Absorption and emission of polariton modes in a ZnSe-ZnSSe heterostructure

TL;DR

This study explores how polariton modes in a ZnSe-ZnSSe heterostructure influence light absorption and emission, revealing interference effects and non-thermal polariton distributions driven by optical excitation.

Contribution

It provides a detailed experimental and theoretical analysis of polariton mode interference and non-equilibrium emission in a ZnSe-based heterostructure, highlighting the role of the polariton population distribution.

Findings

Interference peaks in reflection spectra due to polariton modes.

Emission peaks depend on pump pulse energy and are non-thermal.

Theoretical model links emission/absorption ratio to polariton population.

Abstract

We investigate the absorption and emission of a 25 nm ZnSe layer, which was grown on a GaAs buffer and cladded by ZnSSe layers. Due to the coupling of light with the exciton resonances, polariton modes propagate through the ZnSe layer. Their interferences appear as additional peaks in the reflection spectra and can be explained by the effect of spatial dispersion. We present additional experimental results for the emission of the sample after excitation by a pump pulse, showing corresponding interference peaks of the polariton modes, whose maxima strongly decrease to higher energies. Our exact theoretical analysis shows that the ratio of emission and absorption is given by the population of the globally defined states of the electromagnetic field, i.e. the polariton distribution which is generated by the pump pulse. This distribution, being far from thermal quasiequilibrium, shows pronounced peaks at the polariton modes depending on the energy of the pump pulse.