Science

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A vertically-mounted black disk with a concentric pattern of reflective disks is illuminated under a red light. A large number of copper wires run away from the the disk to a breadboard.

Deforming A Mirror For Adaptive Optics

October 13, 2025 by 16 Comments

As frustrating as having an atmosphere can be for physicists, it’s just as bad for astronomers, who have to deal with clouds, atmospheric absorption of certain wavelengths, and other irritations. One of the less obvious effects is the distortion caused by air at different temperatures turbulently mixing. To correct for this, some larger observatories use a laser to create an artificial star in the upper atmosphere, observe how this appears distorted, then use shape-changing mirrors to correct the aberration. The physical heart of such a system is a deformable mirror, the component which [Huygens Optics] made in his latest video.

The deformable mirror is made out of a rigid backplate with an array of linear actuators between it and the thin sheet of quartz glass, which forms the mirror’s face. Glass might seem too rigid to flex under the tenth of a Newton that the actuators could apply, but everything is flexible when you can measure precisely enough. Under an interferometer, the glass visibly flexed when squeezed by hand, and the actuators created enough deformation for optical purposes. The actuators are made out of copper wire coils beneath magnets glued to the glass face, so that by varying the polarity and strength of current through the coils, they can push and pull the mirror with adjustable force. Flexible silicone pillars run through the centers of the coils and hold each magnet to the backplate.

A square wave driven across one of the actuators made the mirror act like a speaker and produce an audible tone, so they were clearly capable of deforming the mirror, but a Fizeau interferometer gave more quantitative measurements. The first iteration clearly worked, and could alter the concavity, tilt, and coma of an incoming light wavefront, but adjacent actuators would cancel each other out if they acted in opposite directions. To give him more control, [Huygens Optics] replaced the glass frontplate with a thinner sheet of glass-ceramic, such as he’s used before, which let actuators oppose their neighbors and shape the mirror in more complex ways. For example, the center of the mirror could have a convex shape, while the rest was concave.

This isn’t [Huygens Optics]’s first time building a deformable mirror, but this is a significant step forward in precision. If you don’t need such high precision, you can also use controlled thermal expansion to shape a mirror. If, on the other hand, you take it to the higher-performance extreme, you can take very high-resolution pictures of the sun.

Tubeless X-Ray Runs On Patience

October 12, 2025 by 9 Comments

Every time we check in on [Project326], he’s doing something different with X-rays. This week, he has a passive X-ray imager. On paper, it looks great. No special tube is required and no high voltage needed. Actually, no voltage is needed at all. Of course, there’s no free lunch. What it does take is a long time to produce an image.

While working on the “easy peasy X-ray machine,” dental X-ray film worked well for imaging with a weak X-ray source. He found that the film would also detect exposure to americium 241. So technically, not an X-ray in the strictest sense, but a radioactive image that uses gamma rays to expose the film. But to normal people, a picture of the inside of something is an X-ray even when it isn’t.

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A magnifying glass is seen behind a small tea candle. The magnifying image is projecting the shadow of a column of heated air.

Finding Simpler Schlieren Imaging Systems

October 6, 2025 by 3 Comments

Perhaps the most surprising thing about shadowgraphs is how simple they are: you simply take a point source of light, pass the light through a the volume of air to be imaged, and record the pattern projected on a screen; as light passes through the transition between areas with different refractive indices, it gets bent in a different direction, creating shadows on the viewing screen. [Degree of Freedom] started with these simple shadowgraphs, moved on to the more advanced schlieren photography, and eventually came up with a technique sensitive enough to register the body heat from his hand.

The most basic component in a shadowgraph is a point light source, such as the sun, which in experiments was enough to project the image of an escaping stream of butane onto a sheet of white paper. Better point sources make the imaging work over a wider range of distances from the source and projection screen, and a magnifying lens makes the image brighter and sharper, but smaller. To move from shadowgraphy to schlieren imaging, [Degree of Freedom] positioned a razor blade in the focal plane of the magnifying lens, so that it cut off light refracted by air disturbances, making their shadows darker. Interestingly, if the light source is small and point-like enough, adding the razor blade makes almost no difference in contrast.

With this basic setup under his belt, [Degree of Freedom] moved on to more unique schlieren setups. One of these replaced the magnifying lens with a standard camera lens in which the aperture diaphragm replaced the razor blade, and another replaced the light source and razor with a high-contrast black-and-white pattern on a screen. The most sensitive technique was what he called double-pinhole schlieren photography, which used a pinhole for the light source and another pinhole in place of the razor blade. This could image the heated air rising from his hand, even at room temperature.

The high-contrast background imaging system is reminiscent of this technique, which uses a camera and a known background to compute schlieren images. If you’re interested in a more detailed look, we’ve covered schlieren photography in depth before.

Thanks to [kooshi] for the tip!

A man is shown behind a table, on which a glass apparatus like a distillation apparatus is set, with outlets leading into a large container in the center of the table, and from there to a pump.

Pulling A High Vacuum With Boiling Mercury

October 3, 2025 by 21 Comments

If you need to create a high vacuum, there are basically two options: turbomolecular pumps and diffusion pumps. Turbomolecular pumps require rotors spinning at many thousands of rotations per minute and must be carefully balanced to avoid a violent self-disassembly, but diffusion pumps aren’t without danger either, particularly if, like [Advanced Tinkering], you use mercury as your working fluid. Between the high vacuum, boiling mercury, and the previous two being contained in fragile glassware, this is a project that takes steady nerves to attempt – and could considerably unsteady those nerves if something were to go wrong.

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The 19th Century Quantum Mechanics

September 26, 2025 by 18 Comments

While William Rowan Hamilton isn’t a household name like, say, Einstein or Hawking, he might have been. It turns out the Irish mathematician almost stumbled on quantum theory in the or around 1827. [Robyn Arianrhod] has the story in a post on The Conversation.

Famously, Newton worked out the rules for the motion of ordinary objects back in 1687. People like Euler and Lagrange kept improving on the ideas of what we call Newtonian physics. Hamilton produced an especially useful improvement by treating light rays and moving particles the same.

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Set Phone To… Hyperspectral

September 26, 2025 by 24 Comments

While our eyes are miraculous little devices, they aren’t very sensitive outside of the normal old red, green, and blue spectra. The camera in your phone is far more sensitive, and scientists want to use those sensors in place of expensive hyperspectral ones. Researchers at Purdue have a cunning plan: use a calibration card.

The idea is to take a snap of the special card and use it to understand the camera’s exact response to different colors in the current lighting conditions. Once calibrated to the card, they can detect differences as small as 1.6 nanometers in light wavelengths. That’s on par with commercial hyperspectral sensors, according to the post.

You may wonder why you would care. Sensors like this are useful for medical diagnostic equipment, analysis of artwork, monitoring air quality, and more. Apparently, high-end whisky has a distinctive color profile, so you can now use your phone to tell if you are getting the cheap stuff or not.

We also imagine you might find a use for this in phone-based spectrometers. There is plenty to see in the hyperspectral world.