Résumé
Spin noise spectroscopy is a quite attractive experimental tool for studying unperturbed spin dynamics and magnetic resonance in semiconductor nanostructures. However in some cases its practical interest maybe severely limited by the weakness of the spin noise signal to be detected. In this paper we examine by how much the detection of spin noise of magnetic atoms or of nuclei, in quantum wells or quantum dots, can be improved by making use of cavity-enhanced Faraday rotation. The conditions for optimized cavities are first determined. In reflection geometry it corresponds to tune the cavity to the critical point of impedance matching. It is shown that even for optimized cavities the enhancement in spin noise detection is intrinsically limited by absorption. It turns out that the cavity effect improves the spin noise detection only when the inhomogeneous broadening of the involved optical resonance is large compared to its radiative broadening.