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In molecular rotors, a type of molecular machine, spontaneous rotors without the need for an external stimulus are promising because conventional molecular rotors require a continuous energy supply. In this study, we demonstrate spontaneous transformation from kinetically favored metastable right-handed helical aggregates to thermodynamically stable left-handed helical aggregates after an evaporation procedure. In addition, we propose the conditions for preparation of metastable right-handed helical aggregates, whose chirality can be spontaneously inverted, based on kinetic analysis. This molecular power spring will be useful for designing new types of molecular machines.

We demonstrate the evaporation rate-based selection of supramolecular chirality for the first time. P-type aggregates prepared by fast evaporation, and M-type aggregates prepared by slow evaporation are kinetic and thermodynamic products under dynamic reaction conditions, respectively. These findings provide a novel solution reaction chemistry under the dynamic reaction conditions.

The influence of the regioregularity on the second-order nonlinear optical response of polythiophenes in solution was investigated. A series of chiral poly((S)-3,7- dimethyloctylthiophene)s with va...

Three-dimensionally ordered macroporous materials have unique structural and optical properties, making them useful for numerous applications in catalysis, membrane science, and optics. Accessible and economic fabrication of these materials is essential to fully explore the many possibilities that these materials present. A new templating method to fabricate three-dimensionally ordered macroporous materials without overlayers is presented. The resulting structures are freestanding inverse opals with large-area uniformity. The versatility and power of our fabrication method is demonstrated by synthesizing inverse opals displaying fluorescence, chirality, upconversion, second harmonic generation, and third harmonic generation. This economical and versatile fabrication method will facilitate research on inverse opals in general and on linear and nonlinear optical effects in 3D photonic crystals specifically. The relative ease of synthesis and wide variety of resulting materials will help the characterization and improvement of existing anomalous dispersion effects in these structures, while providing a platform for the discovery and demonstration of novel effects.

Rare earth atoms exhibit several interesting properties, for example, large magnetic moments and luminescence. Introducing these atoms into a different matrix can lead to a material that shows multiple interesting effects. Holmium atoms were incorporated into an iron oxide nanoparticle and the concentration of the dopant atom was changed in order to determine its influence on the host crystal. Its magnetic and magneto-optical properties were investigated by vibrating sample magnetometry and Faraday rotation measurements. The luminescent characteristics of the material, in solution and incorporated in a polymer thin film, were probed by fluorescence experiments. ispartof: Materials vol:7 issue:2 pages:1155-1164 ispartof: location:Switzerland status: published

An achromatic component shares a common focus at two wavelengths and is a commonly used device in optical assemblies. This work explores the cost versus performance tradeoff for several types of achromatic lenses: conventional doublets with homogenous glass elements, hybrid doublets with a diffractive surface, axial GRadient INdex (GRIN) lenses (where the index of refraction changes along the length of the lens), and radial GRIN lenses (where the index of refraction changes depending on radial position). First order achromatic principles will be reviewed and applied to each system as a starting point and refined through the use of ray trace software. Optical performance will be assessed in terms of focusing efficiency and imaging. Cost will then be evaluated by accounting for current manufacturing costs and retail price through several distributors.

We studied the adsorption kinetics of supported ultrathin films of dye-labeled polystyrene (l-PS) by combining dielectric spectroscopy (DS) and the interface-specific nonlinear optical second harmonic generation (SHG) technique. While DS is sensitive to the fraction of mobile dye moieties (chromophores), the SHG signal probes their anisotropic orientation. Time-resolved measurements were performed above the glass transition temperature on two different sample geometries. In one configuration, the l-PS layer is placed in contact with the aluminum surface, while in the other one, the deposition is done on a strongly adsorbed layer of neat PS. From the time dependence of the dielectric strength and SHG signal of the l-PS layer in contact with the metal, we detected two different kinetics regimes. We interpret these regimes in terms of the interplay between adsorption and orientation of the adsorbing labeling moieties. At early times, dye moieties get adsorbed adopting an orientation parallel to the surface. When adsorption proceeds to completeness, the kinetics slows down and the dye moieties progressively orient normal to the surface. Conversely, when the layer of l-PS layer is deposited on the strongly adsorbed layer of neat PS, both the dielectric strength and the SHG signal do not show any variation with time. This means that no adsorption takes place.

