A tunable graphene-based hyperbolic metamaterial is designed and numerically investigated in the mid-infrared frequencies. Theoretical analysis proves that by adjusting the chemical potential of graphene from 0.2 eV to 0.8 eV, the reflectance can be blue-shifted up to 2.3 µm. Furthermore, by modifying the number of graphene monolayers in the hyperbolic metamaterial stack, we are able to shift the plasmonic resonance up to 3.6 µm. Elliptic and type II hyperbolic dispersions are shown for three considered structures. Importantly, a blue/red-shift and switching of the reflectance are reported at different incident angles in TE/TM modes. The obtained results clearly show that graphene-based hyperbolic metamaterials with reversibly controlled tunability may be used in the next generation of nonlinear tunable and reversibly switchable devices operating in the mid-IR range.

The search for new low loss nematic liquid crystal mixtures with enhanced birefringence and low temperature of nematic-to-isotropic phase transition plays a pivotal role in a development of new applications in the emerging field of thermally tunable metamaterials. Here we maximize thermally induced tunability of a terahertz metamaterial by using a specially designed nematic liquid crystal mixture. It is shown that the resonant response of a metamaterial device can be effectively tuned both in terms of its magnitude and wavelength with the spectral tunability approaching the theoretical limit of 8 GHz. Electromagnetic simulations confirm our tests and match the experimental observations well. The suggested approach opens new routes for next-generation soft-matter-based filtering and sensing components and devices.

Methods of 3D imaging present on the market can be divided into two basic groups: autostereoscopic and stereoscopic. At the stereoscopic methods of 3D imaging it is necessary to use special glasses for separation of images constituting stereo-pair. The most commonly used active glasses consist of two electro-optical transducers based on twisted nematic or other electro-optical effects. Here the evaluation of liquid crystal mixtures is designed intentionally for 3D active glasses in order to eliminate drawbacks of active glasses available on the contemporary market. Material parameters of new designed liquid crystal mixtures such as: elastic constants, viscosity, refractive indices, dielectric and spectral properties as well as response times have been determined. In addition to the symmetrisation of the switching times of 3D active glasses, a dual frequency nematic liquid crystal has been proposed.[GRAPHICS].

We developed an interference method for determination refractive indices of nematic liquid crystals in a broad electromagnetic spectrum. Values of ordinary and extraordinary refractive indices were measured in VIS (from 0.4 to 0.8m), NIR (from 0.8 to 1.4m), SWIR (from 1.4 to 3.0m) and at an edge of MWIR (from 3.0 to 4.2m) regions. The main task of this work was to develop the efficient and accurate interference method. The absolute error of these measurements is not higher than 0.02. The method was tested on two newly designed mixtures. The first one was a high birefringence liquid crystal mixture for the laser rangefinder, while the second one is intentionally prepared for breathalyser application. The mixture does not possess high absorption bands at 3.4m. To measure a dispersion of the refractive indices cells with various thicknesses and dielectric mirrors were prepared. The paper presents a theoretical discussion and experimental results. [GRAPHICS] .

There exists a problem with an in situ diagnostics of contamination of ethyl alcohol in a human being exhaled air. When ethyl alcohol in a mouth blowing (in a gaseous state) exists, the characteristic CH stretch absorption bands in CH3 and CH2 functional groups in ethanol (CH3CH2OH) appear at a wavelength of λ=3.42μm. To investigate the presence of ethyl alcohol in exhaled human air, the light beam of λ=3.42μm is passing through an air sample. If one alternately measures the intensity of the investigated beam and the reference, a percentage of ethanol in the air sample can be estimated using a sensitive nondispersive infrared (NDIR) system with a stable operating flow mass detector. To eliminate a mechanical chopper and noise generating stepper motors, a photonic chopper as a liquid crystal shutter for λ=3.42μm has been designed. For this purpose, an innovative infrared nematic liquid crystal mixture was intentionally prepared. The working mixture was obtained by a selective removal of CH bonds and its exchange by heavier polar substituents, what ensures a lack of absorption band of CH bonds. The paper presents theory, concept and final experimental results of the infrared nematic liquid crystals mixture and the liquid crystal shutter for breathalyzer applications.

