title: Na-Faraday rotation filtering: the optimal point.
abstract: Narrow-band optical filtering is required in many spectroscopy applications to suppress unwanted background light. One example is quantum communication where the fidelity is often limited by the performance of the optical filters. This limitation can be circumvented by utilizing the GHz-wide features of a Doppler broadened atomic gas. The anomalous dispersion of atomic vapours enables spectral filtering. These, so-called, Faraday anomalous dispersion optical filters (FADOFs) can be by far better than any commercial filter in terms of bandwidth, transition edge and peak transmission. We present a theoretical and experimental study on the transmission properties of a sodium vapour based FADOF with the aim to find the best combination of optical rotation and intrinsic loss. The relevant parameters, such as magnetic field, temperature, the related optical depth, and polarization state are discussed. The non-trivial interplay of these quantities defines the net performance of the filter. We determine analytically the optimal working conditions, such as transmission and the signal to background ratio and validate the results experimentally. We find a single global optimum for one specific optical path length of the filter. This can now be applied to spectroscopy, guide star applications, or sensing.
authors.affiliation: 1] 3. Physikalisches Institut, Universität Stuttgart, Stuttgart Research Center of Photonic Engineering (SCoPE), Pfaffenwaldring 57, D-70569 Stuttgart, Germany [2] Center for Integrated Quantum Science and Technology (IQST), Pfaffenwaldring 57, D-70569 Stuttgart, Germany.
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Kiefer
authors.affiliation: 1] Center for Integrated Quantum Science and Technology (IQST), Pfaffenwaldring 57, D-70569 Stuttgart, Germany [2] 5. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Löw
authors.affiliation: 1] 3. Physikalisches Institut, Universität Stuttgart, Stuttgart Research Center of Photonic Engineering (SCoPE), Pfaffenwaldring 57, D-70569 Stuttgart, Germany [2] Center for Integrated Quantum Science and Technology (IQST), Pfaffenwaldring 57, D-70569 Stuttgart, Germany [3] Max Planck Institute for Solid State Research, Heisenbergstraße 1, D-70569 Stuttgart, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Wrachtrup
authors.affiliation: 1] 3. Physikalisches Institut, Universität Stuttgart, Stuttgart Research Center of Photonic Engineering (SCoPE), Pfaffenwaldring 57, D-70569 Stuttgart, Germany [2] Center for Integrated Quantum Science and Technology (IQST), Pfaffenwaldring 57, D-70569 Stuttgart, Germany [3] Max Planck Institute for Solid State Research, Heisenbergstraße 1, D-70569 Stuttgart, Germany.
authors.forename: Ilja
authors.initials: I
authors.lastname: Gerhardt