Question:Possibilities to use the dvd in reflection in the spectrometer ?

by vnourrit | September 20, 2019 12:42 | #20939


Regarding the lego spectrometer, is there no way to use the dvd in reflection rather than in transmission ? To avoid the the tricky splitting process.



2 Comments

Hi @vnourrit, when you write "tricky splitting process" are you referring to having to manually peel apart the flat layers of the DVD?

If so, the answer if one is using a DVD as a diffraction grating, unfortunately, is no -- we need the light to pass through the finely ridged layer and be separated into wavelengths that can be analyzed. However, you can purchase a diffraction grating online for slightly more money that would be ready to use -- no splitting or peeling needed!

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A DVD has a very wide dispersion, so wide that a whole spectrum is hard to obtain. To many lines / mm and the dispersion is doubled by the mirror layer. A CD might do the trick, although even that is quite wide.

However, the reflective layer is not difficult to remove: soak the disk overnight in a dish with a mix of hydrochloric acid and hydrogen peroxide. the printing ink on the back can be stripped by paint remover. Don't use the -rw variety as they have a bluish hue. One more unnecessary thing to calibrate...

I mounted a fragment sawed and filed to size in an old 49 mm filter ring with the glass removed, so I can easily screw it on my Sony NEX kit lens. The spectrum is recorded against a dull black panel.

To disassemble filters and optical gear cheaply and securely, I use putty knifes ground to size

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