Recently, much research has been performed on developing low-bandgap polymers for e.g. harvesting solar energy. In the quest to improve these properties, little attention has been paid to their nonlinear optical properties, despite their interesting linear optical spectra and structural similarities to certain nonlinear optically active compounds. We characterized the optical second harmonic generation of corona poled films of poly(cyclopenta[2,1-b;3,4-b′] dithiophen-4-ylidenedioctylmalonate). The unexpectedly large nonlinear optical susceptibilities and the thermal and temporal stability of the material compare favorably to other novel nonlinear optical materials despite the lack of a donor-acceptor dye. Additionally, the polymer displays a very low absorption in the relevant wavelength region. These results demonstrate the promise of these materials for nonlinear optical devices. publisher: Elsevier articletitle: Optical second harmonic generation in a low-bandgap polymer journaltitle: Materials Chemistry and Physics articlelink: http://dx.doi.org/10.1016/j.matchemphys.2014.06.003 content_type: article copyright: Copyright © 2014 Elsevier B.V. All rights reserved. ispartof: Materials Chemistry and Physics vol:147 issue:3 pages:356-359 status: published

Recent research has focused on developing low-bandgap polymers for harvesting solar energy, fine-tuning desirable properties including power conversion efficiency, carrier mobilities and broad light absorption. However, little attention has been paid to their nonlinear optical properties. We characterized the optical second harmonic generation of corona poled films of poly(cyclopenta[2,1-b;3,4-b']dithiophen-4-ylidenedioctylmalonate). Despite being amorphous and lacking a typical donor-acceptor dye, these films display large nonlinear optical susceptibilities. Coupled with their stability and low absorption in the relevant wavelength region, these polymer films compare favorably to other materials. Our results show the promise of low-bandgap polymers for nonlinear optical applications.

In light of the population aging in many developed countries, there is a great economical interest in improving the speed and cost-efficiency of healthcare. Clinical diagnosis tools are key to these improvements, with biophotonics providing a means to achieve them. Standard optical microscopy of in vitro biological samples has been an important diagnosis tool since the invention of the microscope, with well known resolution limits. Nonlinear optical imaging improves on the resolution limits of linear microscopy, while providing higher contrast images and a greater penetration depth due to the red-shifted incident light compared to standard optical microscopy. It also provides information on molecular orientation and chirality. Adaptive optics can improve the quality of nonlinear optical images. We analyzed the effect of sensorless adaptive optics on the quality of the nonlinear optical images of biological samples. We demonstrate that care needs to be taken when using a large field of view. Our findings provide information on how to improve the quality of nonlinear optical imaging, and can be generalized to other in vitro biological samples. The image quality improvements achieved by adaptive optics should help speed up clinical diagnostics in vitro, while increasing their accuracy and helping decrease detection limits. The same principles apply to in vivo biological samples, and in the future it may be possible to extend these findings to other nonlinear optical effects used in biological imaging. ispartof: Proceedings of SPIE ispartof: Biophotonics: Photonic Solutions for Better Health Care IV vol:9129 ispartof: Photonics Europe location:Brussels, Belgium date:8 May - 8 May 2014 status: published

