Liquid-crystal metasurfaces: Self-assembly for versatile optical functionality

Liquid crystals subjected to modulated surface alignment assemble into metasurface-type structures capable of various flat-optical functionalities, including light diffraction and focusing, deflection and splitting. Remaining in a fluid phase, they are susceptible to external stimuli, and, in particular, can be efficiently controled by low voltages. We overview the existing approaches to the design and fabrication of liquid-crystal metasurfaces, highlight their realized optical functions and discuss the applied potential in emerging photonic devices.

Chiral Nematic Cellulose Nanocrystal Films Cooperated with Amino Acids for Tunable Optical Properties

The exploration of functional materials relies greatly on the understanding of material structures and nanotechnologies. In the present work, chiral nematic cellulose nanocrystal (CNC) films were prepared by incorporation with four types of amino acids (AAs, glycine, histidine, phenylalanine, and serine) via evaporation-induced self-assembly. The films present ideal iridescence and birefringence that can be tuned by the amount of AAs added. The intercalation of AAs enlarged the pitch values, contributing to the red-shift trend of the reflective wavelength. Among the AAs, serine presented the most compatible intercalation into cellulose crystals. Interestingly, histidine and phenylalanine composite films showed high shielding capabilities of UV light in diverse wavelength regions, exhibiting multi-optical functions. The sustainable preparation of chiral nematic CNC films may provide new strategies for materials production from biocompatible lignocellulose.

The new innovative optic complete method of identification of oil and its fraction

Development and demonstration of a new method for highly accurate forecasting of the hydrocarbon composition of oil based on determining the spectrum of its universal material constant–dielectric function, as by direct measurement using the method of spectroscopic ellipsometry, are today accepted as the world standard for determining the optical functions of any substance in a liquid or solid state, and by its quantum-mechanical calculation from first principles to complete coincidence with the measurement results. A methodology will be proposed for the complete description of any oil and the identification of it belonging to a particular oilfield. The methodology is not only universal and highly accurate, but also economical. In this work, we obtained several groups of fractions of crude oilsamples from different oil fields in Azerbaijan, which were accessed by spectroscopic ellipsometry over the 1.5–6.5 eV spectral range at room-temperature. Optical constants and dielectric function were obtained for massive samples of each substance and fractions. The proposed method is a complete dielectric fingerprint of oils for widespread use, including for environmental monitoring of oil-contaminated areas of the sea and land.

Organic pigments: general principles

This introductory chapter presents an overview of the general principles underlying the structural chemistry, manufacturing processes, and application technology of organic pigments. The coverage provides a fundamental theoretical and practical basis for the chapters that follow in this series that are devoted to specific chemical classes of industrially significant organic pigments of the azo, phthalocyanine, carbonyl, dioxazine, and metal complex classes. The initial sections cover the fundamental differences which mean that dyes and pigments are considered universally as two separate types of colorant, based on their solubility characteristics. They also provide discussions of the contrasting chemical, technological, and performance features of organic and inorganic pigments. An outline of the most important historical features in the development of the synthetic organic pigment industry is then presented, from its origins in the 19th century that followed soon after the development of the industrial synthetic dye industry, through its expansion in the 20th century, to its current position as a mature global industry. A section then follows that describes the functions that organic pigments are required to perform in their application, mainly their optical functions that include not only color properties, including hue, strength, brightness, but also the contrasting requirements for transparency or opacity as demanded by specific applications. The pigments are also required to resist the conditions and agencies that they might encounter in applications, assessed as fastness properties, such as fastness to light, heat, solvents and chemicals, amongst many others, to an extent that specific applications demand. The principles, in broad terms, of the ways in which chemical structures determine colour and performance of organic pigments are discussed, with focus not only on the influence of molecular structure, but also on the effect of the crystal structural arrangement and the particulate structure, including particle size and shape and its distribution, on application performance. This is important as these pigments are applied as a dispersion of finely divided crystalline solid particles that are insoluble and are ultimately trapped mechanically in their application medium, often a polymer. The manufacture of organic pigments is discussed in broad terms. The overall process may be considered in stages, initiated by the chemical synthetic sequence in which the pigment is formed, followed by a conditioning stage where the crude product thus obtained is modified to optimise its performance properties, and finally finishing where the product is processed into a form, or preparation, that is suitable for its intended applications. Finally, the technological principles underlying a broad range of the most important application areas for organic pigments, which are mainly in paints, inks, and plastics, are discussed.

