Microwave field strength measurement in a rubidium clock cavity via adiabatic rapid passage

Rubidium atomic frequency standards have been found to display a strong frequency dependence on the microwave power density or field intensity. It is, therefore, desirable to have simple and easily applied techniques for measuring not only the field strength but also the field distribution within the clock’s microwave cavity. A technique which makes use of adiabatic rapid passage (ARP) to measure field strengths in Rb clock cavities is described and demonstrated. Measurements using this technique are found to agree with field strengths extracted using standard microwave procedures. The ARP technique is particularly valuable in cavities where standard microwave measurements cannot be made.