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Angular-Dependent Spontaneous Emission in Cholesteric Liquid Crystal Films
摘要： Due to the presence of a selective reflection band, cholesteric liquid crystals (CLCs) strongly modify the emission of fluorescent guest molecules. While emission along the helical axis is well understood, the emission properties at oblique angles with respect to the cholesteric helix have so far have not been explored in detail. We present a systematic study of the angular-dependent spontaneous emission properties of dye-doped cholesteric films, including a full Stokes analysis of the emitted light. Variation of the cholesteric pitch allows us to probe the effect of the photonic band structure on spontaneous emission in a wide angular range. We find exceptional angular-dependent intensity and polarization variations of the emitted light, and give experimental proof for the splitting of the first-order reflection band as well as its overlap with the second-order band at large detection angles.
关键词： and Hybrid Materials,Optical,Cholesteric Liquid Crystal,Stokes Analysis,Angular-Dependent,Plasmonics,Spontaneous Emission,Magnetic
更新于2025-09-23 15:23:52
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[IEEE 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Xiamen, China (2019.12.17-2019.12.20)] 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Visual Measurement of Terahertz Power Based on Graphene and Cholesteric Liquid Crystal Microcapsule
摘要： We demonstrate a new method to detect terahertz (THz) power by combining cholesteric liquid crystal microcapsule (CLCM) with three-dimensional porous grapheme (3DPG). The power of the THz radiation is measured using the hue image which is digitalized from the color change of a CLCM. Based on the the rmochromic property of CLCM and the high absorption of 3DPG over 97% in the frequency range of 0.32 THz a quantitative visualization of the THz intensity up to 2.7×103 mW/cm2 is presented and the minimal detectable THz power is only 0.009 mW. The THz power meter is cost-e?ective, portable, and high e?cient, which can be used in many applications such as THz imaging, inspection and sensing.
关键词： visualization,graphene,cholesteric liquid crystal microcapsule,terahertz power
更新于2025-09-23 15:21:01
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Electrically Tunable Liquid-Crystala??Polymer Composite Laser with Symmetric Sandwich Structure
摘要： This study investigates and develops for the first time an electrically tunable liquid-crystal?polymer composite laser with a symmetric sandwich structure. This structure includes two identical polymer-stablized cholesteric liquid-crystal (PSCLC) layers, and a dye-doped nematic LC (DDNLC) layer is sandwiched between them. The PSCLC and DDNLC layers act as distributed Bragg reflectors and half-wave plate with a gain medium, respectively. The entire cell behaves as an optical cavity, where the resonant modes occur at the maxima of the cell’s transmission spectrum. Through the competition among the resonant modes by considering the gain and loss, the resonant mode with the lowest lasing threshold can be sieved out for lasing occurrence. When the same voltage is applied to the two PSCLC layers, the pitch gradients are simultaneously formed through the two layers because of the electrically induced ion-concentration gradients. When the voltage increases, the pitch gradients increase, thereby leading to the expansion of the cell photonic band gap (PBG) and blue shift of the lasing wavelength. The sandwich cell PBG can expand from 55 nm to over 170 nm, and the tuning range of the lasing wavelength is as high as 70 nm, which is the widest ever achieved in LC-related sandwich systems. The proposed configuration of the sandwich sample presents new insights into tunable LC PBG and laser devices, thereby providing potential applications in the form of sensors, medical imaging, displays and lighting, among others.
关键词： distributed Bragg reflectors,electrically tunable,dye-doped nematic LC,photonic band gap,liquid-crystal?polymer composite laser,optical cavity,symmetric sandwich structure,half-wave plate,lasing wavelength,polymer-stablized cholesteric liquid-crystal
更新于2025-09-19 17:13:59
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High-quality tuning of cholesteric liquid crystal lasers based on polymer composite system
摘要： Electrically fine tuning is demonstrated in a cholesteric liquid crystal (ChLC) laser based on the polymer composite system. Photo-polymerization in the mixture of LC monomer and LC hardly causes phase separation due to miscibility, forming a microscopically well-mixed polymer-LC composite structure like gel. Light scattering in the polymer-LC composite system decreases with increasing the polymer component, and the composite of equal parts of the polymer and LC exhibits high transparency in electric modulation of the selective reflection band, resulting in high-quality tuning of lasing wavelength in ChLC laser. In tuning operation, the ChLC laser retains a high slope efficiency greater than 19%, a low threshold smaller than 3 nJ/pulse, and a spectral linewidth narrower than 0.13 nm, while the change in lasing wavelength is fully continuous and reaches 13 nm.
