From National Geographic:

Scientists have taken the first ever snapshot of an atom’s shadow—the smallest ever photographed using visible light. The imaging technique could have big implications for genetic research and cryptography, researchers say.

The pioneering shutterbugs used an electrical field to suspend a charged atom, or ion, of the element ytterbium in a vacuum chamber. They then shot a laser beam—about a thousand times wider than the atom—at the ytterbium.

The ytterbium atom absorbed a tiny portion of the light, and the resulting shadow was magnified by a lens attached to a microscope, then recorded via a digital camera sensor.

The team used ytterbium because they knew they could create lasers of the right color to be strongly absorbed by the element.