The Influence of Absorption and Gain on Photonic Density of States

TL;DR

This paper analytically investigates how absorption, gain, and structural parameters influence the photonic density of states in cholesteric liquid crystals, revealing implications for laser threshold and resonator design.

Contribution

It provides exact analytic expressions for PDS dependence on absorption, gain, and structural parameters in cholesteric liquid crystals, linking PDS to energy density and laser thresholds.

Findings

Decreasing the refractive index of surroundings sharply increases PDS.

Higher PDS correlates with lower laser excitation thresholds.

The system can function as a low-threshold laser or multi-position trigger.

Abstract

The photonic density of states (PDS) of the eigen polarizations (EPs) in cholesteric liquid crystal (CLC) cells are calculated. The exact analytic expressions for the reflection and transmission matrices for the finite thickness CLC layer are used. We obtained the dependences for the PDS on the parameters characterizing absorption and gain, as well as the CLC cell thickness, CLC local dielectric anisotropy and refractive index of CLC layer surrounding. The possibility of connections between the PDS and the density of the light energy accumulated in the medium are investigated and it was shown that these characteristics have analogous spectra and, besides, the influences of the problem parameters on these characteristics also were analogous. We have shown, that the decrement of the refractive index of CLC layer surroundings leads to a sharp increase of the maximum PDS and, consequently, leads to a sharp decrement of the laser excitation threshold. The PDS dependence on the refraction coefficients of the substrates of the Fabry-Perot resonator filled with a CLC planar layer was investigated, too. It is shown that the subject system can work as a low threshold laser or a multi-position trigger.