Image above: Taking good photos of the spectra produced by the Public Laboratory fold-up paper spectrometer.
Seeing Mathew's note about taking delivery on 2000 fold-up spectrometers put me over the top and I finally made one. I printed it on black construction paper, super-glued it together, and tried two different gratings: a piece of DVD-R and a piece of 1000 lines/mm diffraction grating film that I bought from (Edmund) Scientifics several years ago (it took me an hour to find it). I tried it with the only webcam I have (Microsoft LifeCam VX-6000) with acceptable results, but then I tried to figure out how each component contributes to the quality of the spectra. So I eliminated the webcam and took really good photos of the spectra with a DSLR and Micro-NIKKOR 55mm 1:3.5 lens. I tried three different entrance slits and both gratings and recorded spectra of my compact fluorescent desk lamp. The photos were uploaded to Spectral Workbench to make spectrographs (search for "clf_cfl").
The conclusion of the entrance slit trials is that narrower is better. The narrowest slit I made was about 0.2 mm wide. The 0.5 mm slit blurred the peaks quite a bit. The slit below is cut in black heat-shrink tubing material (not a great choice for flame spectroscopy).
The conclusion of the grating trials is that the DVD-R is almost as good as the grating film. I bought a square foot of the film for less than $10 (similar to this), so I have enough for 100-200 spectrometers. The spectrum displayed by the film is brighter than the DVD spectra, and I had trouble finding the first mercury line (404.7 nm) in the DVD spectra. But almost all the standard peaks below 650 nm are distinguishable with either material.
Above: Spectrum of CFL bulb with the PLOTS paper spectrometer with DVD-R grating. Note the curved lines. Peaks are identified below.
Above: Spectrum of CFL bulb with the PLOTS paper spectrometer with 1000 L/mm grating film. Peaks are identified below.
The spectrum below was made with an Ocean Optics HR2000 spectrometer that costs $4200. All of the peaks to the left of 650 nm are more or less distinguishable in the spectrum I made with the 1000 lines per mm grating film (peaks above 700 nm are in the infrared and are invisible to my DSLR). Only a couple of the peaks are missing only in the DVD spectrum. The calibration of the two spectra above differs by up to 5-10 nm (I guess because Spectral Workbench does a linear calibration and uses peaks 2 and 5).
Above: CFL spectrum from a $4200 spectrometer. See source
Numbered Peaks above
|Peak number||Species producing peak||Correct wavelength (nm)|
|3||terbium from Tb3+||~485 to 490|
|4||terbium from Tb3+||~543 to 544|
|6||likely terbium from Tb3+ or mercury||576.960 for Hg or ~578 for Tb|
|7||mercury or terbium from Tb3+||579.066 for Hg or ~580 for Tb|
|8||possibly terbium from Tb3+ or europium in Eu+3:Y2O3||~580|
|9||likely europium in Eu+3:Y2O3||~587|
|10||likely europium in Eu+3:Y2O3||~593|
|11||likely europium in Eu+3:Y2O3||~598|
|12||europium in Eu+3:Y2O3||~611|
|13||likely terbium from Tb3+||~625|
|14||likely europium in Eu+3:Y2O3||~630|
|15||likely europium in Eu+3:Y2O3||~650|
|16||likely europium in Eu+3:Y2O3||~661|
|17||likely europium in Eu+3:Y2O3||~687-688|
|18||likely europium in Eu+3:Y2O3||~693|
|19||likely europium in Eu+3:Y2O3||~707 and ~709|
|20||likely europium in Eu+3:Y2O3||~712|
|21||likely argon||758.9315 or 763.5106 (??)|