Diffraction gratings are beautiful things, bending transmitted and reflected light and splitting it into its component wavelengths to create attractive iridescent rainbow patterns. It’s the same effect you see on the bottom of a CD!
You can 3D print a functional diffraction grating, too, with the right techniques, as it turns out! The average 3D printer can’t recreate the tiny-scaled patterns of a diffraction grating directly; a typical diffraction grating may have up to 1000 lines per mm. Instead, by 3D printing onto an existing diffraction grating, the print can pick up the texture on its base layer. It’s a great way to add iridescence and shine to a print.
We’ve seen similar work before, but the guide from [All3DP] goes into greater detail on how to get the effect to work just right. Getting the bed as close to perfectly level is key here, as is the first layer height. This is because the first layer of plastic has to meld perfectly with the diffraction grating to pick up the pattern. Too high and the grooves won’t transfer to the plastic, and too low, and it’s likely you’ll just melt the grating itself. Setting the Z-offset appropriately can help here.
Choosing the right bed temperature is also important to ensure the molten plastic is able to flow into the grooves of the grating. Again, the temperature at which the diffraction grating itself can survive is important to take into account; going above 90 degrees can be risky here. The guide also shows two methods of achieving the goal: one can either use an off-the-shelf grating, or one can prepare a no-longer-wanted CD into a suitable print surface.
Naturally, removing the print must be done delicately, lest one disturb the delicate structures key to generating the iridescent effect. [All3DP] recommends using a freezer to help separate the parts from the grating surface. It also bears noting that the print won’t survive excessive handling, as the grating structures will get damaged by physical touch.
It’s a great in-depth guide on how to get diffraction grating prints right. Meanwhile, consider diving deeper into the world of 3D printed optics!
[The Action Lab] had a very serious technical problem. His daughter wanted to 3D print sparkly unicorns. But how do you make a 3D print sparkly? Turns out, he had used a diffraction grating before to make rainbow-enhanced chocolate.
The method turns out to be surprisingly simple. Using a diffraction grating as a print bed, puts the pattern on the bottom of the 3D print and — thanks to how a diffraction grating works — the 3D print now works like a grating, too.
A monochromator is an optical instrument that permits only a narrow selection of wavelengths to be transmitted from a source, and the particular model [Doug] obtained renders visual light monochromatic by way of a mechanically-adjusted system of mirrors and diffraction gratings that allows only the selected wavelength to pass. The big dial is how the operator selects the desired wavelength, and is labeled in ‘mu’ (or milli-micro), but [Doug] helpfully points out the more modern term for that is nanometers.
How does it work? Light enters the device via an opening at the base, and only the selected wavelength exits from the top. The dial’s range is from 450 nm to 640 nm (representing violet-blue to red), which [Doug] demonstrates by shining a white LED flashlight into the unit and showing how only green, red, or blue will exit from the top depending on the setting of the dial.
An interesting side note is that with this particular device, images can be rendered monochromatic but otherwise remain intact. [Doug] demonstrates this by viewing a small section of his LCD monitor through the device, as shown in the photo he managed to capture.
It’s an interesting piece of vintage equipment that shows what is possible with passive optical components and a clever mechanical design. These devices are therefore entirely manually-operated tools (at least until someone sticks a stepper motor to the adjustment dial to create an automated scanner, that is.)
Here’s a great picture from [Jelly & Marshmallows] that shows off the wild effects of melted chocolate poured onto a diffraction grating. A diffraction grating is a kind of optical component whose micro-features act to disperse and scatter light. Diffraction gratings are available as thin plastic film with one side that is chock full of microscopic ridges, and the way light interacts with these ridges results in an iridescent, rainbow effect not unlike that seen on a CD or laserdisc.
It turns out that these micro-ridges can act as a mold, and pouring chocolate over a diffraction grating yields holo-chocolate. These photos from [Jelly & Marshmallows] show this effect off very nicely, but as cool as it is, we do notice that some of the letters seem a wee bit hit-or-miss in how well they picked up the diffraction grating pattern.
Fortunately, we know just what to suggest to take things to the next level. If you want to know more about how exactly this effect can be reliably accomplished, you’ll want to check out our earlier coverage of such delicious optics, which goes into all the nitty-gritty detail one could ever want about getting the best results with either melted sugar, or dark chocolate.
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.