Multifunctional wide-angle optics and lasing based on supercell metasurfaces

Metasurfaces are arrays of subwavelength spaced nanostructures that can manipulate the amplitude, phase, and polarization of light to achieve a variety of optical functions beyond the capabilities of 3D bulk optics. However, they suffer from limited performance and efficiency when multiple functions with large deflection angles are required because the non-local interactions due to optical coupling between nanostructures are not fully considered. Here we introduce a method based on supercell metasurfaces to demonstrate multiple independent optical functions at arbitrary large deflection angles with high efficiency. In one implementation the incident laser is simultaneously diffracted into Gaussian, helical and Bessel beams over a large angular range. We then demonstrate a compact wavelength-tunable external cavity laser with arbitrary beam control capabilities – including beam shaping operations and the generation of freeform holograms. Our approach paves the way to novel methods to engineer the emission of optical sources.

Multiscale Laser Written Photonic Structures in Bulk Chalcogenide Glasses for Infrared Light Transport and Extraction

Direct ultrafast laser processing is nowadays considered the most flexible technique allowing to generate complex 3D optical functions in bulk glasses. The fact that the built-in optical element is embedded in the material brings several advantages in terms of prototype stability and lifetime, but equally in terms of complexity and number of possible applications, due to the 3D design. The generated optical functions, and in particular the single mode character of the light guiding element alongside the accessibility toward different spectral windows, depend on the refractive index contrast that can be achieved within the material transparency window and on the characteristic dimensions of the optical modification. In particular, the accessibility to the infrared and mid-infrared spectral domains, and to the relevant applications in sensing and imaging, requires increasing the cross-section of the guiding element in order to obtain the desired normalized frequency. Moreover, efficient signal extraction from the transported light requires nanometer size void-like index structures. All this demands a thorough knowledge and an optimal control of the material response within the interaction with the ultrafast laser pulse. We present here an overview of some recent results concerning large-mode-area light transport and extraction in sulfur-based chalcogenide mid-infrared glasses, putting emphasis on the study of the glass response to ultrafast lasers. We then demonstrate the utilization of the achieved optimized local index modifications for building efficient and compact embedded spectrometers (linear optical functions) and saturable absorbers (nonlinear optical functions) for integrated photonic applications in the infrared and mid-infrared spectral ranges.

Biophotonic probes for bio-detection and imaging

The rapid development of biophotonics and biomedical sciences makes a high demand on photonic structures to be interfaced with biological systems that are capable of manipulating light at small scales for sensitive detection of biological signals and precise imaging of cellular structures. However, conventional photonic structures based on artificial materials (either inorganic or toxic organic) inevitably show incompatibility and invasiveness when interfacing with biological systems. The design of biophotonic probes from the abundant natural materials, particularly biological entities such as virus, cells and tissues, with the capability of multifunctional light manipulation at target sites greatly increases the biocompatibility and minimizes the invasiveness to biological microenvironment. In this review, advances in biophotonic probes for bio-detection and imaging are reviewed. We emphatically and systematically describe biological entities-based photonic probes that offer appropriate optical properties, biocompatibility, and biodegradability with different optical functions from light generation, to light transportation and light modulation. Three representative biophotonic probes, i.e., biological lasers, cell-based biophotonic waveguides and bio-microlenses, are reviewed with applications for bio-detection and imaging. Finally, perspectives on future opportunities and potential improvements of biophotonic probes are also provided.