The device uses two CDs, stripped of their reflective coating. This leaves the plastic layer behind, which appears to be acting as a circular diffraction grating. By passing light from a flashlight through a CD, a dazzling rainbow vortex is created, and the effect is even further improved by adding a second disc. The patterns can be moved and shifted by changing the distance between the discs themselves, as well as the flashlight. This is achieved through the use of a sled that slides on PVC pipes, holding each individual element.
It’s a build of a kind we haven’t seen before, and is put to good use as a creepy Halloween decoration, imitating the famous Cheshire Cat. It’s one we can’t wait to tackle ourselves, and we wonder how difficult it would be to turn it into a projection, or a larger scale design.
The video starts with a basic discussion on the principles of diffraction gratings. The basis of the work is a commonly available diffraction grating, readily available online. It’s a plastic sheet with thousands of microscopic ridges scored into the surface. The overarching method to create a candy version of this is simple — coat the ridged surface in liquid chocolate or sugar syrup, to transfer the impression on to the candy surface when it solidifies. However, the video goes further, explaining every step required to produce a successful end result. The attention to detail is on the level of an industrial process, and shows a mastery of both science and candy processing techniques. If you’ve ever wondered how to properly crystallize chocolate, this video has the knowledge you need.
It’s not often we see candy optics, but we like it — and if you fail, you can always eat your mistakes and try again. If you’re wondering what you can do with a diffraction grating, check out this DIY USB spectrometer.
Obviously the wavelength of a laser can’t be measured with a scale as large as that of a carpenter’s tape measure. At least not directly and that’s where a Compact Disc comes in. [Styropyro] uses a CD as a diffraction grating which results in an optical pattern large enough to measure.
A diffraction grating splits a beam of light up into multiple beams whose position is determined by both the wavelength of the light and the properties of the grating. Since we don’t know the properties of the grating (the CD) to start, [Styropyro] uses a green laser as reference. This works for a couple of reasons; the green laser’s properties don’t change with heat and it’s wavelength is already known.
It’s all about the triangles. Well, really it’s all about the math and the math is all about the triangles. For those that don’t rock out on special characters [Styropyro] does a great job of not only explaining what each symbol stands for, but applying it (on camera in video below) to the control experiment. Measure the sides of the triangle, then use simple trigonometry to determine the slit distance of the CD. This was the one missing datum that he turns around and uses to measure and determine his unknown laser wavelength.