How to measure the Mueller matrix of liquid-crystal cells
TL;DR: In this paper, a Mueller-matrix spectrometer was constructed to perform fast, dynamic measurements of the Mueller matrix of small areas of liquid-crystal cells throughout the visible range, which can be used for comparison with theoretical calculations, the determination of material parameters and modelling of the cell as an optical building block for technological use.
Abstract: The Mueller matrix is the transfer matrix in the Stokes algebra that describes the polarization of natural light. This matrix is very versatile for the task of characterizing the optical properties of liquid-crystal cells, since it can be used for comparison with theoretical calculations, the determination of material parameters and the modelling of the cell as an optical building block for technological use. We have constructed a Mueller-matrix spectrometer, with the ability to perform fast, dynamic measurements of the Mueller matrix of small areas of liquid-crystal cells throughout the visible range. To illustrate the potential of the instrument, dynamic measurements on a ferroelectric-liquid-crystal cell are presented and analysed. The optical measurements indicate that there is an asymmetry between the up and the down state, tilted smectic layers and polarization reversal initiated at the boundaries.
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TL;DR: In this paper, a method for a continuous control of the pretilt angle of the easy axis in the range 0-90° degrees and of the anchoring strength by using nanostructured polymers as alignment layers is described.
Abstract: A method for a continuous control of the pretilt angle of the easy axis in the range 0-90° degrees and of the anchoring strength by using nanostructured polymers as alignment layers is described. The nanostructured polymers are blends of two different side-chain polymers each of them promoting planar and homeotropic alignment, respectively. A model to interpret the alignment of a nematic liquid crystal induced by such polymer layers is proposed. We show that in this case the anisotropic part of the surface tension can be approximated by a simple extension of the Rapini-Papoular expression. The predicted trend of the pretilt of the easy axis versus the concentration of the side-chain polymer promoting the planar alignment, for instance, is in good agreement with the experimental data. We also show that the effective anchoring strength of the system depends on the concentration of the side-chain polymer promoting planar alignment, and exhibits a minimum for a well-defined value of this quantity. The results obtained in this work seems to be of importance for liquid crystal displays technology since the control of the pretilt and the anchoring strength strongly affect the performance of liquid crystal displays.
11 citations
TL;DR: In this paper, two novel alignment concepts have been introduced: electrically commanded surfaces (ECS) and high-performance alignment layers (HiPAL) for liquid-crystal displays.
Abstract: — The solid-surface/liquid-crystal interactions, defining the field-free alignment of the liquid crystal in conventional liquid-crystal displays, are playing a vital role in their optical appearance and performance. Nano-scale changes in the solid-surface structure induced by light have been recently shown to affect the anchoring strength and the easy-axis direction. Fine tuning of the anchoring strength is also demonstrated by nano-structuring of the Langmuir-Blodgett monolayer employed as liquid-crystal alignment layers promoting homeotropic orientation. On the basis of nano-engineering of the surface alignment properties, two novel alignment concepts have been introduced: electrically commanded surfaces (ECS) and high-performance alignment layers (HiPAL). Nano-structured polymers related to these concepts have been designed, synthesized, and used as materials for alignment layers in LCDs. ECS materials belong to the category of active alignment materials designed to mediate switching of the liquid crystal, whereas the HiPAL materials make possible the control of the molecular tilt angle in a broad range, from 0° to 90°, and they seem to enable the control of the anchoring strength as well. The nano-structured alignment materials are strong candidates for implementation in a new generation of advanced liquid-crystal displays and devices.
9 citations
TL;DR: In this article, a continuous or discontinuous transition from vertical to planar alignment was found in nematic cells, containing polyimide alignment layer exposed to linear polarized UV light, depending on whether the alignment layer was mechanically rubbed or not prior the illumination.
Abstract: Continuous or discontinuous transition from vertical to planar alignment was found in nematic cells, containing polyimide alignment layer exposed to linear polarized UV light, depending on whether the alignment layer was mechanically rubbed or not prior the illumination. The polyimide material is designed originally to promote vertical alignment when deposited onto the inner cell substrates' surface. The mechanism behind these observations is complicated. It includes inclination of the alkyl side chains of the polyimide alignment layer towards the rubbing direction and the bond breaking process due to UV illumination which are considered as the key factors for occurrence of such alignment transition.
7 citations
TL;DR: This laser photothermal mechanism allows the directional and continuous alignment of supramolecular structures over an arbitrary large area with the easy control of laser irradiation and enables area-selective orientation of the supramolescular structures for device-oriented nanopatterning.
Abstract: Controlling the orientation of highly periodic supramolecular structures of small feature size (<5 nm) is the first step for potential applications in optoelectronics, membranes, and template synthesis. A new method, namely, laser photothermal writing, is introduced to direct the orientation of supramolecular columns over a large area. Supramolecular columns consisting of taper-shaped molecules with long aliphatic tail groups are aligned by a thermal gradient, which is induced by exposing a near-infrared laser beam to a graphene photothermal conversion layer. Intriguingly, the orientation of the supramolecular columns can be controlled in a facile manner by varying the laser scanning velocity and power. In contrast to previous methodologies for aligning supramolecular structures, this laser photothermal mechanism allows the directional and continuous alignment of supramolecular structures over an arbitrary large area with the easy control of laser irradiation. Besides, the laser process also enables area-selective orientation of the supramolecular structures for device-oriented nanopatterning.
