Gentle Introduction To White Light Interferometry

March 13, 2024 by Maya Posch 3 Comments

Screenshot of the Zygo white light interferometry microscope software. (Credit: Huygens Optics)

White light interferometry (WLI) is a contact-free optical method for measuring surface height. It uses the phase difference between the light reflected off a reference mirror and the target sample to calculate the height profile of the sample’s surface. As complex as this sounds, it doesn’t take expensive hardware to build a WLI microscope, as [Huygen Optics] explains in a detailed introductory video on the topic. At its core you need a source of white light (e.g. a white LED), with a way to focus the light so as to get a spatially coherent light source, like aluminium foil with a pin hole and a lens.

This light source then targets a beam splitter, which splits the light into one beam that targets the sample, and one that targets the reference mirror. When both beams are reflected and return to the beam splitter, part of the reflected light from either side ends up at the camera, which captures the result of the reference and sample beams after their interference (i.e. combination of the amplitudes). This creates a Michelson interferometer, which is simple, but quite low resolution. For the demonstrated Zygo Newview 100 WLI microscope this is the first objective used, followed by a more recent innovation: the Mirau interferometer, which integrates the reference mirror in such a manner that much higher resolutions are possible, down to a few µm.

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Fancy Gyroscopes Are Key To Radio-Free Navigation

November 1, 2023 by Lewin Day 49 Comments

Back in the old days, finding out your location on Earth was a pretty involved endeavor. You had to look at stars, use fancy gimballed equipment to track your motion, or simply be able to track your steps really really well. Eventually, GPS would come along and make all that a bit redundant for a lot of use cases. That was all well and good, until it started getting jammed all over the place to frustrate militaries using super-accurate satellite-guided weapons.

Today, there’s a great desire for more accurate navigational methods that don’t require outside communications that can easily be jammed. High-tech gyroscopes have long been a big part of that effort, allowing the construction of inertial navigation systems with greater accuracy than ever before.

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Developing Warp Drive Might Take Antifreeze

February 8, 2023 by Al Williams 63 Comments

In Star Trek, dilithium crystals — whatever those are — are critical to the operation of a starship’s warp drives. But a Texas professor thinks he can make a baby step towards a warp drive using ethylene glycol, which is commonly found in antifreeze.

While superluminal travel has been regarded as impossible for many years, recent work has suggested ways we might be able to circumvent the light-speed barrier. Unfortunately, all of these mathematical theories require energy and types of matter that we don’t know how to create yet. But [Dr. Chance Glen] believes that by shaping the energy in a specific way through a dielectric, the math can work out so that there’s no exotic negative energy required.

The experiment involves shooting RF energy into an antifreeze container and using a laser interferometer to detect gravity waves. Of course, that will involve some very sensitive measurements to account for other tiny perturbations that might give false readings. As we’ve seen in the past, that’s a task easier said than done.

Does this make sense? Beats us. Our physics and math are too out of date to make a good guess about how much of this is real and how much is hype. Of course, if he does detect gravity waves, that will get us as close to warp drive as the invention of the telegraph got us to cell phones. Then again, you have to start somewhere.

If you want to know more about the state of rocket engines, including the nascent possibility of warp drives, we’ve discussed that before. Incidentally, if you think the experiment sounds a bit like the the Laser Interferometer Gravitational-wave Observatory (LIGO), you aren’t wrong.

An Open Source Modular Flexure Construction Set

November 22, 2022 by Dave Rowntree 14 Comments

Flexures are one of those innocent-looking mechanisms that one finds inside practically any kind of consumer device. Providing constrained movements with small displacements, complete with controlled tension, they can be rather tricky to design. GrabCAD designer [Vyacheslav Popov] hails from Ukraine, and due to the current situation there, plans to sell a collection of flexure building blocks became difficult. In the end, [Vyacheslav] decided to generously release his work open source, for all to enjoy. This collection is quite extensive, looking like it could solve a huge variety of flexure design problems. (Links to the first three sets: Set00, Set01, Set02 but check the author’s collection page for many others)

It’s not just those super-cheap mechanisms in throw-away gadgets that leverage flexures, it’s much more. The Mars rovers use flexure-based suspension, scientific instruments (interferometers and the like) make use of them for small motions where specific axis constraints are needed, and finally, MEMS accelerometers and gyroscopes are based entirely upon them. We’re not even going to try to name examples of flexures in the natural world. They’re everywhere. And, now we’ve got some more design examples to use, so why not flex your flexure muscles and send one to the 3D printer and have a play?

