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Chaos iii lasers has a significant conceptual meaning, l)ecause fuiidarneiital models of lasers, which are (leriVed from well- recognized semiclassical laser equations (i. e. . Maxwell-Bloch equations ), possess inherent instal)ility leading to chaos. rF1ese models provide promising prototypes for investigating complex dynamical behaviors in strong connection with experimental demonstrations. These include Casperson instai)ility in inhomogeiieously l)roadened single-mode lasers l)ased on mode splittiiig' leading to chaos featuring period(1oul)Ii1g, breakup of a 2-torus and intermittency2 and Lorenz chaos in homogeneously broadened singlemode lasers featuring self-sustained Rabi precessions.3 However. these types of laser chaos have been restricted to the rather iionpractical far-infrared lasers (class (1 lasers). Titus, the question arises as to whether such chaotic behaviors take place in more practical laser devices, such as C02, soli(l-state, and semiconductor laser diodes (LDs). In such lasers, polarization decay tiiiie is much shorter thait other time scales involving lasing. As a result, polarization dynamics are adiabatically eliminated in Maxwe!l-Bloch (MB) laser equations. This implies that MB instability can never been expected iii ordinary situations 1)ecause of the lack of degrees of freedom. This essential difficulty can l)C removed of COIIF5C l)V intro(lucing other degrees (:)f freedoms in the form of external modulation, light injection. introduction of saturable absorber, external feedback and so on.4 Among these lasers, which are ofteii categorized as class B lasers, LDs have an important inherent characteristic which cannot be expected in other lasers. That is an anomalous dispersion effect at the lasing frequency and the free-carrier plasma effect. These effects result in carrier-density dependent refractive ill(lex, which is expressed by the so-called o-parameter. A resultant large (3) nonlinearity gives rise to a variety of nonlinear phenomena in LDs in addition to the lasing action itself. This paper reviews various phenomeiia reported so far. paying special attention to experimental demonstrations and their physical interpretations.
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