There exists a need in a quality and accuracy of a three-dimensional laser metrology operating in numerically controlled automatic machines. For this purpose, one sends three laser beams mutually perpendicular. These three beams of the wavelength lambda = 0.6328 mu m are generated by the same laser and are directed along three independent, orthogonal, mutually perpendicular, optical paths with a given light polarization plain. Using these beams, constituting the frame of coordinates, three independent laser rangefinders are able to determine spatial coordinates of a working tool or a workpiece. To form these optical pulses, a special refractive index matched Half-Wave Plate with nematic Liquid Crystal (LCHWP) was applied. The presented half-wave plate is based on a single Twisted Nematic (TN) cell (with the twist angle Phi = pi/2) of a rather high cell gap d similar to 15 mu m filled with a newly developed High-Birefringence Nematic Liquid Crystal Mixture (HBLCM) of optical anisotropy as high as Delta n similar to 0.40 at lambda = 0.6328 mu m, where the Mauguin limit above 5.00 similar to Delta nd >> lambda/2 = 0.32 is fulfilled.

We present an electrically tunable metamaterial device consisting of a periodic array of crossed elements embedded in nematic liquid crystal. Our experimental results show that the transmittance and absorption coefficient of the metamaterial device can be substantially tuned (with an absorption coefficient change of up to 22% for 0.82 THz) by switching the liquid crystal alignment, induced by applying an external voltages applied to the wire electrodes. Structured tunable devices may find applications in modulation and switching elements operating in the visible–infrared–terahertz and microwave regimes.

The terahertz time domain spectroscopy (THz-TDS) system is used to determine the effects of an AC bias voltage on the tunable response of a metamaterial transducer. The tunability of the metamaterial structure, which is based on the rod-split-square resonator, is demonstrated at terahertz frequencies through electrical control of the nematic liquid crystal orientation. Experimental results show that the metamaterial device can be tuned effectively (with transmittance change of up to 19%) by changing the magnitude of the AC bias voltage from 0 to 300 V. This type of tunable metamaterial could find application in the development of devices operating in the THz frequency region for filtering, modulating, and switching of the electromagnetic signals.

There exists the problem in diagnostics of dense plasma (so-called Thomson diagnostics). For this purpose the plasma is illuminated by series of high energy laser pulses. The energy of each separate pulse is as large as 3 J, so it is impossible to generate a burst of such pulses by a single laser. In this situation, the pulses are generated by several independent lasers operating sequentially, and these pulses are to be directed along the same optical path. To form an optical path with λ = 1.064 μm and absolute value of the laser pulse energy of 3 J, a special refractive index matched twisted Nematic Liquid Crystal Cell of type LCNP3, with switching on time τ ON smaller than 3 μs was applied.

High-Birefringence Nematic Liquid Crystals Mixtures (HBNLCM) recently developed in the Military University of Technology (Poland) are presented in this paper. Dielectric, refractometric, viscosimetric and elastomeric characteristic were determined. The properties are discussed in terms of their applicability to electro-optical devices. Applying HBNLCM of LCM to space mission (Phobos Ground) applications for a space-borne laser rangefinder was developed, manufactured and tested under cooperation between Military University of Technology (MUT) in Poland and Vavilov State Optical Institute (Vavilov SOI) in Russia. Transmission T of Liquid Crystal Cell (LCC) at λ=1.064 μm was not smaller than 95% at the aperture diameter not less than 15 mm. Switching on and switching off times in 2.5 μm thick LCC driven by voltage 10 V were not larger than 0.7 ms. Applying HBNLCM of LCM3 to refractive index matched twisted Nematic Liquid Crystal Cell of type LCNP4 for Thomson diagnostics of dense plasma was developed, manufactured and tested under cooperation between MUT in Poland and the National Research University of Information Technologies, Mechanics and Optics in Russia. Transmission T of LCNP4 at λ=1.064 μm was not smaller than 97% at the aperture diameter not less than 30 mm. Switching on time in 2.5 μm thick LCNP4 driven by voltage 200 V was not larger than 3 μs. LCNP4 can easily tolerate 0.42 J/cm2.

