Phase control of amplitude-fluctuation-induced bistability

We present phase control of the fluctuation-induced bistability in the thre e-level A-type system where a weak, amplitude-fluctuating component and a s trong coherent component are used as a control field. With the addition of the stochastic component, optical bistability can be produced even if detun ings of the probe and control fields from corresponding atomic transition f requencies are equal; without the addition, the medium is transparent to th e input light. Depending on the relative phase between the stochastic and c oherent parts, bistability appears or disappears and the threshold intensit y is raised or lowered.