Growing Simple Crystals For Non-Linear Optics Experiments

July 6, 2023 by 18 Comments

Here’s an exercise for you: type “crystals” into your favorite search engine and see what you get. If you’re anything like us, you’ll get a bunch of pseudoscientific posts about the healing power of crystals, along with offers to buy the same at exorbitant prices. But woo-woo aside, certain crystals do have seemingly magical powers — like the ability to turn light from one color into another.

None of this is magic, of course. Rather, as optics aficionado [Les Wright] explains, non-linear optics is all about physics. Big physics, too, like the kind that made the National Ignition Facility the first fusion research outfit to reach the “break-even” point, at least in terms of optical energy. To do so, they need to convert megajoules of infrared laser beams all the way across the visible spectrum into the ultraviolet, relying on huge crystals of deuterated potassium dihydrogen phosphate (KDP) to do so. Depending on how they’re cut, crystals of these sorts have non-linear optical properties like second-harmonic generation, which combines two input photons into a single output photon with twice the energy of the original. This results in a halving of the wavelength of the input, which doubles the frequency.

While the process used at the NIF produces crystals of enormous proportions, [Les] has more modest needs and thus a simpler process. His KDP is an off-the-shelf chemical, nothing fancy about it, which is added to boiling water to make a saturated solution. A little of the solution is poured out into a watch glass to make seed crystals, and everything is allowed to cool slowly. A nice seed crystal is glued to a piece of monofilament fishing line and suspended in the saturated solution, and with enough time a good-sized crystal forms. Placed into the beam path of a 1,064 nm IR laser and rotated carefully relative to the beam, the crystal easily produces a brilliant green laser output.

This is fascinating stuff, and we’re looking forward to seeing where [Les] goes with this. Polishing the crystals to make them optically cleaner would be a good next step, as would perhaps growing even larger crystals.

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ITER Dreams And The Practical Reality Of Making Nuclear Fusion Work On Earth

July 6, 2023 by 52 Comments

Doing something for the first time is tough. Yet to replicate the nuclear fusion process that powers the very stars, and do it right here on Earth in a controlled and sustained fashion is decidedly at the top of the list of ‘tough’ first times. What further complicates matters is when in order to even get to this ‘first’ you also add in a massive, international construction project and a heaping of geopolitics, all of which is a far cry from past nuclear fusion experiments.

With the International Thermonuclear Experimental Reactor (ITER) as the most visible part of nuclear fusion research, it is perhaps little wonder that the recent string of delays and budget increases is leading some to proclaim doom and gloom over the entire sector. This ironically in contrast with the recent news from the US’s NIF and its laser-based inertial confinement fusion, which is both state-funded and will never produce commercial power.

In light of this, it feels pertinent to ask the question of whether ITER is the proverbial white elephant, or even the mausoleum of international science that a recent article in Scientific American makes it out to be. Is fusion research truly doomed to peter out amidst the seemingly never-ending work on ITER?

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It’s A Humble ‘Scope, But It Changed Our World

July 6, 2023 by 45 Comments

A few years ago on a long flight across the North Atlantic, the perfect choice for a good read was iWoz, the autobiographical account of [Steve Wozniak]’s life. In it, he described his work replicating the wildly successful Pong video game and then that of designing the 8-bit Apple computers. A memorable passage involves his development of the Apple II’s color generation circuitry, which exploited some of the artifacts of the NTSC color system to produce a color display in a far simpler manner than might be expected. Now anyone seeking a connection with both Pong and the Apple II can have one of their very own if they have enough money because [Al Alcorn]’s Tektronix 465 oscilloscope is for sale. He’s the designer of the original Pong and used the instrument in its genesis, and then a few years later, he lent it to [Woz] for his work on the Apple II.

This may be the first time Hackaday has featured something from the catalogue of a rare book specialist, but if we’re being honest, for $135,000, it’s a little beyond the reach of a Hackaday scribe. The Tek 465 was a 100 MHz dual-trace model manufactured from 1972 to the early 1980s and, in its day, would have been a very desirable instrument indeed. This one is in pretty good condition with accompanying leads and manual and comes with a letter of authenticity and a hand-written annotation from [Al] himself on its underside. It can be seen up close in the video below the break.

As a ‘scope it’s an instrument many of us would still find useful today, but as the instrument which set in motion not one but two of the seminal moments of our craft, its historical importance can’t be overstated. We hope it will find its way into a museum or similar place where the story of those two developments can be told and that [Al] profits handsomely from its sale.

