Functional Dendrimers for Nonlinear Optics

Novel nonlinear optical (NLO) building blocks can be placed into the periphery, branch, or core of a dendrimer to construct precise molecular architecture with predetermined chemical composition. The site‐isolation effect, through the encapsulation of active moieties by dendrons, or the cooperative effect, through the coherent interaction among the same or different kinds of active blocks in the dendrimer, can greatly enhance the performance of NLO materials. This paper provides a review of recent developments in dendrimers for NLO applications, such as electro‐optics (E‐O), photorefractive (PR) materials, second harmonic generation (SHG), and two‐photon absorption (TPA).     

Photophysical and electrochemical properties of donor-acceptor conjugated oligomers based on 3,4-ethylenedioxythiophene and deficient rings

The photophysical and electrochemical properties of four novel donor-accepter (D-A) conjugated oligomers a-d based on 3,4-ethylenedioxythiophene (EDOT) and electrondeficient heterocycle rings were investigated. The UV-vis absorption spectroscopy, fluorescence emission spectroscopy and cyclic voltammertry studies suggest that the oligomers are expected to provide enhanced charge-transporting properties for the development of efficient electroluminescent materials. Furthermore, the third-order nonlinear optical (NLO) measurements made by Z-scan technique indicate that they have good third-order NLO response and are desired materias for fabricating nonlinear photonic devices. In the solid state of these oligomers, a strong tendency of self-assembled structure was also revealed by X-ray diffraction (XRD) patterns in powder.     

光致变色聚合物的光学性能与应用

综述了光致变色聚合物的光学性能及应用的近期研究进展，首先，介绍了光诱导双折射及双色现象形成机理及实验方法，并讨论了分子结构与外部条件对上述现象的影响。其次，介绍了光致变色聚合开关线性光学性能和应用。如由光助极化和全光极化形成的光开关现象将有可能引起数字存储或光-光开关等新装置的出现，最后，简单说明了光诱导表面光栅在近几年的研究情况，并分析了它们在全息图像存贮，光学过滤器及共振电偶中的潜在应用。     

Synthesis, linear and quadratic nonlinear optical properties of ionic indoline and N,N-dimethylaniline based chromophores

The synthesis, linear and second-order nonlinear optical (NLO) properties of a series of ionic indoline and N,N-dimethylaniline based chromophores are described. In order to optimise the second-order NLO response of these compounds four basic variations to the molecules and/or their environments have been implemented and their effect studied. These consist of changes to the counter-anion (from iodide to p-toluenesulfonate to naphthalene-2-sulfonate), variation of the solvent polarity [dimethyl sulfoxide (DMSO) to methanol (MeOH) to chloroform (CHCl₃)], annelation of the acceptor unit (pyridinium to quinolinium) and a change in the donor used (N,N-dimethylaniline to indoline). It is found that the strongest enhancements to the quadratic NLO response occur when the acceptor moiety is changed from pyridinium to quinolinium, while compounds with an indoline donor group are slightly superior to those containing dimethylaniline as donor. There is no real discernable change in the first hyperpolarizability on altering either the counter-anion or solvent used for the measurements. X-ray crystallographic data were obtained for two of the compounds, and they are found to pack in centrosymmetric fashion, and have a small degree of twisting between the donor and acceptor. From this data it is seen that there is a general agreement between the degree of bond-length alternation (BLA) and the NLO response of the chromophores, and that for charged chromophores such as these a BLA value of approximately 0.1 Å is optimal.     

有机光折变聚合物的设计制备研究进展

有机/聚合物光折变材料是一类在信息传输、存储及信息处理等方面有着很大发展潜力的非线性光学材料,文中介绍了有机光折变材料的几种典型应用,综述了目前研究较为深入的几类有机光折变聚合物材料的组成特征和性能特点,并对其近年来材料的设计思想和制备研究进展进行分类表述,分析了材料体系中存在的亟待解决的瓶颈问题。最后对有机光折变聚合物材料的实用性及发展方向进行了展望。     

Halide Perovskites for Nonlinear Optics

Halide perovskites provide an ideal platform for engineering highly promising semiconductor materials for a wide range of applications in optoelectronic devices, such as photovoltaics, light-emitting diodes, photodetectors, and lasers. More recently, increasing research efforts have been directed toward the nonlinear optical properties of halide perovskites because of their unique chemical and electronic properties, which are of crucial importance for advancing their applications in next-generation photonic devices. Here, the current state of the art in the field of nonlinear optics (NLO) in halide perovskite materials is reviewed. Halide perovskites are categorized into hybrid organic/inorganic and pure inorganic ones, and their second-, third-, and higher-order NLO properties are summarized. The performance of halide perovskite materials in NLO devices such as upconversion lasers and ultrafast laser modulators is analyzed. Several potential perspectives and research directions of these promising materials for nonlinear optics are presented.     

