Throughout our day-to-day experiences, we come across or make use of many scientific principles which we might not be aware of, even if we immediately recognize them when they’re described. One such curiosity is that of caustics, which refers not only to corrosive substances, but can also refer to a behavior of light that can be observed when it passes through transparent objects. Holding up a glass to a light source will produce the effect, for example, and while this is certainly interesting, there are also ways of manipulating these patterns using lasers, which makes an aurora-like effect.
The first part of this project is finding a light source. LEDs proved to be too broad for good resolution, so [Neuromodulator] pulled the lasers out of some DVD drives for point sources. From there, the surface of the water he was using to generate the caustic patterns needed to be agitated, as the patterns don’t form when passing through a smooth surface. For this he used a small speaker and driver circuit which allows precise control of the ripples on the water.
The final part of the project was fixing the lasers to a special lens scavenged from a projector, and hooking everything up to the driver circuit for the lasers. From there, the caustic patterns can be produced and controlled, although [Neuromodulator] notes that the effects that this device has on film are quite different from the way the human eye and brain perceive them in real life. If you’re fascinated by the effect, even through the lens of the camera, there are other light-based art installations that might catch your eye as well.
What if I told you that you can get rid of your headphones and still listen to music privately, just by shooting lasers at your ears?
The trick here is something called the photoacoustic effect. When certain materials absorb light — or any electromagnetic radiation — that is either pulsed or modulated in intensity, the material will give off a sound. Sometimes not much of a sound, but a sound. This effect is useful for spectroscopy, biomedical imaging, and the study of photosynthesis. MIT researchers are using this effect to beam sound directly into people’s ears. It could lead to devices that deliver an audio message to specific people with no hardware on the receiving end. But for now, ditching those AirPods for LaserPods remains science fiction.
There are a few mechanisms that explain the photoacoustic effect, but the simple explanation is the energy causes localized heating and cooling, the material microscopically expands and contracts, and that causes pressure changes in the sample and the surrounding air. Saying pressure waves in air is just a fancy way of explaining sound.
Lightsabers have enchanted audiences since their appearance in the very first Star Wars film in 1977. Unfortunately, George Lucas hasn’t shared the technology in the years since then with the broader public, so we’re left to subsist on pale imitations. This is just such a build.
The closest human analog to Jedi technology is the laser, and this build uses 8 of them in combination with two LEDs. They’re aimed to coincide at a fixed distance above the hilt. A CO2 bicycle inflater is then used to blow through an e-cigarette to create a fog. This makes the red lasers readily visible to the human eye.
This ersatz lightsaber does have its limitations – fast motion tends to scatter the fog, making it once again invisible, and it’s really at its best held in a vertical orientation. There’s also some divergence beyond the focused point. With that said, it does look somewhat impressive when held still, smouldering away.
The harp is an ancient instrument, but in its current form, it seems so unwieldy that it’s a wonder that anyone ever learns to play it. It’s one thing to tote a rented trumpet or clarinet home from school to practice, but a concert harp is a real pain to transport safely. The image below is unrelated to the laser harp project, but proves that portable harping is begging for some good hacks.
Enter this laser harp, another semester project from [Bruce Land]’s microcontroller course at Cornell. By replacing strings with lasers aimed at phototransistors, [Glenna] and [Alex] were able to create a more manageable instrument that can be played in a similar manner. The “strings” are “plucked” with the fingers, which blocks the laser light and creates the notes.
But these aren’t just any old microcontroller-generated sounds. Rather than simply generating a tone or controlling a synthesizer, the PIC32 uses the Karplus-Strong algorithm to model the vibration of a plucked string. The result is very realistic, with all the harmonics you’d expect to hear from a plucked string. [Alex] does a decent job putting the harp through its paces in the video below, and the write-up is top notch too.
Lumia was once used to refer to a broad swathe of artistic lighting, but these days, more commonly refers to effects that create an aurora-like appearance, as one would see near the poles of our fine Earth. [Adam] first covers the history of the effect, as pioneered by Thomas Wilfred with the Clavilux in the early part of the 20th Century.
The video then covers the basics of creating lumia effects using DIY methods. The key is to combine slow rotation with an organically deformed refractive medium. [Adam]’s rig of choice is a basic laser projector, rotating at just 1/3 of a rotation per minute. This is then combined with a variety of homebrewed refractive media – torture tubes made from glass, acrylic sheets coated with muddled epoxy, and even a crumpled water bottle.
It’s an excellent primer on how to get started with lumia, and [Adam] covers a wide variety of tips and tricks as well as potential pitfalls to avoid.
We see plenty of great lighting projects around these parts – check out the Kinetic Chandelier. Video after the break.
When we think of physics experiments, we tend to envision cavernous rooms filled with things like optical benches, huge coils in vacuum chambers, and rack after rack of amplifiers and data acquisition hardware. But it doesn’t have to be that way – you can actually perform laser interferometry with a single component and measure sub-micron displacements and more.
The astute viewer of [Ben Krasnow]’s video below will note that in order to use the one component, a laser diode, as an interferometer, he needed a whole bunch of support gear, like power supplies, a signal generator, and a really, really nice mixed-signal oscilloscope. But the principle of the experiment is the important bit, which uses a laser diode with a built-in monitoring photodiode. Brought out to a third lead, older laser diodes often used these photodiodes to control the light emitted by the laser junction. But they also respond to light reflected back into the laser diode, and thanks to constructive and destructive interference, can actually generate a signal that corresponds to very slight displacements of a reflector. [Ben] used it to measure the vibrations of a small speaker, the rotation of a motor shaft, and with a slight change in setup, to measure the range to a fixed target with sub-micron precision. It’s fascinating stuff, and the fact you can extract so much information from a single component is pretty cool.
We really like [Ben]’s style of presentation, and the interesting little nooks and crannies of physics that he finds a way to explore. He recently looked at how helium can kill a MEMS sensor, an equally fascinating topic.
Laser engraving and cutting has something in common with focusing the sun’s rays with a magnifying glass: good focus is critical to results. If materials of varying thicknesses are used, focus needs to be re-set every time the material changes, and manual focusing quickly becomes a chore. [Scorch Works] has a clever solution to avoid constant re-focusing that doesn’t involve sensors or motors of any sort. The result is a self-adjusting bed that compensates for material height changes, ensuring that the top surface of the material is always a fixed distance from the laser’s head.
The way [Scorch Works] has done this is to make two spring-loaded clamps from angle aluminum and a few pieces of hardware. When a sheet of material is placed into the machine, the edges get tucked underneath the aluminum “lips” while being pushed upward from beneath. By fixing the height of the top layer of angle aluminum, any sheet stock always ends up the same distance from the laser head regardless of the material’s thickness.
[Scorch Works] shows the assembly in action in the video embedded below, along with a few different ways to accommodate different materials and special cases, so be sure to check it out.