We present a novel spectroscopic technique, two-color two-photon spin-noise spectroscopy, and demonstrate its application to ${}^{133}\mathrm{Cs}$ atoms. This approach encompasses both the pump-probe and nonlinear two-photon schemes, as well as an interference noise arising due to Doppler shift. In the pump-probe scheme, the pump laser populates the excited states, while the probe laser monitors spin fluctuations, enabling the study of density fluctuations in these states. The pure two-photon scheme can be used to study a spin noise in the ground state, where fluctuations in the probe beam polarization are governed by the third-order susceptibility ${\chi }^{\left(3\right)}$, offering additional advantages. We also theoretically analyze the structure of the susceptibility tensor to qualitatively interpret observed effects, such as a dependence on the pump-laser polarization plane and appearance of high harmonics of the Larmor frequency in the spin noise.

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• Fine & hyperfine structure
• Magneto-optical effect
• Noise
• Spin polarization
• Third order nonlinear optical processes
• Atoms
• Spin noise spectroscopy