CHAPTER 3 - INTRINSIC OPTICAL BISTABILITY EXPERIMENTS

Abstract

This chapter provides an overview of intrinsic optical bistability. Early attempts to see optical bistability were perceived as searches for absorptive bistability. The first observation of passive optical bistability was made in a Fabry–Perot resonator containing sodium (Na) vapour. The principal results of the Na experiment were: (1) first observation of optical bistability, both absorptive and dispersive; (2) discovery and understanding of dispersive bistability; (3) demonstration that neither an inhomogeneous broadening nor a nonuniform transverse spatial profile prevents bistability in general; and (4) demonstration of other optical logic functions such as transistor, clipping, and limiting action. The chapter describes an experiment in which a system was designed to provide a foreign gas to homogeneously broaden the Na. The gas served the additional function of preventing Na from reaching the Fabry–Perot mirrors. Because of the interaction of Na with most glasses at high temperatures and the insertion loss of any window, a windowless system seemed preferable. As it turned out, argon gas was not used because the laser power was insufficient to saturate the total homogeneously broadened line and because dispersive bistability was seen without it. The long narrow water-cooled tubes and bellows connecting the hot Na chamber to the Fabry–Perot end mirrors reduced the solid angle for Na atoms to strike the end mirrors. An acousto-optic modulator was used to modulate the input intensity in a triangular wave for bistability hysteresis studies. The basic idea of thermal optical bistability is to achieve purely dispersive bistability where the intensity dependence of the refractive index originates from heating. Optically-induced thermal shifts of absorption peaks or band edges can also lead to a different class of optical bistability for which external feedback is unnecessary.