  The correlation spectroscopy has been successfully employed in the
measurement of the intrinsic linewidth of electromagnetically induced
transparency (EIT) in time and frequency domain. We study the role of the
sidebands of the intense fields in the measured spectra, analyzing the
information that can be recovered working with different analysis frequencies.
In this case, the non-zero one-photon detuning appears as a necessary condition
for spectrally resolving the sideband resonances in the correlation
coefficient. Our experimental findings are supported by the perturbative model
defined in the frequency domain.
