Coupled ion pairs in solids under the influence of a coherent radiation field

The coupled ion pairs were modeled by two coupled two-level systems. The resulting Bloch equations were derived by the density-matrix formalism. They were solved numerically for identical ions and for slightly detuned ions with identical wave functions as a first approximation to the problem of inhomogeneous line broadening in solids. The following results mere found: (1) intrinsic optical bistability as a function of the applied laser field; (2) regions of stability, instability, and multistability for different detunings and couplings of the ions at different laser fields; (3) asymmetric shapes of the absorption lines with unstable regions; and (4) suppression of the photon echo due to the nonlinear chaotic dynamics of the coupled ions. Experimental evidence is given which supports the computer calculations.