[Brainiac75] is a fan of fiber optic lamps, except for one thing—they’re often remarkably dim. Thus, they set out to hack the technology to deliver terrifying amounts of light while still retaining their quirky charm.

Older fiber optic lamps use a dim filament lamp or halogen lamp to light them up. They also often feature a spinning color disk to vary the light patterns, which does have the side effect of absorbing some of the already-limited light output.

When it came to upgrading his own decades-old lamp, [Braniac75] decided to initially stick within the specs of the original halogen lamp. The fixture was rated for 12 volts at 5 watts, with a GU4/GZ4 compatible base, and white light was desired so the color wheel could still do its thing.  Swapping out the original 5 W halogen for a 2.5 W LED unit brought a big upgrade in brightness, since the latter is roughly equivalent to a 20 W halogen in light output. Upgrading to a 4.2 W LED pushed things even further, greatly improving the look of the lamp.

The video also explores modding a modern fiber optic lamp, too. It was incredibly cheap, running off batteries and using a single color-changing LED to illuminate the fibers. [Braniac75] decided to try illuminating the plastic fibers with an RGB stage lighting laser rig—namely, the LaserCube Ultra 7.5 W from Wicked Lasers. With this kind of juice, the fiber lamp is eye-searingly bright, quite literally, and difficult to film. However, with the laser output dialed way down, the lamp looks amazing—with rich saturated colors dancing across the fiber bundle as the lasers do their thing.

If you’ve ever wanted to build a fiber lamp that doesn’t look like a cheap gimmick, now you know how. We’ve looked at weird applications for these lamps before, too.

When we first heard the term “random laser,” we did a double-take. After all, most ordinary sources of light are random. One defining characteristic of a traditional laser is that it emits coherent light. By coherent, in this context, that usually includes temporal coherence and spatial coherence. It is anything but random. It turns out, though, that random laser is a bit of a misnomer. The random part of the name refers to how the device generates the laser emission. It is true that random lasers may produce output that is not coherent over long time scales or between different emission points, but individually, the outputs are coherent. In other words, locally coherent, but not always globally so.

That is to say that a random laser might emit light from four different areas for a few brief moments. A particular emission will be coherent. But not all the areas may be coherent with respect to each other. The same thing happens over time. The output now may not be coherent with the output in a few seconds.

Baseline

A conventional laser works by forming a mirrored cavity, including a mirror that is only partially reflective. Pumping energy into the gain medium — the gas, semiconductor, or whatever — produces more photons that further stimulate emission. Only cavity modes that satisfy the design resonance conditions and experience gain persist, allowing them to escape through the partially reflecting mirror.

The laser generates many photons, but the cavity and gain medium favor only a narrow set of modes. This results in a beam that is of a very narrow band of frequencies, and the photons are highly collimated. Sure, they can spread over a long distance, but they don’t spread out in all directions like an ordinary light source.

So, How does a Random Laser Work?

Random lasers also depend on gain, but they have no mirrors. Instead, the gain medium is within or contains some material that highly scatters photons. For example, rough crystals or nanoparticles may act as scattering media to form random lasers.

The scattering has photons bounce around at random. Some of the photons will follow long paths, and if the gain exceeds the losses along those paths, laser emission occurs. Incoherent random lasers that use powder (to scatter) or a dye (as gain medium) tend to have broadband output. However, coherent random lasers produce sharp spectral lines much like a conventional laser. They are, though, more difficult to design and control.

Random lasers are relatively new, but they are very simple to construct. Since the whole thing depends on randomness, defects are rarely fatal. The downside is that it is difficult to predict exactly what they will emit.

There are some practical use cases, including speckle-free illumination or creating light sources with specific fingerprints for identification.

It’s Alive!

Biological tissue often can provide scattering for random lasers. Researchers have used peacock feathers, for example. Attempts to make cells emit laser light are often motivated by their use as cellular tags or to monitor changes in the laser light to infer changes in the cell itself.

The video below isn’t clearly using a random laser, but it gives a good overview of why researchers want your cells to emit laser light.

You may be thinking: “Isn’t this just amplified spontaneous emission?” While random lasers can resemble amplified spontaneous emission (ASE), true random lasing exhibits a distinct turn-on threshold and, in some cases, well-defined spectral modes. ASE will exhibit a smooth increase in output as the pump energy increases. A random laser will look like ASE until you reach a threshold pump energy. Then a sharp rise will occur as the laser modes suddenly dominate.

We glossed over a lot about conventional lasers, population inversion, and related topics. If you want to know more, we can help.

We suspect there are three kinds of people in the world. People who have access to a Michelson Interferometer and are glad, those who don’t have one and don’t know what one is, and a very small number of people who want one but don’t have one. But since [Longest Path Search] built one using 3D printing, maybe the third group will dwindle down to nothing.

If you are in the second camp, a Michelson interferometer is a device for measuring very small changes in the length of optical paths (oversimplifying, a distance). It does this by splitting a laser into two parts. One part reflects off a mirror at a fixed distance from the splitter. The other reflects off another, often movable, mirror. The beam splitter also recombines the two beams when they reflect back, producing an interference pattern that varies with differences in the path length between the splitter and the mirror. For example, if the air between the splitter and one mirror changes temperature, the change in the refraction index will cause a minute difference in the beam, which will show up using this instrument.

The device has been used to detect gravitational waves, study the sun and the upper atmosphere, and also helped disprove the theory that light is transmitted through a medium known as luminiferous aether.

The tolerances for such a device are tight, but within the capability of modern 3D printers. The CAD files are online. The key was the mirror mounts, which use springs and thumbscrews. So you do need some hardware and, oh yeah, a laser, although that’s not as hard to obtain as it once was. You obviously can’t 3D print the mirrors or the beam splitter either.

The post claims the device is cheap because the bill of materials was roughly $3, although that didn’t include the beamsplitter, which would bring the cost up to maybe $20. The device, in theory, could detect distance changes as small as one wavelength of the laser, which is around 650nm. Not bad for a few bucks.

Not all Michelsons use lasers. The man behind the Michelson instrument also worked out how to do Fourier analysis with a mechanical computer.

You can hear sound, of course, but what if you could see it with a laser? That’s what [Goosetopherson] thought about, and thus a new project that you can see in the video below was born.

The heart of the project is an I2S chip and an ESP32. Sound energy deforms a plastic film that causes a mirror to move. The moving mirror alters the course of the laser’s beam.

An important part of the project is the 3D printed enclosure designed in Fusion. Some wires are routed through during printing, and there are heat-set inserts.

If you haven’t run into it before, you can think of I2S as I2C for stereo audio. It uses a synchronous protocol to push audio data using three wires. The board in question takes the digital data and decodes it to drive the speaker.

This is a simple project that would lend itself to lots of substitutions if you decide to replicate it. In fact, we’ve seen a version of this that is nothing more than a Bluetooth speaker, some plastic film, a mirror, and a laser.