Selective Diffraction Reflection in Helical Periodical Media with Large Anisotropy

Transmission and reflection of the light in films with helical periodical structure and enormous anisotropy are studied. We found strong evidence that in MgF₂ there is a range (window) of frequencies for the incident light where strong anisotropy takes place. It is shown that in helical periodical media (HPM) with large anisotropy, the circular dichroism in diffraction (selective) reflection region (DRR) decreases with the increasing of the parameter of anisotropy δ = (ϵ₁ − ϵ₂)/(ϵ₁ + ϵ₂) (where ϵ₁ and ϵ₂ are the principal values of the local dielectric constant tensor) and vanishes in the limit . The linear dichroism has the reverse behavior: it is equal to zero in the limit and increases to the maximum value equal to one in the limit . The DRR's structures were also found at certain conditions for HPM calculated in the presence of dispersion for the dielectric permittivity.

Keywords

• diffraction,
• eigen polarizations,
• large anisotropy,
• liquid crystals,
• selective reflection,
• transmission