Faraday-rotation fluctuation spectroscopy with static and oscillating magnetic fields

By Faraday-rotation fluctuation spectroscopy, one measures the spin noise via Faraday-induced fluctuations of the polarization plane of a laser transmitting the sample. In the first part of this paper, we present a theoretical model of recent experiments on alkali-metal gas vapors and semiconductors, done in the presence of a static magnetic field. In a static field, the spin noise shows a resonance line, revealing the Larmor frequency and the spin-coherence time T₂ of the electrons. Second, we discuss the possibility to use an oscillating magnetic field in the Faraday setup. With an oscillating field applied, one can observe multiphoton absorption processes in the spin noise. Furthermore, an oscillating field could also help to avoid line broadening due to structural or chemical inhomogeneities in the sample, and thereby increase the precision of the spin-coherence time measurement.