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An analysis is made of the propagation of electromagnetic radiation in a dielectric slab having a negative electrical conductivity, sandwiched between semiinfinite regions having the same dielectric constant but positive conductivities. The threshold conditions corresponding to zero attenuation for waves propagating in the plane of the slab are determined. For slab thicknesses that are small, compared with a wavelength, the most easily excited wave is polarized with its electric vector perpendicular to the plane of the slab but for thicker active regions the threshold is independent of polarization. These results are compared with observations of stimulated emission in p-n junction lasers.
Hall et al. (1963) studied this question.