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DVD vs. Diffraction Grating on Amazon / eBay

by familysimon new contributor | October 22, 2019 15:54 | 156 views | 3 comments | #21261 | 156 views | 3 comments | #21261 22 Oct 15:54

Processing a DVD to get a diffraction grating looks like so much work. Amazon and eBay have linear diffraction gratings available in bulk -- package of 25 for $12.00 looks like a deal. Key is buying a LINEAR single-axis grating film (multi-axis won't work for a spectrometer). I just ordered the slide pictured, will try it out... Anyone have comments or suggestions on this?

I'm making an integrating sphere for use with my spectrometer so I can calibrate light bulbs, I'll try to document the build and post it back here...


3 Comments

Hi @familysimon! Glad you are finding a diffraction grating that you like. Maybe for fun sometime you can cut up an old DVD and see how that goes for comparison. :) Keep us posted how your project goes :D

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So I think I can be of some help here, I use these gratings in my spectrometer. They are cheap, and consistent, but a little fragile. I keep a stack of them in case I smudge or warp it. The maximum these gratings go is 1000 lines per mm while DVDs go up to around 1300 lines per mm.

Pros: Easy to build around and mount, no cutting required, 1um is an easy calculation to use.

Cons: a little fragile being a film vs thicker plastic, DVDs have a higher line per mm count, DVDs are more widely available.

Unlike ruled gratings, which are have a profile of a square wave, these holographic gratings along with the DVDs, have a sinusoidal profile. This is why they transmit m = -1, 0, +1 instead of transmitting m = 2, 3 , ... ,(where m is the order of the node) like the expensive ruled gratings normally seen in physics labs. This has its benefits since less light is lost in the higher orders, so you can aim your sensor at the first order and call it a day.

Additionally, these gratings will also reflect a first order, which might have some applications. I'm told these gratings are made holographically whereas DVDs are injection molded, but I'm stretching what I know here.

Anyways, you can message me for some calculations and sources to help with your project.

@win215 Thank you for your input, I just received the grating slides and I'll dismantle a DVD or two and do a comparison when I finish the spectrometer build (kit ordered). I'm making an integrating sphere: I want to test a large quantity of BR30 light bulbs (mostly LED, but some incandescent), measuring color temperature and matching the bulbs up is the immediate goal. Thank you for providing the "science behind the grating."


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