7 citations
TL;DR: In this paper, the orientation of liquid crystal molecules on an alignment film was studied using Fourier transform infrared spectrometer (FTIR) with polarisation mode, and the standard laboratory instrument was used to simultaneously determine the alignment direction and pretilt angle.
Abstract: The orientation of liquid crystal molecules on an alignment film was studied using Fourier transform infrared spectrometer (FTIR) with polarisation mode. The standard laboratory instrument was used to simultaneously determine the alignment direction and pretilt angle of the liquid crystal molecules. The dipole of the infrared active moiety of the rigid biphenyl of liquid crystal molecules can be used to represent their orientation, and the polarised light electrical vector coinciding with the dipole of the infrared active moiety increases in absorption intensity. Thereby, the infrared light absorbance of liquid crystal molecules in liquid crystal cells as a function of the polarised angle of incident light reveals the orientation of molecules, and the size of pretilt angle can be calculated. In particular, this method has no restriction on the range of pretilt angle.
7 citations
References
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TL;DR: In this paper, a general symmetry argument is presented, and experiments on newly synthesized p-decyloxybenzylidene p'-amino 2-methyl butyl cinnamate are described, demonstrating that chiral smectic C and H liquid crystals are ferroelectric.
Abstract: A general symmetry argument is presented, and experiments on newly synthesized p-decyloxybenzylidene p'-amino 2-methyl butyl cinnamate are described, demonstrating that chiral smectic C and H liquid crystals are ferroelectric. Some of the properties of this new class of ferro-electrics are discussed.
1,357 citations
TL;DR: In this article, the general theory developed in Part I and the derivation of the matrices representing two optical elements which were not treated in Parts II and III are discussed. But the discussion is limited to monoclinic and triclinic crystals which do not possess optical activity.
Abstract: Part IV is divided into two sections. The first is devoted to some additions to the general theory developed in Part I, and the second section to the derivation of the matrices representing two optical elements which were not treated in Parts II and III: (1) plates possessing circular dichroism, and (2) plates cut from crystals of such low symmetry that the principal axes of absorption and refraction are not parallel. In case (2), the discussion is limited to monoclinic and triclinic crystals which do not possess optical activity.
1,316 citations
"How to measure the Mueller matrix o..." refers methods in this paper
...The Jones algebra is adequate for coherent and monochromatic light, whereas the Stokes algebra is better for natural light, which mostly is incoherent, polychromatic and unpolarized....
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...We then have the choice between the Jones [1] and the Stokes [2] algebra for the description of the polarization....
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TL;DR: In this paper, the authors decompose a Mueller matrix into a sequence of three matrix factors: a diattenuator, followed by a retarder, then followed by depolarizer.
Abstract: We present an algorithm that decomposes a Mueller matrix into a sequence of three matrix factors: a diattenuator, followed by a retarder, then followed by a depolarizer. Those factors are unique except for singular Mueller matrices. Based on this decomposition, the diattenuation and the retardance of a Mueller matrix can be defined and computed. Thus this algorithm is useful for performing data reduction upon experimentally determined Mueller matrices.
1,220 citations
"How to measure the Mueller matrix o..." refers background or methods in this paper
...The general partial polarizer P , a diattenuator, is given by the following 4 × 4 matrix (see [6]):...
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...A good reference article about polarimetry and the Mueller matrix has been written by Chipman [5]....
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...This factorization has been shown earlier by Lu and Chipman [6]....
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01 Jul 2009
TL;DR: In this paper, a stream of polarized light is decomposed into two streams which, after having been modified in a slightly different manner, are reunited, the mixture is found to have acquired properties which are quite distinct from those of the original stream, and give rise to a number of curious and apparently complicated phenomena.
Abstract: W hen a stream of polarized light is decomposed into two streams which, after having been modified in a slightly different manner, are reunited, the mixture is found to have acquired properties which are quite distinct from those of the original stream, and give rise to a number of curious and apparently complicated phenomena. These phenomena have now, however, through the labours of Young and Fresnel, been completely reduced to law, and embraced in a theory, the wonderful simplicity of which is such as to bear with it the stamp of truth. But when two polarized streams from different sources mix together, the mixture possesses properties intermediate between those of the original streams, and none of the curious phenomena depending upon the interference of polarized light are manifested. The properties of such mixtures form but an uninviting subject of investigation; and accordingly, though to a certain extent they are obvious, and must have forced themselves upon the attention of all who have paid any special attention to the physical theory of light, they do not seem hitherto to have been studied in detail. Were the only object of such a study to enable us to calculate with greater facility the results obtained by means of certain complicated combinations, the subject might deservedly be deemed of small importance.
452 citations
TL;DR: Mise en evidence de the structure par des etudes de diffusion de rayons X haute resolution d'echantillons minces smectiques C prepares entre deux lames solides par refroidissement a partir de the phase smectique A.
Abstract: Mise en evidence de la structure par des etudes de diffusion de rayons X haute resolution d'echantillons minces smectiques C prepares entre deux lames solides par refroidissement a partir de la phase smectique A
446 citations
"How to measure the Mueller matrix o..." refers background in this paper
...This tilt determination usually requires x-ray measurements [3]....
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