In this Letter, we report on measurements of the complex permittivity of highly anisotropic nematic liquid crystals at microwave frequencies as a function of the AC bias voltage. Permittivity measurements have been performed by the split post dielectric resonator technique. The experiments have shown that when the AC bias voltage increases from 0 to 8 V, the real part of the permittivity of these liquid crystals changes by up to 28%. The tunability and the relatively low dielectric losses observed in these liquid crystal mixtures mean that they are ideal materials for the design of tunable microwave components.

Streszczenie — Dzia³anie urz¹dzen typu ciek³okrystalicznych wyœwietlaczy graficznych opiera sie na wstepnie uporz¹dkowanej, charakteryzuj¹cej sie anizotropi¹ w³aœciwoœci optycznych (dwoj³omnoœci¹), warstwie ciek³ego kryszta³u. W niniejszym artykule omowiono technologie fotoporz¹dkowania, porownuj¹c j¹ z innymi stosowanymi dotychczas technikami uzyskiwania jednorodnej tekstury ciek³ego kryszta³u. Technologia ta jest alternatyw¹ dla najczeœciej wykorzystywanego rubbingu warstw polimerow organicznych. Zdefiniowano podstawowe wymagania stawiane warstwie porz¹dkuj¹cej ciek³y kryszta³ oraz przedstawiono wyniki badan nad ro?nymi typami przetwornikow ciek³okrystalicznych: zdjecia uzyskane przy u?yciu mikroskopu polaryzacyjnego, charakterystyki elektrooptyczne oraz czasy prze³¹czania struktury. Ocenie poddano symetryczne referencyjne komorki otrzymane z zastosowaniem warstw uporz¹dkowanych metod¹ rubbingu, komorki symetryczne z³o?one z dwoch warstw uporz¹dkowanych liniowo spolaryzowanym promieniowaniem ultrafioletowym oraz komorki asymetryczne wykonane z warstwy uporz¹dkowanej metod¹ rubbingu i warstwy fotoporz¹dkowanej za pomoc¹ ro?nych dawek promieniowania ultrafioletowego. S³owa kluczowe: fotoporz¹dkowanie, charakterystyka elektrooptyczna, wyœwietlacz ciek³okrystaliczny LCD, œwiat³o ultrafioletowe spolaryzowane liniowo LPUV, ciek³y kryszta³ LC. PHOTOALIGNMENT — NEW IMPORTANT TECHNOLOGY IN THE PRODUCTION OF ELECTRO-OPTICAL LIQUID CRYSTAL TRANSDUCERS Summary — The action of devices such as liquid crystal graphic displays is based on the previously aligned liquid crystal layer with anisotropic optical properties (birefringence). In this paper, the photoalignment technology has been described and compared with other methods used until now to achieve uniform texture of the liquid crystal. This method is an alternative to the most commonly used rubbing of organic polymer layers. The basic requirements for the layer which aligns liquid crystal were described and the results of the investigations on various types of liquid crystal transducers (microphotographs obtained using a polarizing microscope, electro-optical characteristics and characteristic structure switching times) were presented. Different types of liquid crystal cells have been evaluated: reference symmetrical cells produced with layers aligned by rubbing method, symmetrical LC cells composed of two layers oriented using linearly polarized UV beams as well as asymmetrical cells made from a layer aligned by rubbing method and a

The action of devices such as liquid crystal graphic displays is based on the previously aligned liquid crystal layer with anisotropic optical properties (birefringence). In this paper, the photoalignment technology has been described and compared with other methods used until now to achieve uniform texture of the liquid crystal. This method is an alternative to the most commonly used rubbing of organic polymer layers. The basic requirements for the layer which aligns liquid crystal were described and the results of the investigations on various types of liquid crystal transducers (microphotographs obtained using a polarizing microscope, electro-optical characteristics and characteristic structure switching times) were presented. Different types of liquid crystal cells have been evaluated: reference symmetrical cells produced with layers aligned by rubbing method, symmetrical LC cells composed of two layers oriented using linearly polarized UV beams as well as asymmetrical cells made from a layer aligned by rubbing method and a layer photoaligned using different UV radiation doses.

