  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.
