Advancing Basic Science

Getting in Tune with Atoms

Barely Above Absolute Zero

Keeping Time with Atoms

NIST's Atomic Clock - a Look Inside

Viewing Invisible Worlds

More Researcher info on the NIST web site

Lasers slow the movement of the cesium atoms, cooling them to near absolute zero.

The atoms form a ball-shaped cloud at the intersection of the laser beams.

The ball is tossed upward. It passes through a cavity filled with microwaves, stops at the top of the chamber, and falls back down through the microwaves again.

Most of the atoms absorb microwave energy and change to a higher energy state. (Atoms change from purple to red.)

Cesium atoms that absorbed energy in the microwave cavity emit light when hit with a probe laser beam. (See the yellow atoms.)

The entire process is repeated and the microwave energy changed slightly until the cesium atoms give off the greatest amount of light.

The microwave energy that produces the strongest light signal is the natural resonance frequency of cesium and is used to define the second.