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Miners Vs NASA: It’s A Nevada Showdown

July 6, 2023 by 74 Comments

Mining projects are approved or disapproved based on all kinds of reasons. There are economic concerns, logistical matters, and environmental considerations to be made. Mining operations can be highly polluting, or they can have outsized effects on a given area by sheer virtue of the material they remove or the byproducts they leave behind.

For a proposed lithium mining operation north of Las Vegas, though, an altogether stranger objection has arisen. NASA has been using the plot of land as a calibration tool, and it doesn’t want any upstart miners messing with its work. 

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This Block Of Rubber Can Count To Ten

July 6, 2023 by 19 Comments

Complex behaviors can arise from simple mechanics, and that’s demonstrated by a block of rubber that acts as a counter.

The block contains beams, and by controlling how the block is compressed, the vertical beams shift in a stable and consistent way, acting as a mechanical counter. It’s a straightforward implementation of the work of two physicists from the Netherlands: [Martin van Hecke] and [Lennard Kwakernaak].

This device brings flexures to mind, which are also examples of obtaining complex and useful behavior from seemingly simple objects. We’ve seen flexures used as latches and counters, and we’ve seen 3D printed flexures as a kind of linear actuator.

You can check out the research paper for more details on the rubber beam counter. [Kwakernaak] aims to create a much more complex structure with elements that interact across a plane instead of in a single direction. Such a device would, in effect, be a simple computer.

Watch the beam counter in action in the short video embedded below. See how the elements of the green rubber block move while constrained by an outer frame that helps control the force that is applied. The thin beams flip from left to right, one at a time with each press.

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Tentacle Robot Is Like An Elephant Trunk

July 6, 2023 by 1 Comment

It sounds like bad science fiction or anime, but researchers are creating helical-artificial fibrous muscle structured tubular soft actuators. What? Oh, tentacle robot arms. Got it.

The researchers at Westlake University in China found inspiration in elephant trunks. Elephant trunks are entirely devoid of bone but use a tubular muscle structure. By deforming certain muscles, complex motion is possible. After understanding how they work, it was just a matter of making a similar structure from artificial muscle fibers.

The resulting actuator uses smart materials and has eleven different morphing modes — more than other attempts to build similar structures. The fabrication sounds difficult, it involves stretching chemically reactive materials over a form with specific winding angles.

The fibers react to light. Depending on the configuration, the stalk can seek light or avoid light. We were hoping the “Materials and Methods” section would give some ideas of how to do this ourselves, but it looks like you’d need some uncommon liquid crystal materials, and you’d also have to work out some of the details.

Animatronic tentacles are usually complex cable affairs. However, we have seen some soft robots in the past, too.

System Essentially Contradicting American Methods

July 5, 2023 by 36 Comments

Today, acronyms such as PAL and initialisms such as NTSC are used as a lazy shorthand for 625 and 525-line video signals, but back in the days of analogue TV broadcasting they were much more than that, indeed much more than simply colour encoding schemes. They became political statements of technological prowess as nations vied with each other to demonstrate that they could provide their citizens with something essentially home-grown. In France, there was the daddy of all televisual symbols of national pride, as their SECAM system was like nothing else. [Matt’s TV Barn] took a deep dive into video standards to find out about it with an impressive rack of test pattern generation equipment.

At its simplest, a video signal consists of the black-and-while, or luminance, information to make a monochrome picture, along with a set of line and frame sync pulses. It becomes a composite video signal with the addition of a colour subcarrier at a frequency carefully selected to fall between harmonics of the line frequency and modulated in some form with the colour, or chrominance, information. In this instance, PAL is a natural progression from NTSC, having a colour subcarrier that’s amplitude modulated and with some nifty tricks using a delay line to cancel out colour shifting due to phase errors.

SECAM has the same line and frame frequency as PAL, but its colour subcarrier is frequency modulated instead of amplitude modulated. It completely avoids the NTSC and PAL phase errors by not being susceptible to them, at the cost of a more complex decoder in which the previous line’s colour information must be stored in a delay line to complete the decoding process. Any video processing equipment must also, by necessity, be more complex, something that provided the genesis of the SCART audiovisual connector standard as manufacturers opted for RGB interconnects instead. It’s even more unexpected at the transmission end, for unlike PAL or NTSC, the colour subcarrier is never absent, and to make things more French, it inverted the video modulation found in competing standards.

The video below takes us deep into the system and is well worth a watch. Meanwhile, if you fancy a further wallow in Gallic technology, peer inside a Minitel terminal.

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