ABSTRACT
This chapter describes a relatively non-invasive optical spectroscopy technique, known as spin noise spectroscopy (SNS), to probe spontaneous magnetization fluctuations in an alkali atomic vapor at thermal equilibrium. The atomic magnetization at a non-zero temperature fluctuates about its equilibrium value, and such magnetization (spin) noise imparts fluctuation in the measured Faraday rotation of a far-detuned, linearly polarized probe laser beam passing through the vapor. The SNS can reveal the dynamical spin properties, such as spin relaxation times, of the system with a minimal perturbation. For a system with an ensemble of electron spins at thermal equilibrium, the magnetization of the system fluctuates about its equilibrium value. The chapter presents how the spin noise spectroscopy can be used to infer the real-time spin population dynamics in different hyperfine states in neutral atoms.
