Linear and circular dichroisms of cholesteric liquid crystals in a longitudinal external magnetic field

ABSTRACT

We investigated the properties of linear and circular dichroisms of cholesteric liquid crystal layer in external static magnetic field directed along helix axis. We showed that when the direction of light propagation and the direction of external magnetic field coincide, increasing the latter magnitude leads to a decrease in the linear dichroism, whereas when these directions are opposite, increasing the external magnetic field ($B_{ext}$) magnitude leads an increase in the linear dichroism. The presence of external magnetic field leads to the shift of circular dichroism curves both along wavelength axis and along dichroism axis. Then, we investigated the peculiarities of dichroism dependencies on $B_{ext}$ for different wavelengths of incident light. We compared the dependence of circular dichroism on $B_{ext}$ for a magnetically active cholesteric liquid crystal layer and an isotropic magnetically active layer and showed that while these dependencies are similar for wavelengths away from the photonic band gap, diffraction significantly affects these dependencies for wavelengths near and inside the photonic band gap. We investigated the evolution of spectra of linear and circular dichroisms at the change in $B_{ext}$, too. The results obtained can find application in the design of innovative polarised optoelectronic devices.

GRAPHICAL ABSTRACT

KEYWORDS:

• Magnetoactive cholesteric liquid crystals
• circular and linear dichroisms
• photonic band gap
• tunable polarisation narrow band or broad band filters and mirrors

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

AHG, NAV and IME acknowledge the financial support from the Foundation for the Advancement of Theoretical Physics and Mathematics ‘BASIS’ [Grant No. 21-1-1-6-1], and KBO acknowledge the EU NextGenerationEU through the Recovery and Resilience plan for Slovakia under the project no. 09103-03-V01-00052.