Figure 4 - uploaded by Ashot Gevorgyan
Content may be subject to copyright.
Source publication
We investigated the features of the optical properties of magnetoactive cholesteric liquid crystals (CLCs) in an external static magnetic field. The boundary-value problem of light transmission through a finite layer of a magnetoactive CLC at normal light incidence and light reflection from a half-space is considered. We also investigated the evolu...
Citations
... Chiral media both natural and artificial find their applications in a control of the properties of electromagnetic fields [1][2][3][4][5][6][7][8][9][10]. One of the particular cases of the chiral media is represented by a helical medium that is the medium with permittivity tensor possessing the helical symmetry. ...
... One of the particular cases of the chiral media is represented by a helical medium that is the medium with permittivity tensor possessing the helical symmetry. Among the helical media are the cholesteric liquid crystals, the C * -smectics [1,2,4,6,[8][9][10], and the metamaterials composed of dielectric [3,[11][12][13][14][15][16] or [5,7,[17][18][19][20][21][22] conducting spirals. It is known that the electromagnetic waves in such media possess a chiral forbidden band [1][2][3][4][5][6][7][8][9][10][23][24][25][26][27]. ...
... Among the helical media are the cholesteric liquid crystals, the C * -smectics [1,2,4,6,[8][9][10], and the metamaterials composed of dielectric [3,[11][12][13][14][15][16] or [5,7,[17][18][19][20][21][22] conducting spirals. It is known that the electromagnetic waves in such media possess a chiral forbidden band [1][2][3][4][5][6][7][8][9][10][23][24][25][26][27]. This property makes it possible to use these media as filters or converters of the circular polarization of the electromagnetic waves propagating along the helical axis of the medium. ...
The propagation of electromagnetic waves in helical media with spatial dispersion is investigated. The general form of the permittivity tensor with spatial dispersion obeying the helical symmetry is derived. Its particular form describing the medium made of conducting spiral wires with pitch 2π/|q| and chirality sgn(q) is studied in detail. The solution of the corresponding Maxwell equations is obtained in the paraxial limit. The dispersion law of the electromagnetic field modes, their polarization, and the integral curves of the Poynting vector are analyzed. The dispersion law of photons in such a medium possesses polarization dependent forbidden bands. The widths of these gaps and their positions are tunable in a wide range of energies. If the helix angle α is not close to π/2 and the plasma frequency ω p ≪ |q|, then there are two chiral forbidden bands. The energies of one chiral forbidden band are near the plasma frequency ω p and the width of this gap is of order |q|. The other chiral forbidden band is narrow and is located near the photon energy |q|. In the case α ≈ π/2, the first chiral forbidden band becomes a total forbidden band. If, additionally, the plasma frequency ω p ≫ |q|, then the second forbidden band turns into a wide polarization dependent forbidden band. For the energies belonging to this interval the photons with only one linear polarization are transmitted through the medium and the polarization plane of transmitted photons is rotated. In the nonparaxial regime, the solution of the Maxwell equations is obtained in the shortwave approximation. The dispersion law of the electromagnetic field modes, their polarization, and the integral curves of the Poynting vector are found. Scattering of the electromagnetic waves by a slab made of the helical wired medium is considered.
... Strong changes in reflection in the I type PBG for left and right circular polarizations in the cases g>0, p>0 and g<0, p<0 are conditioned by the following fact. If in the cases g<0, p>0 and g>0, p<0 the polarizations of eigen modes (eigen polarizations) practically coincide with orthogonal circular polarizations as in the case of absence of external magnetic field, then in the cases g>0, p>0 and g<0, p<0 the eigen polarizations (EPs) are characterized by strong dispersion, varying in considerable intervals, especially at large values of g (absolute value) [54]. At g = ±0.58 ...