We see flexures here quite a bit, like this nice demonstration of achievable accuracy. Flexures can make some delicious mechanisms, and neat 3D printable input devices.

Thanks to [Addison] for the tip!

A Tiny Forest Of Resistors Makes For Quick And Dirty Adaptive Optics

July 25, 2022 by Dan Maloney 16 Comments

The term “adaptive optics” sounds like something that should be really complicated and really expensive. And in general, the ability to control the properties of optical elements is sufficiently difficult enough that it’s reserved for big-science stuff like billion-dollar space telescopes.

But that doesn’t mean there aren’t quick and dirty adaptive optics that are suitable for the budget-minded experimenter, like this thermally deformable mirror. As [Zachary Tong] explains, this project, which started quite some time ago, is dead simple — a 4 by 4 array of through-hole resistors stand on end, and these are attached to a glass coverslip that has been aluminized on one side. An Arduino and a couple of shift registers make it possible to individually address each of the 16 resistors in the array. Passing a current through a resistor heats it up a bit, leading to thermal expansion and a slight deflection of the mirror sitting on top of the array. Controlling which resistors heat up and by how much should lead to deformation of the mirror surface in a predictable way.

The video below shows some of [Zach]’s experiments with the setup. Unfortunately, he wasn’t able to fully demonstrate its potential — the low-quality mirror didn’t cooperate with his homebrew interferometer. He was, however, able to use a dial indicator to show deflection of the mirror in the 2- to 3-micron range by heating the array. That alone is pretty cool, especially given the dirt cheap nature of the build.

As for practical uses, don’t get too excited. As [Zach] points out, thermal systems like this will probably never be as fast as MEMS or piezoelectric actuators, and many use cases for adaptive optics really don’t react well to added heat. But changing the shape of a mirror with air pressure is another thing.

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Keynote Video: Dr. Keith Thorne Explains The Extreme Engineering Of The LIGO Hardware

December 9, 2021 by Mike Szczys 18 Comments

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a huge installation measured in kilometers that is listening for wrinkles in space-time. Pulling this off is a true story of hardware and software hacking, and we were lucky to have Dr. Keith Thorne dive into those details with his newly published “Extreme Instruments for Extreme Astrophysics” keynote from the 2021 Hackaday Remoticon.

Gravity causes space-time to stretch — think back to the diagrams you’ve seen of a massive orb (a star or planet) sitting on a plane with grid lines drawn on it, the fabric of that plane being stretch downward from the mass of the orb. If you have two massive entities like black holes orbiting each other, they give off gravitational waves. When they collide and merge, they create a brief but very strong train of waves. Evidence of these events are what LIGO is looking for.

Rai Weiss had the idea to look for gravitational waves using laser interferometers in about 1967, but the available laser technology was too new to accomplish the feat. In an interferometer, a laser is shot through a beam splitter and one beam reflects out and back over a distance, and is then recombined with the other half using a photodetector to measure the intensity of light. As the distance in the long leg changes, the relative phase of the lasers shift, and the power detected will vary.

LIGO is not your desktop interferometer. It uses a 5 kW laser input. The 4 km legs of the interferometer bounce the light back and forth 1,000 times for an effective 4,000 km travel distance. These legs are kept under extreme vacuum and the mirrors are held exceptionally still. It’s worth it; the instrument can measure at a precision of 1/10,000 the diameter of a proton!

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These First Remoticon Speakers Are Just A Taste Of What’s To Come

October 14, 2021 by Tom Nardi 1 Comment

With the 2021 Hackaday Remoticon fast approaching, we’ve been hard at work crafting a schedule filled with thought-provoking presentations from knowledgeable speakers; precisely what you’ve come to expect from one of our events, virtual or otherwise. We’ve already announced that Laser Interferometer Gravitational-Wave Observatory (LIGO) astrophysicist Keith Thorne will be presenting a literally out-of-this-world keynote on the incredible engineering it takes to detect gravitational waves with the highest precision interferometers ever devised, but that’s only the beginning.

To make doubly sure we’ll be able to pack every available minute of our second Remoticon with fascinating content, we’ve decided to extend the deadline on talk proposals for a few more days to see what the late-bloomers can bring to the table. If you’ve ever wanted to present at a Hackaday event, but couldn’t swing the trip to Pasadena or Belgrade, this is your chance to take the stage virtually and show off what you’re passionate about.

In the meantime, we’ve churned through enough of the early proposals to let slip the first four talks that we’ll be beaming out between November 19th and 20th. There is plenty more to announce over the coming weeks, but hopefully this gives you an idea of what we’ve got in store for our global audience of hardware hackers. So grab your Remoticon ticket right now!

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