Thierry Verbiest

Second-order nonlinear optical materials: recent advances in chromophore design

This paper deals with recent and important developments in the field of organic materials for second-order nonlinear optics. Attention is drawn to current trends in chromophore design with a discussion of current progress and problems in this field. A number of important classes of chromophores, such as one-dimensional charge-transfer molecules, octopolar compounds, ionic materials, multichromophore systems and organometallics, are discussed.

Chirality and Chiroptical Effects in Plasmonic Nanostructures: Fundamentals, Recent Progress, and Outlook

Strong chiroptical effects recently reported result from the interaction of light with chiral plasmonic nanostructures. Such nanostructures can be used to enhance the chiroptical response of chiral molecules and could also significantly increase the enantiomeric excess of direct asymmetric synthesis and catalysis. Moreover, in optical metamaterials, chirality leads to negative refractive index and all the promising applications thereof. In this Progress Report, we highlight four different strategies which have been used to achieve giant chiroptical effects in chiral nanostructures. These strategies consecutively highlight the importance of chirality in the nanostructures (for linear and nonlinear chiroptical effects), in the experimental setup and in the light itself. Because, in the future, manipulating chirality will play an important role, we present two examples of chiral switches. Whereas in the first one, switching the chirality of incoming light causes a reversal of the handedness in the nanostructures, in the second one, switching the handedness of the nanostructures causes a reversal in the chirality of outgoing light.

Supramolecular Second-Order Nonlinearity of Polymers with Orientationally Correlated Chromophores

Nonlinear optical chromophores can be organized as orientationally correlated side groups of polymers with a rigid backbone. In such an organization, each chromophore contributes coherently to the second-order nonlinear response of the polymer structure. A first hyperpolarizability exceeding 5000 × 10−30 electrostatic units was measured for a poly(isocyanide) structure containing ∼100 chromophores by means of hyper-Rayleigh scattering. Electric field-induced second-harmonic generation measurements confirmed that the product of the permanent dipole moment and the first hyperpolarizability was enhanced for the polymer structure. These results provide guidelines for future efforts to optimize supramolecular structures for applications in second-order nonlinear optics.

Second-order Nonlinear Optical Characterization Techniques : An Introduction

General Aspects of Second-Order Nonlinear Optics Linear optical phenomena Nonlinear optical phenomena Examples of nonlinear optical phenomena Symmetries in second-order nonlinear optics Second-order polarizabilities and susceptibilities Beyond the electric-dipole approximation Determination of Molecular Symmetry with Hyper-Rayleigh Scattering Hyper-Rayleigh scattering: general principles Experimental techniques and equipment Determination of molecular symmetries Switching the first hyperpolarizability at the molecular level Probing aggregation and supramolecular structure in solution Characterization of Interfaces, Surfaces, and Thin Films Second-harmonic generation and sum-frequency generation from surfaces: general principles Experimental techniques and equipment Probing the symmetry of interfaces, surfaces, and thin films Molecular orientation at surfaces Surface adsorption and surface reactions Characterization of Surface Chirality by Second-Harmonic Generation and Sum-Frequency Generation Chirality and second-order nonlinear optics: general principles Experimental procedures Second-harmonic generation in nanostructures Applications to biological systems Molecular origin Relation with the Faraday effect Second-Order Nonlinear Optical Imaging Techniques General principles Experimental techniques and equipment Applications Appendix Index References appear at the end of each chapter.

Nonlinear Optical Properties of Proteins Measured by Hyper-Rayleigh Scattering in Solution

Hyper-Rayleigh scattering has been used to determine the nonlinear optical properties of a chromophore-containing protein in solution. Because the technique of hyper-Rayleigh scattering allows the measurement of hyperpolarizabilities in an isotropic solution without the application of an electric field, this method is ideally suited for the study of proteins that carry a net charge. The observed orientational correlation between the nonlinear optical chromophores in incompletely solubilized protein molecules suggests that guidelines from protein structures can be used for the engineering of supramolecular structures with high optical nonlinearity.

Redox-Switching of Nonlinear Optical Behavior in Langmuir−Blodgett Thin Films Containing a Ruthenium(II) Ammine Complex

Alternating Langmuir−Blodgett multilayers containing a metal-to-ligand charge-transfer chromophore based on {RuII(NH3)5}2+ show redox-switching of the second harmonic generation from a 1064 nm laser.