关键词： selective reflection band,laser,polymer composite,cholesteric liquid crystal,electrically fine tuning
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Hyperspectral Imaging of Bio-Inspired Tilted Cholesteric Liquid Crystal Structures
摘要： The cholesteric liquid crystal (CLC) phase exhibits a helical structure with a twist axis perpendicular to the local molecular director. When light propagates in the Bragg regime through a CLC slab with a planar texture, the medium gives rise to Bragg reflection, selective in wavelength and in polarization. The characteristics of the Bragg band are tunable by acting on the following structural parameters: the pitch, the helicity sense and the helix orientation. Tuning the latter parameter produces polygonal textures (Fig. 1, center). Such a texture is made of an array of micrometer-scale polygonal cells, acting a network of microlenses with wavelength-tunable focusing properties [1]. Polygonal textures can be found in biological CLCs (for instance, multiwavelength micromirrors the cuticle of scarab beetle Chrysina gloriosa [2]). Here, we perform jointly spectral and spatial characterization of CLCs with oblique helicity through a liquid-crystal-based hyperspectral imaging (HSI), which is a compact and non-destructive technique ideally adapted to characterize mesoscopic samples, both in transmission and reflection [3]. Although liquid crystal have already been used to perform multispectral and hyperspectral imaging, they have not been, to date, the subject of an HSI study. The instrument output is an image with 512*128 pixels, each of them being spectrally resolved. Spectro-spatial properties of the polygonal texture are then measured with unprecedented spectral resolution for tilted CLCs, that is 6 nm over 400-1000nm, while conventional multispectral imaging is limited to a spectral resolution of a few tens of nanometers. Our experimental results are summarized in Fig. 1. In transmission, the mesoscopic chromatic pattern of the studied sample is recovered, and its wavelength-tunable light shaping properties are emphasized with the reconstruction of the hyperspectral datacube of a quarter of polygon. Furthermore, the reflected light analysis of a single polygon (lateral dimension below 15μm) reveals the local tilting of the CLC helical axis, that is the bulk distortion constituting the texture. The signature resides in the fine tuning of the spectral characteristics of the bandgap into the part of a polygon in which the orientation of the helix axis is spatially changing. A correlation between spatial changes and spectral changes on a mesoscopic scale is therefore made possible [4]. These results demonstrate the interest of hyperspectral imaging for the precise study of complex cholesteric components, also existing in biological samples. It thus opens many perspectives to enrich and deepen our knowledge on the fine structure of these materials. Additionally, it is found that polygonal textures may offer practical solutions in numerous applications, from secure authentication to information-enriched imaging, and, particularly, in the field of cryptography.
关键词： wavelength-tunable,Bragg reflection,polygonal textures,cholesteric liquid crystal,hyperspectral imaging
更新于2025-09-11 14:15:04
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Visible Measurement of Terahertz Power Based on Capsulized Cholesteric Liquid Crystal Film
摘要： We demonstrate a new method to detect terahertz (THz) power using a temperature-supersensitive capsulized cholesteric liquid crystal film based on the thermochromic and thermodiffusion effect, which is clearly observed. A quantitative visualization of the THz intensity up to 4.0 × 103 mW/cm2 is presented. The diameter of the color change area is linearly dependent on the THz radiation power above 0.07 mW in the steady state. Moreover, the THz power can be detected for 1 sec of radiation with a parabolic relation to the color change area. The THz power meter is robust, cost-effective, portable, and even flexible, and can be used in applications such as THz imaging, biological sensing, and inspection.
关键词： quantitative visualization,cholesteric liquid crystal,terahertz
更新于2025-09-04 15:30:14