The magic mirror behind advanced technology

High on a mountain in Chile’s dry Atacama Desert, the European Southern Observatory (ESO) is building the world’s largest optical telescope.

No time was wasted in choosing a name – it will be called the Extremely Large Telescope, or ELT.

Instead, we have invested enormous effort in designing and building the “world’s largest eye”, which will begin collecting images in 2028 and will likely expand our understanding of the universe.

None of this would be possible without the most advanced mirrors ever created.

Dr Elise Vernet, an expert in adaptive optics at ESO, has been overseeing the development of the five giant mirrors that will collect light and transmit it to the telescope’s measurement equipment.

Each of ELT’s custom mirrors is a feat of optical design.

Dr. Vernet described the 14-foot (4.25-meter) convex M2 mirror as “a work of art.”

But perhaps the M1 and M4 mirrors best exemplify the level of sophistication and precision required.

The primary mirror, M1, is the largest mirror ever built for an optical telescope.

“It is 39 meters [128ft] Diameter, by [798] The hexagonal mirror sections are aligned so that it behaves like a perfect monolithic mirror,” said Dr. Vernet.

The M1 will collect 100 million times more light than the human eye and must be able to maintain position and shape to a level of precision 10,000 times finer than a human hair.

The M4 is the largest deformable mirror ever built and can deform 1,000 times per second to correct for atmospheric turbulence and vibrations in the telescope itself that might otherwise distort images.

Its flexible surface is made up of six petals of glass-ceramic material less than 2 millimeters (0.075 inches) thick.

The petals are made by Schott in Mainz, Germany, and then shipped to engineering firm Safran Reosc outside Paris, where they are polished and assembled into the complete mirror.

All five mirrors are nearly complete and will soon be shipped to Chile for installation.

While these giant mirrors will be used to capture the light of the universe, ESO’s neighbor the Max Planck Institute for Quantum Optics in Garching has invented a quantum mirror that can operate on the tiniest scales imaginable.

In 2020, a research team succeeded in getting a thin film of 200 neatly aligned atoms to collectively reflect light, effectively creating a mirror so small that it is invisible to the naked eye.

In 2023, they successfully placed a microscopically controlled atom at the center of the array, creating a “quantum switch” that can be used to control whether the atom is transparent or reflective.

“Theorists predict, and we observe experimentally, that in these ordered structures, once you absorb a photon, it will be re-emitted, and in fact it is emitted [in one predictable] direction, which is why it acts as a mirror,” said Dr. Pascal Wexer, a postdoctoral researcher at the institute.

This ability to control the direction in which atoms reflect light could be applied to a variety of quantum technologies in the future, such as hacker-proof quantum networks for storing and transmitting information.

Further northwest, in Oberkochen near Stuttgart, Zeiss is making mirrors with another extreme quality.

The optics company spent years developing an ultra-flat mirror that has become a key component of the machines that print computer chips, called extreme ultraviolet lithography, or EUV.

Dutch company ASML is the world’s leading EUV manufacturer, of which Zeiss mirrors are an important component.

Zeiss’s EUV mirrors can reflect very small wavelengths of light, thus achieving image clarity in tiny areas, so that more and more transistors can be printed on the same silicon wafer.

To explain how flat the mirror is, Dr. Frank Lomond, president of Zeiss’ semiconductor manufacturing optics division, used a topographic analogy.

“If you scale up a household mirror to the size of Germany, the highest point would be 5 meters above sea level. [as in the James Webb Space Telescope]i.e. 2 cm [0.75in]“On an EUV mirror, that number is 0.1 millimeter,” he explains.

This ultra-smooth mirror surface, combined with a system that controls the positioning of the mirrors (also made by Zeiss), enables a level of precision equivalent to bouncing light off EUV mirrors on the Earth’s surface and picking out a golf ball on the Moon.

While these mirrors sound extreme, Zeiss has plans to improve them to help make more powerful computer chips.

“We have ideas about how to further develop EUV. By 2030, our goal is to create a microchip with a trillion transistors. Today, we probably already have 100 billion transistors.”

The latest technology from Zeiss brings this goal closer, capable of printing three times more structures in the same area than the current generation of chipmaking machines.

“The semiconductor industry has this dominant and powerful roadmap that provides incentives for all players to contribute to the solution. With this, we have been able to make advances in microchip manufacturing, which has enabled things like artificial intelligence that were unimaginable even a decade ago,” said Dr. Rohmund.

It remains to be seen what humanity will understand and be able to do in a decade, but there is no doubt that mirrors will be at the heart of the technology that will get us there.