Rubidium atomic clocks are compact, inexpensive and widely used, often as auxiliary frequency standards. Known for their excellent short-term frequency stability, they are key components in systems such as satellite navigation and telecommunications. Rubidium atomic clocks work by using the ultrafine transitions of rubidium atoms at a frequency of 6.8 GHz to stabilize a crystal oscillator.

How they work:

1. Rubidium Vapor: Rb clocks utilize a rubidium vapor cell where the atoms are excited by light from a rubidium discharge lamp.  

2. Microwave Resonance: Microwave energy is applied to the cell, and the atoms transition to an intermediate energy level if the frequency matches the hyperfine transition.  

3. Light Absorption: When the atoms are in the intermediate state, they absorb more light, which is detected by a photodiode.  

4. Stabilization: The output of the photodiode is used to control a microwave source, ensuring that the frequency is maintained at the precise rubidium transition frequency.      

Key Features:

Compact and Inexpensive: Compared to other atomic clock types like cesium, Rb clocks are more affordable and smaller in size.    

Short-Term Stability: They offer excellent short-term frequency stability, making them suitable for applications requiring accurate timekeeping.    

Versatile Applications: Rb clocks are used in various systems, including satellite navigation (like GPS and Galileo), telecommunications, and test equipment.    

Examples of Use:

Satellite Navigation: Rb clocks are used in GPS and other satellite navigation systems to provide precise timekeeping for position calculations.  

Telecommunications: They are used to synchronize frequencies in cellular networks and other communication systems.  

Test Equipment: Rb clocks are used as frequency standards in various test and measurement equipment.      

In summary, Rb atomic clocks are a reliable and versatile technology that plays a vital role in modern systems requiring precise timekeeping.