Electrons emit electromagnetic radiation when they are accelerated. When an electron moves through a macroscopic magnetic field the acceleration is caused by the Lorentz force and the radiation is called synchrotron radiation. If, on the other hand, the electron is accelerated by the microscopic Coulomb (electric) field of a nucleus, the associated radiation is called bremsstrahlung. In general both types of radiation are incoherent.

We present experimental results on the influence of magnetic fields and laser polarization on electromagnetically induced transparency (EIT) using Rydberg levels of 87 Rb atoms. The measurements are performed in a room temperature vapor cell with two counter-propagating laser beams at 480 nm and 780 nm in a ladder-type energy level scheme. We measure the EIT spectrum of a range of ns 1/2 Rydberg states for n = 19 − 27, where the hyperfine structure can still be resolved. Our measurements span the range of magnetic fields from the low field linear Zeeman regime to the high field PaschenBack regimes. The observed spectra are very sensitive to small changes in magnetic fields and the polarization of the laser beams. We model our observations using optical Bloch equations that take into account the full multi-level structure of the atomic states involved and the decoupling of the electronic J and nuclear I angular momenta in the Breit-Rabi regime. The numerical model yields excellent agreement with the observations. In addition to EIT related experiments, our results are relevant for experiments involving coherent excitation to Rydberg levels in the presence of magnetic fields.

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