There exists a problem in diagnostics of a dense plasma (so-called Thomson diagnostics). For this purpose, the plasma is illuminated by series of high energy laser pulses. Such pulses are generated by several independent lasers operating sequentially, and these pulses are to be directed along an exactly the same optical path. In this case, the energy of each separate pulse is as large as 3 J, so it is impossible to generate a burst of such pulses by a single laser. In this situation, several independent lasers have to be used. To form optical path with λ = 1.064 μm and absolute value of the energy of laser pulse through of 3 J, a special refractive index matched twisted Nematic Liquid Crystal Cell (NLCC) of type LCNP2 with switching on time τON smaller than 5 μs might be applied. High laser damage resistance of NLCC and short τON can be fulfilled by preparation of liquid crystal cells with Liquid Crystal Mixture (LCM), well tuned to twisted nematic electro-optical effect, and well tuned all optical interfaces (Air – Antireflection – Quartz Plate – Electrode – Blocking Film – Aligning Layer – LCM – Aligning Layer – Blocking Film – Electrode – Quartz Plate – Antireflection – Air). In such LCNP2 cell, the transmission is higher than 97% at λ = 1.064 μm, as it is presented by Gooch and Tarry [J. Phys. D: Appl. Phys. 8, 1575 (1975)]. The safe laser density energy is about 0.6 J/cm2 for a train of laser pulses (λ = 1.064 μm, pulse duration 10 ns FWHM, pulse repetition rate 100 pps, train duration 10 s), so the area of liquid crystal cell tolerating 3 J through it shall be as large as 5 cm2. Due to the presence of two blocking film layers between electrodes, LCNP2 can be driven by high voltages. Switching on time smaller than τON = 5 μs was obtained under 200 V switching voltage.

A split post dielectric resonator is used to determine the effect of AC bias voltage on the microwave complex permittivity of nematic liquid crystals. High resistivity silicon transducers separated by 100 μm are bridged by nematic liquid crystals and their properties determined. The in-plane permittivity of liquid crystals can be effectively tuned (change of effective permittivity of up to 8%) by increasing the AC bias voltage from 0 to 6 V. Using high resistivity silicon allowed us to obtain tunable dielectric stacks with relatively small dielectric losses at microwave frequencies.

We analysed the response of a tunable liquid crystal metamaterial transducer in the terahertz frequency range. Tunability of scattering parameters is achieving by an in-plane switching (IPS) effect. The metamaterial structure is based on Ω-shape resonators. A full-wave analysis technique based on the finite-difference time-domain (FDTD) method was performed using the QuickWave 3D electromagnetic solver. Terahertz transmission properties of the metamaterial structure can be controlled by the director of the liquid crystal layer. The effective refractive index for operation frequency varies from negative to positive values. A novel approach to switching of metamaterial transducer by IPS mode is presented.

In the present work we have synthesized a novel composite materials based on praseodymium (Pr3+) doped La2CaB10O19 (LCBO: Pr3+) nanocrystallites embedded into the polymethylmethacrylate (PMMA) and polycarbonate (PC) matrices for laser operated devices. It was shown that the SHG is very sensitive to the wavelength of external light.The optimal content of the LCBO: Pr3+ nanocrystallites sized within the 30–110 nm range was equal to 5.7 wt%. It was shown that the SHG is very sensitive to the wavelength of external photoinducing illumination.

In the present work the usefulness of photoalignment as a nematic liquid crystal aligning technique has been evaluated. A photocrosslinking mechanism of photosensitive polymer material has been used to cause anisotropy in the layer. The influence of the UV dose on the LC alignment of liquid crystal material in the TN-type cell has been examined.

We analysed the response of a tunable liquid crystal metamaterial (MTM) transducer in the terahertz frequency range. The MTM structure is based on the rod double-split square resonators (SSR) with back-to-back orientation. A full-wave analysis technique based on the finite-difference time-domain method (FDTD) was performed using QuickWave 3D electromagnetic solver. Terahertz transmission properties of the MTM structure can be controlled by the director of the liquid crystal layer. The main aim of this work is to determine the impact of the size of the SSR of the MTM transducer on scattering parameters of the analysed MTM transducer at terahertz frequency range. Numerical simulations were performed in the range 0.32-0.44 THz.