We investigate atom-based electric-field calibration and polarizationmeasurement of a 100-MHz linearly polarized radio-frequency (RF) field usingcesium Rydberg-atom electromagnetically induced transparency (EIT) in aroom-temperature vapor cell. The calibration method is based on matchingexperimental data with the results of a theoretical Floquet model. The utilized60$D_J$ fine structure Floquet levels exhibit $J$- and $m_j$-dependent AC Starkshifts and splittings, and develop even-order RF-modulation sidebands. TheFloquet map of cesium 60$D_J$ fine structure states exhibits a series of exactcrossings between states of different $m_j$, which are not RF-coupled. Theseexact level crossings are employed to perform a rapid and precise ($\pm 0.5\%$)calibration of the RF electric field. We also map out three series of narrowavoided crossings between fine structure Floquet levels of equal $m_j$ anddifferent $J$, which are weakly coupled by the RF field via a Raman process.The coupling leads to narrow avoided crossings that can also be applied asspectroscopic markers for RF field calibration. We further find that theline-strength ratio of intersecting Floquet levels with different $m_j$provides a fast and robust measurement of the RF field's polarization.
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