Zeeman splitting and Faraday rotation associated with Mn ^{+ 7}P_J ⁷S₃ absorption: Photon-trap spectroscopy and quantum-theory analysis

A novel experimental method is presented for detection of a trace of optical absorption of mass-selected ions stored in an ion trap. Photon-trap spectroscopy (a generalized scheme of cavity ring-down spectroscopy) is the key technique, where a storage lifetime of photons in a high-Q cavity provides a ppm-level high sensitivity. Experiment was performed on the manganese ion, Mn⁺, to record ⁷P_2,3,4 ⁷S ₃ absorption spectra at around 260 nm. Zeeman splitting and Faraday rotation of the polarization plane were observed as well in the presence of a magnetic field. The high-resolution spectra show complex structures, which are fully interpreted by the quantum theory incorporating hyperfine interaction due to the Mn nuclear spin (I = 5/2). The present technique provides a novel approach to electronic and magnetic structures of mass-selected atomic, molecular, and cluster ions.