聚酰亚胺基二阶非线性光学材料

二阶非线性光学材料作为光电子中的关键材料已引起了研究人员极大的兴趣。而聚酰亚胺作为一种二阶非线性光学材料的基体除了具备有机聚合物的共有优点如易加工成型外,还比其它聚合物基二阶非线怀光学材料具有更高的玻璃化转变温度,更优异的耐热性能、电性能和机械性能,是目前被选用最多的二阶非线性光学材料的聚合物基体之一。本文对近年来聚酰亚胺基二阶非线性光学材料的制备、性能研究以及极化松驰方面的研究进展进行了评述。     

Fabrication of photonic nanostructures in nonlinear optical polymers

Two experimental techniques have been developed for creating photonic structures in nonlinear optical (NLO) polymers with precisions down to nanoscale. The first technique uses nanoimprinting technology to directly pattern the guest-host NLO polymers. It can be applied to the fabrication of photonic bandgap structures in NLO materials, as well as many other photonic structures in both linear and nonlinear polymers. The second technique utilizes self-assembly of NLO polymer monolayers onto a nanostructured template. This approach provides a highly effective means to implement practical waveguide devices using high performance self-assembled polymers with large electro-optic activity and inherent long-term stability. An optical switching device is proposed, based on nanofabricated NLO polymers.     

Photorefractive Polymers and Composites

Materials demonstrating a photorefractive effect are principal candidates for numerous applications, including high-density optical data storage, optical image processing, phase conjugated mirrors and lasers, dynamic holography, optical computing, pattern recognition, etc. Considerable progress has been made in the research on photorefractive polymers and composite materials in the last few years. These materials have many advantages over inorganic photorefractive crystals, including large optical nonlinearities, low dielectric constants, low cost and ease of fabrication. A large number of materials, including those exhibiting an extremely large photorefractive effect, have been developed. In addition, a number of interesting phenomena particular to polymeric photorefractive materials have been reported and corresponding mechanisms have been proposed to account for these phenomena. Possible applications of these materials have been explored with the demonstration of a volume holographic storage device based on photorefractive polymers. This paper reviews the latest developments of the young and exciting field of polymeric photorefractive materials.     

非线性光学聚合物材料的研究进展

非线性光学聚合物是新型的具有很高实用价值的功能材料，在光电子信息领域具有广阔的应用前景。文中简要介绍了非线性光学理论和极化原理，综述了非线性光学聚合物材料的研究现状及进展，首重阐述了掺杂型、侧主链型、交联型及共轭型等非线性光学聚合物的结构与性能，展望了今后的研究方向。     

Nonlinear optical properties and performance optimization of the pro-aromatic chromophores for NLO materials

Geometric structures and nonlinear optical properties (NLO) of the pro-aromatic chromophores, comprising indoline moiety as an electron donor and azo linker as a π-conjugated bridge, have been investigated by means of quantum chemistry method and the response theory. Three solvent models were used to study the short-range interaction and long-range interaction between solvent and solution in order to simulate the experimental spectra. Simulated absorption used by the polarizable continuum model gave a well agreement with experimental measurement. The micro-mechanisms of first hyperpolarizability were explained on the basis of the two-level models, and charge difference density methods demonstrated that the chromophore (4f), which indoline moiety acts as an electron donor and N,N-dimethyl formamide as an acceptor bridged by azo bridge, displays an efficient intramolecular charge transfer properties amplifying the NLO response. Calculations of two-photon absorption (TPA) for the indoline chromophore were performed to develop their potential application on TPA materials. Additionally, some molecules were designed by replacing electron donor and introducing additional heteroatoms to tune the NLO parameters. The results show 4f-a with 1,4-phenylenediamine donor unit and introducing one heteroatom display well NLO character.     

