How to take a better picture of atom clouds? Mirrors

When it goes online, the MAGIS-100 experiment at the Fermi National Accelerator Laboratory of the Department of Energy and its successors will explore the nature of gravitational waves and research certain kinds of wave-like dark matter. But first, the researchers need to figure out something pretty basic.

But a team from SLAC that included Stanford graduate student Sanha Cheong and Murtaza Safdari, SLAC professor Ariel Schwartzman, and SLAC scientists Michael Kagan, Sean Gasiorowski, Maxime Vandegar, and Joseph Frish have found a simple way to do this: mirrors. By arranging mirrors in a domed configuration around an object, they can reflect more light back to the camera and image multiple sides of an object simultaneously.

And , reports the team in the Journal of Instrumentation, there is an added benefit. Since the camera now gathers views of an object taken from many different angles, the system is an example of “bright field imaging”, which not only captures the intensity of light, but also the path in which the light rays travel. As a result, the mirror system can help researchers build a three-dimensional model of an object, such as a cloud of atoms.

“We are advancing imaging in experiments like MAGIS-100 towards the new imaging paradigm with this system,” said Safdari.

The 100 Meter-Extensive Matter-Wave Atomic Gradiometer Interferometric Sensor, or MAGIS-, is a new type of experiment installed in a vertical shaft at the DOE’s Fermi Countrywide Accelerator Laboratory. Known as the Atomic Interferometer, it will exploit quantum phenomena to detect passing waves of ultralight dark matter and free-falling strontium atoms.

Experimenters will release clouds of strontium atoms in a vacuum tube that spans the length of the shaft, then shine laser light on the falling clouds. Each strontium atom acts like a wave, and the laser light sends each of these atomic waves into a superposition of quantum states, one of which continues on its original path while the other is propelled much higher.

When recombined, the waves create an interference pattern in the strontium atom wave, similar to the complex pattern of ripples that emerges after jumping a rock on a pond. This interference pattern is wise to anything that changes the relative distance between quantum wave pairs or the internal properties of atoms, which could be influenced by the presence of dark matter.

To see interference patterns. which involves a number of challenges. The strontium clouds themselves are small, only about a millimeter in diameter, and the details researchers need to see are about a tenth of a millimeter in diameter. The camera itself must be placed outside a room and looking through a window for a relatively long distance to see the strontium clouds inside.

But the real problem is the light. To illuminate the strontium clouds, the experimenters will shine lasers on the clouds. However, if the laser light is too intense, it can destroy the details scientists want to see. If it is not extreme enough, the light from the clouds will be too weak for the cameras to see.

“You will only collect the amount of light that falls on the lens,” Safdari said, “which isn’t much.”

Mirrors to the rescue

One idea is to use a large aperture, or aperture. but there is a compromise:, where only a narrow slice of the image is leveled.

Another possibility would be to position more cameras around a cloud of atoms of strontium. That might collect more re-emitted light, but that would require more windows or, alternatively, mounting the cameras inside the chamber, and there’s not a whole lot of space in there for a bunch of cameras.

The option appeared, Schwartzman said, during a a brainstorming session in the lab. While they were brainstorming, scientist Joe Frisch came up with the idea for mirrors.

“What you can do is reflect the light traveling away from the cloud to the camera lens,” Cheong said. Consequently. but also more views of an object from different angles. This selection of distinct images, the team realized, meant they had devised a form of so-called “bright field imaging” and might be able to reconstruct a three-dimensional model of the cloud of atoms, not just an impression. two-dimensional.

3D printing of an idea

With the support of lab-led research and development grant, Cheong and Safdari took the idea of ​​the mirror and continued it, designing an array of tiny mirrors capable of redirecting light from all around a cloud of atoms to a camera. Using algebra and ray tracing software developed by Kagan and Vandegar.

This is the kind of thing that might seem obvious in retrospect, but it took a lot of thought to get there, Schwartzman said. “When we first came up with this we thought, ‘People must have done this before,'” he said, but in fact it’s new enough that the group has filed for a patent. on the device.

To test the idea, Cheong and Safdari made a mock-up with a 3D-printed scaffold holding the mirrors, then fabricated a micro-printed fluorescent object -3D that spells out “DOE” when viewed from different angles. in fact, collecting light from several different angles and keeping all images sharp. Additionally, their 3D reconstruction was so accurate that it revealed a small flaw in the manufacture of the “DOE” object – an arm of the “E” slightly bent downward.

The next step, according to the researchers, is to build a new variation to test the idea in a smaller atom interferometer at Stanford, which would produce the first 3D visuals of clouds of atoms. This version of the mirror dome would sit outside the chamber containing the atom cloud, so if these checks pass, the team would then build a stainless steel version of the mirror scaffold suitable for the vacuum conditions inside. inside an atom interferometer.

Schwartzman said the ideas being developed by Cheong, Safdari and the rest of the team could be useful beyond physics experiments. “It’s a new device. Our software is atom interferometry, but it can be useful in other programs,” he said, such as quality control for manufacturing small objects in industry.

The research was funded by the Department of Energy, Laboratory-Led Research and Development Program. MAGIS-100 is supported by the Gordon and Betty Moore Foundation and the DOE Business of Science.

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