Three-dimensionally (3D) ordered macroporous materials combine interesting structural and optical properties. Accessible and economic fabrication is essential to fully explore the unique possibilities these materials present. A common method to fabricate 3D ordered macroporous materials is by self-assembling colloids, resulting in so-called opals. A templating strategy is then often used to introduce additional functionality inside the porous structure, giving rise to inverse opals. In this work, we developed an easy and versatile method to fabricate highly uniform polymer inverse opals without overlayers. Briefly, our approach consists of sandwiching a resin melt between two opal templates, forcing all material inside or between the macroporous structures. The opal voids are fully filled and the superfluous melt material is extruded before curing the resin. Finally, the opal templates are removed by chemical etching. The resulting structures are freestanding 3D macroporous films with large-area uniformity, displaying strong photonic properties due to their structural order. Additionally, many applications require specific optical functionalities. The versatility of our templating method is uniquely suited for this purpose as it allows doping of the melt before infiltration. Therefore, we can incorporate a large variety of optical functions in the inverse opals using a single approach We believe this method will help the systematic investigation and improvement of existing effects in these structures, while providing a platform for the discovery and demonstration of novel effects. As this method combines 3D ordered macroporous materials with linear and nonlinear optical materials, it is even possible to tune optical interactions, which could be technologically relevant for OLEDs, solar cells, lasers, electro-optical modulators and optical switches.

Circular dichroism in optical second harmonic generation (CD-SHG) is studied in planar symmetrical arrays of G-shaped and mirror-G-shaped nanostructures. Anisotropic CD-SHG measurements demonstrate a strong dependence of the value and the sign of the CD effect on the angle of incidence of the fundamental radiation. We show that both dipole and higher order multipole components of the second order susceptibility are responsible for the CD response from G-shaped nanostructures. ispartof: Physical Review B, Condensed Matter and Materials Physics vol:89 issue:12 status: published

A Certified Reference Material (CRM) for determination of aromatic hydrocarbons in air was developed. The CRM 562 consists of aromatic hydrocarbons sorbed on charcoal in glass tubes. Initial feasibility studies established that a homogeneous and stable batch could be prepared. Three intercomparisons prior to the certification allowed the identification of various sources of error. Then, a batch of about 3000 tubes was charged and certified on the basis of analyses carried out in 15 European laboratories. The preparation of the reference material and the results of the certification exercise is described. An overview on the analytical techniques used and the quality control guidelines are also presented. The certified values are 15.0 ± 0.4 μg benzene, 147.3 ± 3.8 μg toluene, 96.4 ± 2.5 μg m-xylene and 93.0 ± 2.9 μg o-xylene per tube. This reference material is recommended for quality control of measurements in the field of occupational hygiene.

Regioregular poly(3-hexylthiophene)s with chain lengths varying from 5 to 100 monomers are synthesized. Poly(3-hexylthiophene)s show in solution an unexpectedly significant second-order nonlinear optical response. The increase in transition dipole moment upon oligomerisation causes the significant second-order nonlinear optical response. crosscheck: This document is CrossCheck deposited related_data: Supplementary Information copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: The accepted version of this article will be made freely available after a 12 month embargo period history: Received 22 October 2013; Accepted 16 January 2014; Accepted Manuscript published 16 January 2014; Advance Article published 30 January 2014; Version of Record published 13 February 2014 ispartof: Chemical Communications vol:50 issue:21 pages:2741-2743 ispartof: location:England status: published

Modifying and detecting the polarization of light is increasingly important in many contexts such as Faraday isolators and electro-optical modulators. In order to control the polarization of light, it is necessary to know the polarization characteristics of the materials used in the applications. To be able to (magneto-)optically characterize novel materials, we designed a setup using a single photoelastic modulator (PEM) to simultaneously detect natural and magnetic circular dichroism and circular birefringence over a large spectral range. We then theoretically analyzed and experimentally characterized the effect of non-idealities in the PEM on the setup and the resulting data. Our results demonstrate an influence of PEM non-idealities on the measured signals, resulting in non-negligible mixing of circular birefringence and circular dichroism signals. Our measurements of the wavelength dependence of these non-idealities reveal larger non-idealities towards shorter wavelengths. These results illustrate the necessity to take PEM non-idealities into account when working with PEMs, especially at shorter wavelengths or when dealing with signals spanning different orders of magnitude. PEM non-idealities, while frequently neglected in experimental setup design and theoretical derivations, are expected to be more complicated and possibly exert a larger influence on obtained results for experimental setups with multiple PEMs. ispartof: pages:88730- ispartof: Proc. SPIE 8873 vol:88730 pages:88730- ispartof: Optics and Photonics location:San Diego, California, United States date:25 Aug - 25 Aug 2013 status: published

Circularly polarized optical second harmonic generation (SHG) is studied experimentally in regular arrays of planar G-shaped nanostructures. Circular dichroism in SHG is observed and the sign of the effect reverses with the handedness of the nanostructures, which is a signature of chirality in the nonlinear optical response.

