Millimeter-wave spectroscopy in cesium Rydberg states. Quantum defects, fine- and hyperfine-structure measurements

High-resolution double-resonance spectroscopy experiments in the millimeter-wave domain have yielded precise values of quantum defects in the $S$, $P$, $D$, and $F$ Rydberg levels of cesium (principal quantum number $n$ ranging from 23 to 45). In addition, fine and hyperfine structures have been measured in these levels. These experiments provide a precise mapping of the cesium Rydberg levels, allowing us to predict with an accuracy of about a MHz any transition frequency between two states with $n\ge 20$ and $l\le 3$.