Polarization oscillations of coupled laser beams in an optically pumped atomic vapour

Abstract

Spontaneous polarization oscillations are observed to develop in two laser beams interacting in an atomic vapour when their polarizations are locked to each other. In a theoretical analysis of the situation, we show that these oscillations are due to ground- state magnetization undergoing Larmor precession. The gain of the feedback loop that locks the two polarizations acts as a control parameter that can cause a phase-transition of the combined system (atoms and laser beams) into a stable limit cycle.