Metal–organic frameworks for electronics: emerging second order nonlinear optical and dielectric materials

Abstract

Metal–organic frameworks (MOFs) have been intensively studied over the past decade because they represent a new category of hybrid inorganic–organic materials with extensive surface areas, ultrahigh porosity, along with the extraordinary tailorability of structure, shape and dimensions. In this highlight, we summarize the current state of MOF research and report on structure–property relationships for nonlinear optical (NLO) and dielectric applications. We focus on the design principles and structural elements needed to develop potential NLO and low dielectric (low-κ) MOFs with an emphasis on enhancing material performance. In addition, we highlight experimental evidence for the design of devices for low-dielectric applications. These results motivate us to develop better low-dielectric and NLO materials and to perform in-depth studies related to deposition techniques, patterning and the mechanical performance of these materials in the future.     

Metal–organic frameworks for electronics: emerging second order nonlinear optical and dielectric materials

Metal–organic frameworks (MOFs) have been intensively studied over the past decade because they represent a new category of hybrid inorganic–organic materials with extensive surface areas, ultrahigh porosity, along with the extraordinary tailorability of structure, shape and dimensions. In this highlight, we summarize the current state of MOF research and report on structure–property relationships for nonlinear optical (NLO) and dielectric applications. We focus on the design principles and structural elements needed to develop potential NLO and low dielectric (low-κ) MOFs with an emphasis on enhancing material performance. In addition, we highlight experimental evidence for the design of devices for low-dielectric applications. These results motivate us to develop better low-dielectric and NLO materials and to perform in-depth studies related to deposition techniques, patterning and the mechanical performance of these materials in the future.     

Spectroscopic and nonlinear photophysical characterization of organic octupolar-compounds supported by anodic-alumina nanotube-arrays

Amorphous anodic alumina membranes (AAM) comprising highly ordered nanometric porous arrays (porous anodic aluminas: PAA) with 1D-nanotube dimensions of ∼75 nm in diameter and 45 microns in depth were successfully prepared and used as nanostructured host networks for different functionalized octupolar chromophores (named here Oct-(n)). Atomic force microscopy (AFM) studies performed on the developed hybrid systems confirmed a homogeneous insertion of these organic molecules into the PAA nanotube-arrays. Samples with high structural quality were selected for several photophysical characterizations: Comprehensive X-ray diffraction (XRD) and optical spectroscopic characterizations performed according to UV-vis absorption, photoluminescent (PL) and Raman measurements revealed the structural and optical performance of these molecules within the PAA-confinement. Since the implemented optical chromophores were specifically functionalized for nonlinear optical (NLO) applications, the obtained Oct-(n)/PAA-based amorphous hybrids were also characterized according to cubic NLO-techniques such as third harmonic generation (THG) and the Z-Scan method. PAA-confined octupolar chromophores have shown interesting linear and NLO optical properties which have not yet been intensively investigated in bulk hybrid systems; hence, the obtained hybrid nanostructures represent a promising field of investigation in the route to functional octupolar-based materials, where different self-assembled molecular structures may be formed, giving rise to enhanced linear and NLO-properties.     

Enhanced third-order nonlinear optical properties in dendrimer-metal nanocomposites

Nonlinear optical (NLO) and time-resolved fluorescence spectroscopic measurements of dendrimer-metal nanocomposites (DNCs) are reported. Third-order NLO effects were investigated by degenerate four-wave mixing (DFWM) measurements for DNCs and DNCs incorporated into thin polymeric films. The results show an enhancement of the third-order nonlinear susceptibility for the chromophore-functionalized dendrimer-metal nanocomposites. Investigations of the mechanism of the enhanced NLO effect suggested a strong contribution because of the metal's local field. These results show the potential usefulness of dendrimer-metal nanocomposites for nonlinear optical effects and biophotonic applications.     