Second‐harmonic generation from chiral surfaces

We present a theory of second‐harmonic generation from chiral surfaces including contributions of electric and magnetic dipole transitions to the surface nonlinearity. The nonlinear polarization and magnetization of the surface as well as the second‐harmonic fields that are radiated in the reflected and transmitted directions are expressed in terms of the six possible bilinear combinations of the components of the electric field of the fundamental beam. For the case in which the polarization of the fundamental beam is controlled by means of a quarter‐wave plate between p‐polarized linear and left‐ and right‐hand circular, the second‐harmonic fields can be expanded in terms of only three different functions of the rotation angle of the wave plate. The process exhibits nonlinear optical activity, i.e., it responds differently to the two circular polarizations of the fundamental beam if the phases of certain expansion coefficients are different. The theory is used to explain the results of a recent experimen...

Second-order non-linear optical polymers

In this article we discuss the state of the art in the field of second-order non-linear optical polymers. More specifically, we highlight those results that we think made an important contribution to the field, combined with some of our own results. We start with a general overview of all the aspects involved in characterizing second-order non-linear optical polymers, from thin film formation and poling to second-harmonic generation and electro-optic measurements on such systems. Next, we review the second-order non-linear optical properties of selected polymer systems such as poly(vinyl ether)s, polystyrenes, polymethacrylates, main-chain polymers and high Tg polymers like polyimides and polymaleimides. Finally, we discuss some new polymer systems that might become important in the field of non-linear optics in the near future.

Fast and accurate peanut allergen detection with nanobead enhanced optical fiber SPR biosensor

This paper is the first report of a fiber optic SPR biosensor with nanobead signal enhancement. We evaluated the system with a bioassay for the fast and accurate detection of peanut allergens in complex food matrices. Three approaches of an immunoassay to detect Ara h1 peanut allergens in chocolate candy bars were compared; a label-free assay, a secondary antibody sandwich assay and a nanobead enhanced assay. Although label-free detection is the most convenient, our results illustrate that functionalized nanobeads can offer a refined solution to improve the fiber SPR detection limit. By applying magnetite nanoparticles as a secondary label, the detection limit of the SPR bioassay for Ara h1 was improved by two orders of magnitude from 9 to 0.09 μg/mL. The super paramagnetic character of the nanoparticles ensured easy handling. The SPR fibers could be regenerated easily and one fiber could be reused for up to 35 times without loss of sensitivity. The results were benchmarked against a commercially available polyclonal ELISA kit. An excellent correlation was found between the Ara h1 concentrations obtained with the ELISA and the concentrations measured with the SPR fiber assay. In addition, with the SPR fiber we could measure the samples twice as fast as compared to the fastest ELISA protocol. Since the dipstick fiber has no need for microchannels that can become clogged, time consuming rinsing step could be avoided. The linear dynamic range of the presented sensor was between 0.1 and 2 μg/mL, which is considerably larger than the ELISA benchmark.

Selective Uptake of Rare Earths from Aqueous Solutions by EDTA-Functionalized Magnetic and Nonmagnetic Nanoparticles

Magnetic (Fe3O4) and nonmagnetic (SiO2 and TiO2) nanoparticles were decorated on their surface with N-[(3-trimethoxysilyl)propyl]ethylenediamine triacetic acid (TMS-EDTA). The aim was to investigate the influence of the substrate on the behavior of these immobilized metal coordinating groups. The nanoparticles functionalized with TMS-EDTA were used for the adsorption and separation of trivalent rare-earth ions from aqueous solutions. The general adsorption capacity of the nanoparticles was very high (100 to 400 mg/g) due to their large surface area. The heavy rare-earth ions are known to have a higher affinity for the coordinating groups than the light rare-earth ions but an additional difference in selectivity was observed between the different nanoparticles. The separation of pairs of rare-earth ions was found to be dependent on the substrate, namely the density of EDTA groups on the surface. The observation that sterical hindrance (or crowding) of immobilized ligands influences the selectivity could provide a new tool for the fine-tuning of the coordination ability of traditional chelating ligands.