Non‐Linear Dipole Effects in the Infra‐Red Absorption of GaAs

The IR absorption spectrum of GaAs is calculated and a good agreement with the measured bands is achieved. A considerable part of the two phonon bands is due to second order dipole moment absorption. The simplest kind of a model for cubic anharmonicity and the second order dipole moment has proved to work satisfactorily. The constant ratio between dipole and anharmonic coupling coefficients characteristic for this type of interaction is represented in terms of optical constants and the static ionic charge. The difference between an effective value for this ratio taken from the IR data and the one valid for the short range type of coupling coefficients is of reasonable magnitude.