Physical Review A
Floquet-state perturbation theory for the radio-frequency modulation of the Mössbauer resonance
Ilkka Juhani Tittonen, Mikk Lippmaa, Juha Javanainen
Abstract
We study theoretically resonance absorption of \ensuremath{\gamma} rays by nuclei exposed to an external radio-frequency (rf) magnetic field. The external field is taken to couple directly to the nuclear magnetic moments. Perturbation theory is developed for M\"ossbauer spectroscopy in terms of Floquet eigenstates that incorporate the rf field exactly. The present treatment allows for calculation of the conventional time-averaged absorption spectrum, as well as analysis of the time dependence of absorption, resolved on the scale of a period of the rf field. An efficient numerical implementation of the theory is described and comparisons with the equally general approach of Salkola and Stenholm [M. Salkola and S. Stenholm, Phys. Rev. A 41, 3838 (1990)] are made. We demonstrate that even at off-resonance frequencies a strong modulation leads to shifts of the original static hyperfine lines. Examples of line splittings of NMR's associated with Rabi flopping are also shown. \textcopyright{} 1996 The American Physical Society.