Optimization of optical limiting devices based on excited-state absorption

Limiting devices protect sensitive optical elements from laser-induced damage (LID). Passive devices use focusing optics to concentrate the light through a nonlinear optical (NLO) element (or elements) to reduce the limiting threshold. Unfortunately, these NLO elements may themselves undergo LID for high inputs, restricting the useful dynamic range (DR). Recently, efforts at optimizing this DR have focused on distributing the NLO material along the propagation path z of a focused beam, resulting in different portions of the device (in z) exhibiting NLO response at different inputs. For example, nonlinear absorbers closer to the lens, i.e., upstream, protect device elements downstream near the focal plane. This results in an undesirable increase in the threshold, although the lowest threshold is always obtained with the final element at focus. Thus there is a compromise between DR and threshold. This compromise is determined by the material. We concentrate on reverse saturable absorber (RSA) materials (molecules exhibiting larger excited-state than ground-state absorption). We look at both tandem devices and devices in which the concentration of the NLO material is allowed to spatially vary in z. These latter devices require solid-state hosts. The damage threshold of currently available solid-state hosts is too low to allow known RSA materials to reach their maximum absorption, which occurs when all molecules are in their excited state. This is demonstrated by approximate analytical methods as well as by a full numerical solution of the nonlinear wave propagation equation over extremely large distances in z (up to 10(3)Z(0), where Z(0) is the Rayleigh range of the focused beam). The numerical calculations, based on a one-dimensional fast Fourier transform, indicate that proper inclusion of diffraction reduces the effectiveness of reverse saturable absorption for limiting, sometimes by more than a factor of 10. Liquid-based devices have higher damage thresholds (damage occurs to the cuvette wall) and, thus, larger nonlinear absorption. However, RSA material in liquid hosts may suffer from larger thermal lensing.     

Optical Properties of Functional Hybrid Organic–Inorganic Nanocomposites

Functional hybrids are nanocomposite materials lying at the interface of organic and inorganic realms, whose high versatility offers a wide range of possibilities to elaborate tailor‐made materials in terms of chemical and physical properties. Because they present several advantages for designing materials for optical applications (versatile and relatively facile chemistry, easy shaping and patterning, materials having good mechanical integrity and excellent optical quality), numerous silica or/and siloxane based hybrid organic–inorganic materials have been developed in the past few years. The most striking examples of functional hybrids exhibiting emission properties (solid‐state dye lasers, rare‐earth doped hybrids, electroluminescent devices), absorption properties (photochromic), nonlinear optical (NLO) properties (second‐order NLO properties, photochemical hole burning (PHB), photorefractivity), and sensing are summarized in this review.     

有机吡啶盐分子在非线性光学领域中的应用

本文从分子工程和材料工程的角度介绍了有机吡啶盐及其衍生物在非线性光学中的应用。有机吡啶盐分子由于独特的化学结构,除了具有较大的分子超极化率外,其分子设计上的灵活性和功能上的多样性,使其在非线性光学材料领域占有重要的一筑之地。同时该类体系多种多样的组装形式也极大地丰富了非线性光学材料的种类。     

Adaptive optical array receivers for detection of surface acoustic waves

Adaptive interferometric detection systems based on two-wave mixing in photorefractive crystals have been configured as distributed optical receivers. The spatial distribution of the detection laser power on the sample surface is controlled by use of phase gratings and amplitude masks. The responses of point, line, array, and chirped optical receivers to propagating surface acoustic waves (SAW's) are discussed theoretically and demonstrated experimentally. It is shown that by use of different object beam footprints it is possible to configure adaptive holographic SAW receivers that are either broadband or narrow band and that are preferentially sensitive to SAW's propagating in given directions. The receivers also allow for the distribution of laser power over the sample, eliminating the excessive heating or surface damage that can occur in some materials when high power, point-focused, detection lasers are used.     

Synthesis and the third-order non-linear optical properties of new azobenzene-containing side-chain polymers

A new series of aromatic azobenzol compounds containing vinyl have been designed as monomers. The azobenzene-containing side-chain polymers containing azo NLO chromophore in each side chain have been synthesized via free radical polymerization. FT-IR, elemental analysis and ¹H NMR were performed to characterize the azo monomers. The molecular weight of the polymers and their distribution were determined by gel permeation chromatography (GPC). The third-order NLO coefficient of azo monomers and their polymers were measured by degenerated four wave mixing (DFWM) technique. As a result, the enhancement of the molecular conjugation and the increase of the NLO chromophore concentration in the molecular chain contribute much to heightening the third-order NLO effect. The electronic effect of substituent on the azobenzol group and the push–pull electronic structure contributes much to enhancing the NLO property.