used to make the slit for passing the rainbow since it must have clean edges to let in the smallest sliver of light with no blurring, but this arrangement can always be upgraded to a pair of moveable razor blades. The laser cut edges are not clean enough or narrow enough. The diffracting material should be purchased since it is cheap and easy to find, but in a pinch, an unpainted CD will do the trick.
Theremino software is the weapon of choice, and a demonstration shows that a green laser pointer has a sharp spike in the green range and an additional peak in the infrared range. That is good news if you need an IR laser that you can also see in the visible spectrum. [Justin] covers some of the tests he plans to do, including quantifying DNA, and shows how inexpensive spectrometers can measure presence and saturation.