laser

496 Articles

More Mirrors (and A Little Audio) Mean More Laser Power

April 24, 2024 by 10 Comments

Lasers are pretty much magic — it’s all done with mirrors. Not every laser, of course, but in the 1980s, the most common lasers in commercial applications were probably the helium-neon laser, which used a couple of mirrors on the end of a chamber filled with gas and a high-voltage discharge to produce a wonderful red-orange beam.

The trouble is, most of the optical power gets left in the tube, with only about 1% breaking free. Luckily, there are ways around this, as [Les Wright] demonstrates with this external passive cavity laser. The guts of the demo below come from [Les]’ earlier teardown of an 80s-era laser particle counter, a well-made instrument powered by a He-Ne laser that was still in fine fettle if a bit anemic in terms of optical power.

[Les] dives into the physics of the problem as well as the original patents from the particle counter manufacturer, which describe a “stabilized external passive cavity.” That’s a pretty fancy name for something remarkably simple: a third mirror mounted to a loudspeaker and placed in the output path of the He-Ne laser. When the speaker is driven by an audio frequency signal, the mirror moves in and out along the axis of the beam, creating a Doppler shift in the beam reflected back into the He-Ne laser and preventing it from interfering with the lasing in the active cavity. This forms a passive cavity that greatly increases the energy density of the beam compared to the bare He-Ne’s output.

The effect of the passive cavity is plain to see in the video. With the oscillator on, the beam in the passive cavity visibly brightens, and can be easily undone with just the slightest change to the optical path. We’d never have guessed something so simple could make such a difference, but there it is.

Continue reading “More Mirrors (and A Little Audio) Mean More Laser Power” →

Chinese Subs May Be Propelled Silently By Lasers

April 24, 2024 by 57 Comments

If sharks with lasers on their heads weren’t bad enough, now China is working on submarines with lasers on their butts. At least, that’s what this report in the South China Morning Post claims, anyway.

According to the report, two-megawatt lasers are directed through fiber-optic cables on the surface of the submarine, vaporizing seawater and creating super-cavitation bubbles, which reduce drag on the submarine. The report describes it as an “underwater fiber laser-induced plasma detonation wave propulsion” system and claims that the system could generate up to 70,000 newtons of thrust, more than one of the turbofan engines on a 747.

The report (this proxy can get around the paywall) claims that the key to the system are the tiny metal spheres that direct the force of the cavitation implosion to propel the submarine. Similar to a magnetohydrodynamic drive (MHD), there’s no moving parts to make noise. Such a technology has the potential to make China’s submarines far harder to detect.

Looking for more details, we traced the report back to the original paper written by several people at Harbin Engineering University, entitled “Study on nanosecond pulse laser propulsion microspheres based on a tapered optical fiber in water environment“, but it’s still a pre-print. If you can get access to the full paper, feel free to chime in — we’d love to know if this seems like a real prospect or just exaggerated reporting by the local propaganda media.

[Image via Wikimedia Commons]

Optical Tweezers Investigate Tiny Particles

April 22, 2024 by 1 Comment

No matter how small you make a pair of tweezers, there will always be things that tweezers aren’t great at handling. Among those are various fluids, and especially aerosolized droplets, which can’t be easily picked apart and examined by a blunt tool like tweezers. For that you’ll want to reach for a specialized tool like this laser-based tool which can illuminate and manipulate tiny droplets and other particles.

[Janis]’s optical tweezers use both a 170 milliwatt laser from a DVD burner and a second, more powerful half-watt blue laser. Using these lasers a mist of fine particles, in this case glycerol, can be investigated for particle size among other physical characteristics. First, he looks for a location in a test tube where movement of the particles from convective heating the chimney effect is minimized. Once a favorable location is found, a specific particle can be trapped by the laser and will exhibit diffraction rings, or a scattering of the laser light in a specific way which can provide more information about the trapped particle.

Admittedly this is a niche tool that might not get a lot of attention outside of certain interests but for those working with proteins, individual molecules, measuring and studying cells, or, like this project, investigating colloidal particles it can be indispensable. It’s also interesting how one can be built largely from used optical drives, like this laser engraver that uses more than just the laser, or even this scanning laser microscope.

Continue reading “Optical Tweezers Investigate Tiny Particles” →

Fail Of The Week: A Potentially Lethal Tattoo Removal Laser Power Supply

March 24, 2024 by 7 Comments

Caveat emptor is good advice in general, but in the wilds of eBay, being careful with what you buy could be life-saving. To wit, we present [Les Wright]’s teardown and very ginger power-up of an eBay tattoo-removal laser power supply.

Given that [Les] spent all of around $100 on this widowmaker, we’re pretty sure he knew what he was getting himself into. But he likely wasn’t quite prepared for the scale of the sketchiness this thing would exhibit. The deficiencies are almost too many to number, starting with the enclosure, which is not only made completely of plastic but assembled from individual sheets of flat plastic stock that show signs of being glued together by hand. Even the cooling water tank inside the case is pieced together this way, which probably led to the leaks that corroded the PCBs. Another assembly gem is the pair of screws the big energy storage capacitor is jammed under, presumably to hold it in place — because nothing says quality like a BOM that can’t spring for a couple of cable ties. Click through the break to read more and see the video.

