  We observe electromagnetically induced transparency (EIT) in Rb vapor at
various optical intensities, starting from below saturation to several times
the saturation intensity. The observed Lorentzian width of the EIT signal is
very small. Solving the time dependant density matrix equation of motion with a
phenomenological decay constant, we find an expression suitable in explaining
the EIT signal. In this experimental observation and theoretical analysis
intensity of EIT signal and its Lorentzian width increases with Rabi frequency
of optical field.
