  High degrees of intensity correlation between two independent lasers were
observed after propagation through a rubidium vapor cell in which they generate
Electromagnetically Induced Transparency (EIT). As the optical field
intensities are increased, the correlation changes sign (becoming
anti-correlation). The experiment was performed in a room temperature rubidium
cell, using two diode lasers tuned to the $^{85}$Rb $D_2$ line ($\lambda =
780$nm). The cross-correlation spectral function for the pump and probe fields
is numerically obtained by modeling the temporal dynamics of both field phases
as diffusing processes. We explored the dependence of the atomic response on
the atom-field Rabi frequencies, optical detuning and Doppler width. The
results show that resonant phase-noise to amplitude-noise conversion is at the
origin of the observed signal and the change in sign for the correlation
coefficient can be explained as a consequence of the competition between EIT
and Raman resonance processes.
