Parametrising Harmonic Strengths in Raman Driven Spin Noise Spectra of Neutral Atoms

We study the appearance of harmonics in spin noise correlations as a result of strong optical drive using a pair of coherent Raman beams in hot Rubidium vapour. In addition to the fundamental spin noise mode, we detect multiple equi-spaced coherence signals, including first, second, third, and fourth harmonics with relative amplitudes ranging from 10-1 to 10-4. We parametrise these higher harmonics with Raman and probe beam intensity, density of atoms, magnetic field strength and drive frequency. These observations allow us to precisely estimate the energy spacing between magnetic sub-levels in a multi-level atomic system under the influence of external magnetic fields. Our findings highlight this method as a versatile tool for optical probing and precision metrology of complex spin dynamics.