We describe a technique to optically characterize superparamagnetism. Faraday rotation measurements are performed on a superparamagnetic nanocomposite using small alternating current magnetic fields. The superparamagnetism of the iron oxide nanoparticles causes signals at the uneven harmonics of the magnetic field frequency. These signals provide information on the magnetic moment of the superparamagnetic nanoparticles. Dia- and paramagnetism do not cause signals at higher harmonics, resulting in a high sensitivity to superparamagnetism, even in samples with large dia- or paramagnetic contributions. This technique provides a rapid, economical method to characterize superparamagnetism in composite samples not easily accessible by other techniques. ispartof: Applied Physics Letters vol:102 issue:16 pages:161903-161903 status: published

Second harmonic generation microscopy has recently become an important tool for studying materials. In this article, we use a recently developed analytical method, for second-harmonic generation microscopy, to determine the point group symmetry of micro crystals of enantiomerically pure 1,1’-bi-2-naphtol. ispartof: pages:87701- ispartof: 17TH INTERNATIONAL SCHOOL ON QUANTUM ELECTRONICS: LASER PHYSICS AND APPLICATIONS vol:8770 pages:87701- ispartof: 17th International School on Quantum Electronics - Laser Physics and Applications (ISQE) location:Nessebar: BULGARIA date:24 Sep - 28 Sep 2012 status: published

Faraday rotation, the rotation of the polarization of light due to a magnetic field in the direction of propagation of the light, is used in applications ranging from quantum memory to the detection of biomagnetic fields. For these applications large Faraday rotation is necessary, but absorption of light is detrimental. In search of these properties, we have characterized the Verdet constant of a so far unexplored class of mesogenic organic molecules. We report their spectra and provide an interpretation. A Verdet constant of almost 2.5 × 105 deg T–1 m–1 is found around 520 nm. This Verdet constant is 3 orders of magnitude larger than the largest known for organic molecules in a region without spectral features. We attribute this enormous Faraday rotation to resonant enhancement by a triplet excitation that does not appear in the linear absorption spectrum and to near-resonant enhancement by low-energy singlet excitations. Furthermore we are able to switch the Faraday rotation by changing the liquid crystal phase of the compound. These results demonstrate a new class of Faraday rotating materials with great potential to replace current materials and improve existing applications. The inherent flexibility in the synthesis of this class of molecules opens a new field of research in Faraday rotation. ispartof: Chemistry of Materials vol:25 issue:7 pages:1139-1143 status: published

Clusters of iron oxide and gold nanoparticles dispersed in a polymer show Langevin behavior in magnetization-induced second harmonic generation measurements. Contrary to Faraday rotation, the Faraday ellipticity spectrum shows a feature near the plasmon wavelength.

Circularly polarized light imparts a sense of rotation on the electron density in ring-shaped gold nanostructures. As a consequence, the near-field enhancement becomes homogeneous on the surface of the nanostructures, thereby increasing the opportunity for interaction with molecules. This type of nanostructured samples can find a broad range of applications in chemical processes where the interaction between molecules and local field enhancements play an important role. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. ispartof: Advanced Materials vol:24 issue:35 pages:OP208-OP215 ispartof: location:Germany status: published

In this work we present measurements of the switching of the Faraday effect in metal-organic compounds. Faraday rotation is the rotation of the plane of polarization of linearly polarized light under the influence of a magnetic field in the direction of propagation of the light. It is the magnetic equivalent of circular birefringence and is related to magnetic circular dichroism via the Kramers-Kronig transformation. The Faraday effect is used in optical isolators and magnetic sensors. Faraday rotation and magnetic circular dichroism spectra have been calculated and measured for various nanoparticles, nanocomposites, magnetic fluids and metal-organic complexes. These measurements and calculations indicate that it is possible to change the magneto-optical response by changing the state of the molecule, such as a change in protonation or oxidation state. The molecular environment also influences the magneto-optical spectra of metal-organic complexes and organic molecules. Thus it is possible to change the Faraday rotation spectrum by modifying the molecular environment or the molecule itself. We have measured the reversible switching of the magneto-optical response by these principles. This easily induced reversible switching opens the possibility of new devices such as switchable optical isolators.

