How Does the NIST-7 Atomic Clock Work?

The NIST-7 can be broken down into:

  • Source of Cesium Atoms – in many energy states.
  • Laser A – Puts atoms into the lowest energy state.
  • Microwave Cavity – Microwaves at just the right frequency cause atoms to change to a higher, excited energy state.
  • Frequency Divider – Converts the very high microwave frequency (about 9 billion cycles per second) to lower frequencies that are easier to use for counting.
  • Servomechanism – Changes the frequency of the microwaves in the cavity to put the greatest number of atoms into the excited state, which results in the largest light signal on the detector.
  • Laser B – Causes atoms in the excited state to emit light.
  • Detector – Detects the emitted light.
Caption:
The NIST-7 provided a standard frequency rather than the time of day. To define the length of a second, the instrument measured with exquisite precision the frequency of microwaves absorbed by Cesium 133 atoms.
Type: Illustration
Image Date: 2012
Credit: National Air and Space Museum, Smithsonian Institution.
Origin: National Air and Space Museum, Smithsonian Institution.
Creator: Bruce Morser
Innovations
Navigation Methods
 
The NIST-7 provided a standard frequency rather than the time of day. To define the length of a second, the instrument measured with exquisite precision the frequency of microwaves absorbed by Cesium 133 atoms.