We investigated the absorption properties of photonic structures with both large optical activity and magneto-optical activity parameters. The photonic structure is a periodic helical 1D medium in an external magnetic field. The magneto-optical activity parameter g change effects on the absorption nonreciprocity spectra for both linear and circular polarizations and those for unpolarized (natural) light were investigated. We showed that in certain cases, the external magnetic field leads to a strong increase in light trapping, absorption, and absorption nonreciprocity. This system can operate as a powerful light source and asymmetric and tunable wide range high absorber as well. We also investigated the dependence of Q (total energy absorbed in a finite spectral range) and its density on the layer thickness for different values of magneto-optical activity parameter g. With a change in the parameter g, the value of Q changes over a wide range (increasing or decreasing over 40 or more times), i.e., we have a broadly tunable and nonreciprocal integral absorption, again, for both polarized and unpolarized light. We showed that there are values of the parameter of magneto-optical activity at which the integral absorption does not depend on the polarization of the incident light.
... In recent years, mechanisms of magneto-optical effects enhancement in heterostructures which combine magnetism and natural chirality [11] or structural chirality [12][13][14] have been of great interest. However, these works considered the case when the magneto-optical activity parameter g is constant and independent of wavelength. ...
... The polarization-sensitive photonic band gap (PBG) lies between the wavelengths λ 1 = pn o and λ 2 = pn e , where and . In the presence of external magnetic field magneto-optical properties of helically structured PCs in the case when the magneto-optical activity parameter g is constant and independent of wavelength were presented in [12][13][14]. Bellow we consider the case when the magneto-optical activity parameter g depends on wavelength and all calculations were performed for a helically structured PC layer with the following parameters: ε 1 = 2.29, ε 2 = 2.143, the helix of the helically structured PC layer is right-handed, and its pitch is p = 420 nm, . Let us first investigate and compare the spectra of reflection, transmission, rotation, etc., in two cases, exactly, when g=const and when g=g(λ). ...
In this paper we investigated the magneto-optical properties of helically structured photonic crystals taking into account the wavelength dependence of magneto-optical activity parameter and wavelength independence of Verdet constant. We compare the obtained results with the case of the wavelength independence of magneto-optical activity parameter. We investigated the peculiarities of spectra of rotation, ellipticity, reflection, photonic density of states, transmission nonreciprocity in these two cases. We showed that in general these results can essentially differ from one to another and wavelength dependence of magneto-optical parameter cannot be neglected.
... After each 180/α-th layer the alignment of molecules will be repeated. The distance on which the director of CLC rotates at 360° angle is termed the pitch of CLC (p= (360/α)*a, where a-is the distance between adjacent monomolecular layers and also describes the periodicity of CLC 22 . As their twisted helical structure CLC-s are able to rotate the plane of polarization of the light, by means of optical activity; the angle of the plane of polarization rotation is given by φ=ρ*d, where ρ is the specific rotation, d is the thickness of the CLC layer (cell). ...
... For instance, for quartz it is about 15.5°/mm whereas for CLC-s it is about 60000-70000°/mm. Such a great specific rotation of the plane of polarization for CLC-s and their high sensibility to external fields makes possible to control the state of polarization of light propagating through 22 . ...
In this work we have experimentally investigated optical properties of multilayered structure, consisting of two right handed Cholesteric Liquid Crystal layers with the same pitch and Rhodamine 6G (R6G) doped polymethyl metacrylate (PMMA) thin film sandwiched between them. Particularly transmission spectrum dependence on temperature is studied. The 10 nm of CLC selective reflection band tuning is achieved. The photoluminescence of R6G is registered.
The development of novel additives ensuring improved performance of lubricating materials is one of the pressing problems
of modern tribological engineering. In this respect. liquid crystals (LC) have captured keen attention of tribologists due
to their unique lubricity, the experience accumulated in this sphere has proved that LC behave most efficiently as antifrictional
additives when found in the mesomorphic state.
The work presents investigation results of the mesomorphic state and lubricating action of cholestric LC distinguished by
their chemical structure and physical properties, and their mixtures with Vaseline oil. The phase slate and the phase transition
temperature of LC structures were estimated by the polarizing microscopy with application of a purposefully manufactured device.
The device is intended to visualize and perform a continuous control of phase variations in LC mixtures in response to temperature.
The tribological tests were carried out within the temperature interval 0.1÷0.5 m/s and 0.1÷3.0 MPa loads for the steel-on-steel
friction pair using a face friction machine following the disc-on-cylinder end geometry under a given test temperature.
The procedure and results of investigations of mesomorphic-state composite lubricants by optical and viscosimetric methods are presented.
