Calculation of the refractive indexes of lead chalcogenide salts and its application for injection lasers

The refractive indexes
N
of some commonly used lead and lead-tin chalcogenide salts (PbSnSe, PbSSe, PbSnTe) have been calculated for frequencies near the fundamental absorption edge. The calculations take into account the nonparabolicity of the bands and population effects, both in thermal equilibrium and under lasing conditions. In contrast to previous predictions, the interband dispersion is shown to give a major contribution both to the change of
N
, due to lasing conditions, and to the derivative
dN/dn
(where
n
is the minority carrier concentration). Good agreement has been obtained between our calculations and experimental results for the dispersion of
N
, for
\epsilon_{\infty}
, for the effective
N
in corrugated laser structures, and for the laser linewidth enhancement factor α. These calculations may be quite useful for the design of injection lasers and infrared devices.