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.
Similar approach is used in toilet factories to ensure water swirls in the right direction when flushed (according to Coriolis Effect).
If the Coriolis Effect worked on scales as small as your toilet bowl, you wouldn’t be able to stand up due to the fluid spinning around in your inner ear.
The size of your inner ear is about 60x smaller than average toilet bowl in the US so it’s obvious that due to effects of the scale, the physics in your body will not match those occuring inside a toilet. In addition, unlike toilets, humans continuously balance to mitigate effects of gravity and lateral acceleration.
Nonetheless the original post is, I guess the technical term is “wrong”.
Tom Clancy taught us all about this decades ago. The password is “nutation”.
I can’t edit but if I could I would point out that “the physics in your body will not match those occuring inside a toilet” is also wrong.
Can you prove it? Of course physics are different depending on macro or micro scale. For example you can only create capilary action in micro scale (like your ear). If you could recreate capilary action in a toilet there would be no need to flush, poop would get sucked into the sewer all by itself.
Physics don’t change unless you reach quantum scales.
But perhaps we would have evolved to to normalise it and used it sense latitude, coupled with the suns position the approximate location on the globe.
:-D This reminds me of posts I’ve read over the years stating that toilet bowls and bathtubs are too small for the Coriolis effect to determine which way water swirls when going down the drain. For whatever reason, the claims didn’t stand up to our limited experimental observations after moving from the US to Oz, where the draining bath swirled the opposite direction from what we had observed in HI.
It comes down to the how the water is injected into the bowl, ie toilet design.
I am hopeful that similar techniques could be used (albeit with significant adaptation) in all-optical radio access networks in mobile systems. It could potentially be the single largest contribution to all optical design (I proposed routing / switching algorithms for hierarchical all-optical networks between 2002 – 2005 (I can send you my thesis if you wish)). These need modification / extension but I will apply the Academic Part of my Brain to this problem this afternoon ! – I don’t want to sound over optimistic but it could be incredible …
I recall the aborted Airborne Laser project used adaptive optics to focus its laser beam over long distances.
https://en.wikipedia.org/wiki/Boeing_YAL-1
First Google X balloons used AO for laser comms, now in a terrestrial point to point system under a new company that can do gigabits per second through free air (FSO). Would it be appropriate to start calling it FSAO?
Ps: about 9 months ago I read / examined Christiaan Huygens ‘Treatise of Light’ !!
For small telescopes, less than 30 in, we had some great products in the 90s and 2000s. By SBIG. Santa Barbara instrument group.. these use the single mirror, and to actuators. Unfortunately I haven’t seen any AO devices for small telescopes since they went out of business. If you’re lucky you can still find one on cloudynights.com.
I wish we had something like flexible mirrors for small telescopes. But unfortunately the math just doesn’t work at that size.
From what I understand (as an admitted amateur scientist) the deformable mirror is perhaps the easy part–the aberrations caused by the atmosphere still have to be sensed, processed and fed to the actuators. Setting aside the artificial star approach (lasers, pew pew!) the only simple approach I am aware of is to use the input from a star fairly close to what one is viewing.
I have recently finished a telescope built around a 17.5″ (440mm) mirror, and while I am impressed at it’s light gathering capabilities, my higher powered eyepieces really bring out the limitations the atmosphere imposes. Stars become boiling scrambled halos of light. I’ve only had one outing when stars started to resemble points at higher powers, and it so happened it was during a full moon :/