Magneto-optically active organic compounds are of great technological interest. In contrast to inorganic materials, used in most current applications, organic materials have the advantages of fast response times, easy processing, low cost and abundant resources of starting materials available. Conjugated organic molecules or polymers have been reported to be eligible candidates for exhibiting magneto-optical responses. As part of an ongoing search in our group for efficient magneto-optical materials, eight organic conjugated dyes were screened for their Faraday rotation responses. Based on the obtained preliminary results, it is expected that planar, efficiently pi-conjugated molecules have a higher chance for exhibiting significant magneto-optical responses. Further research will be undertaken to confirm this hypothesis. ispartof: pages:1- ispartof: Nonlinear optics and applications vi vol:8434 pages:1- ispartof: Conference on Nonlinear Optics and Applications VI Brussels, BELGIUM, APR 16-18, 2012 location:Brussels date:16 Apr - 18 Apr 2012 status: published

We have measured the magnetization-induced second harmonic generation (MSHG) of a nanocomposite consisting of iron oxide nanoparticles in a polymer film. The existing theoretical framework is extended to include DC magnetic fields in order to characterize the MSHG signal and analyze the measurements. Additionally, magnetic hysteresis loops are measured for four principal polarizer-analyzer configurations, revealing the P-IN-P-OUT and S-IN-P-OUT polarizer-analyzer configurations to be sensitive to the transverse magnetic field. These results demonstrate the use of MSHG and the applied formalism as a tool to study magnetic nanoparticles and their magnetic properties. (C) 2012 Optical Society of America ispartof: Applied optics vol:51 issue:2 pages:209-213 ispartof: location:United States status: published

While it has been demonstrated that, above its resolution limit, Second Harmonic Generation (SHG) microscopy can map chiral local field enhancements, below that limit, structural defects were found to play a major role. Here we show that, even below the resolution limit, the contributions from chiral local field enhancements to the SHG signal can dominate over those by structural defects. We report highly homogeneous SHG micrographs of star-shaped gold nanostructures, where the SHG circular dichroism effect is clearly visible from virtually every single nanostructure. Most likely, size and geometry determine the dominant contributions to the SHG signal in nanostructured systems. (C) 2011 Optical Society of America ispartof: Optics Express vol:20 issue:1 pages:256-264 ispartof: location:United States status: published

A homogeneous and stable reference material consisting of aromatic hydrocarbons sorbed on Tenax in stainless-steel sample tubes has been prepared and certified. An initial feasibility trial established that a homogeneous and stable batch could be prepared. Part of this batch was used in an intercomparison, which allowed the identification of various sources of error. A second test batch was used in a second intercomparison in an attempt to improve the analytical performance of the participating laboratories. A third batch (of 1000 tubes) was then prepared and certified on the basis of analyses carried out in ten laboratories. The certified values for benzene, toluene and m-xylene are, respectively, 1.053 ± 0.014, 1.125 ± 0.015 and 1.043 ± 0.015 µg per tube. This Community Bureau of Reference (BCR) Certified Reference Material 112 is recommended for quality control and for calibration purposes.

The intense laser power required to measure nonlinear effects can damage the structures upon measuring. We demonstrate that fast Fourier-transform second-harmonic generation (FFT-SHG) technique provides an elegant solution to obtain polarization patterns of degrading structures. ispartof: Frontiers in optics ispartof: Frontiers in optics date:6 Oct - 10 Oct 2013 status: published