  We report the discovery, theoretically, of new effects, namely, the effects
of magnetically induced transparency/absorption. The effects are observed in a
magnetically active helically structured periodical medium. Changing the
external magnetic field and absorption, one can tune the frequency and the
linewidth of the transparency/absorption band. We have shown that both effects
can be simultaneously observed for two eigenmodes of a cholesteric liquid
crystal (CLC) layer. Both effects are nonreciprocal and tunable. They can be
observed in the case of the absence of dispersion of the dielectric and the
magnetic tensor components, as well as in the case of dispersion dependences of
optical parameters of the CLC layer. Comparison of these effects show that
while the effect of magnetically induced transparency is observed at wide
intervals of variation of the parameters of the CLC layer, the effect of
magnetically induced absorption can observe only in very small intervals of
these parameters.

Optics