Continue reading “Fail Of The Week: A Potentially Lethal Tattoo Removal Laser Power Supply” →

High-Voltage Fun With An Inexpensive Power Supply

March 14, 2024 by 26 Comments

It used to be that nearly every home had at least one decent high-voltage power supply. Of course, it was dedicated to accelerating electrons and slamming them into phosphors so we could bathe ourselves in X-rays (not really) while watching Howdy Doody. These days the trusty tube has been replaced with LEDs and liquid crystals, which is a shame because there’s so much fun to be had with tens of thousands of volts at your disposal.

That’s the impetus behind this inexpensive high-voltage power supply by [Sebastian] over at Baltic Labs. The heavy lifting for this build is done by a commercially available power supply for a 50-watt CO2 laser tube, manufactured — or at least branded — by VEVOR, a company that seems intent on becoming the “Harbor Freight of everything.” It’s a bold choice given the brand’s somewhat questionable reputation for quality, but the build quality on the supply seems decent, at least from the outside. [Sebastian] mounted the supply inside a rack-mount case, as one does, and provided some basic controls, including the obligatory scary-looking toggle switch with safety cover. A pair of ammeters show current and voltage, the latter with the help of a high-voltage resistor rated at 1 gigaohm (!). The high-voltage feedthrough on the front panel is a little dodgy — a simple rubber grommet — but along with the insulation on the high-voltage output lead, it seems to be enough.

The power supply’s 30 kV output is plenty for [Sebastian]’s current needs, which from the video below appear to mainly include spark gap experiments. He does mention that 50 kV commercial supplies are available too, but it would be tough to do that for the $150 or so he spent on this one. There are other ways to go, of course — [Niklas] over at Advanced Tinkering recently shared his design for a more scratch-built high-voltage supply that’s pretty cool too. Whatever you do, though, be careful; we’ve been bitten by a 50 kV flyback supply before and it’s no joke.

Continue reading “High-Voltage Fun With An Inexpensive Power Supply” →

This Unique Flip-Flop Uses Chemistry And Lasers

January 24, 2024 by 8 Comments

One of the first logic circuits most of us learn about is the humble flip-flop. They’re easy enough to build with just a couple of NOR or NAND gates, and even building one up from discrete components isn’t too much of a chore. But building a flip-flop from chemicals and lasers is another thing entirely.

That’s the path [Markus Bindhammer] took for his photochromic molecular switch. We suspect this is less of an attempt at a practical optical logic component and more of a demonstration project, but either way, it’s pretty cool. Photochromism is the property by which molecules reversibly rearrange themselves and change color upon exposure to light, the most common example being glass that darkens automatically in the sun. This principle can be used to create an optical flip-flop, which [Markus] refers to as an “RS” type but we’re pretty sure he means “SR.”

The electronics for this are pretty simple, with two laser modules and their drivers, a power supply, and an Arduino to run everything. The optics are straightforward as well — a beam splitter that directs the beams from each laser onto the target, which is a glass cuvette filled with a clear epoxy resin mixed with a photochromic chemical. [Markus] chose spiropyran as the pigment, which when bathed in UV light undergoes an intramolecular carbon-oxygen bond breakage that turns it into the dark blue pigment merocyanine. Hitting the spot with a red laser or heating the cuvette causes the C-O bond to reform, fading the blue spot.

The video below shows the intensely blue dot spot developing under UV light and rapidly fading thanks to just the ambient temperature. To make the effect last longer, [Markus] cools the target with a spritz from a CO2 cartridge. We imagine other photochromic chemicals could also be employed here, as could some kind of photometric sensor to read the current state of the flip-flop. Even as it is, though, this is an interesting way to put chemistry and optics to work.

Continue reading “This Unique Flip-Flop Uses Chemistry And Lasers” →

Hackaday Links Column Banner

Hackaday Links: January 14, 2024

January 14, 2024 by 1 Comment

How long does it take a team of rocket scientists to remove two screws? When the screws they’re working on are keeping a priceless sample of asteroid safe, it’s about three months. That’s how long NASA has been working on the OSIRIS-REx sample return canister, which came back to Earth from asteroid Bennu back in September. The container was crammed full of asteroid bits, thanks in part to an overly energetic impact between the sample-collecting boom and Bennu. There was so much stuff that planetary scientists were able to recover about 70 grams of material that was covering the outside of the sealed container; this must have been a boon to the engineers, who got to figure out how to open the jammed cover of the container without anyone breathing down their necks for samples to study. The problem was a pair of stuck fasteners out of the 35 holding the lid on the container; the solution was far more complicated than a spritz of WD-40 and a little bit of heating with an oxy-acetylene torch. Engineers had to design two “clamp-like tools” and test them on a mock-up to make sure they wouldn’t contaminate the sample. We’d love to know more about these tools; trust us, we’ll be looking into this closely. If we find anything, a full article will be forthcoming.

Continue reading “Hackaday Links: January 14, 2024” →