Tuning dipolar and multipolar resonances of chiral silicon nanostructures for control of near field superchirality

Chiral materials display a property called optical activity, which is the capability to interact differentially with left and right circularly polarised light. This leads to the ability to manipulate the polarisation state of light, which has a broad range of applications spanning from energy efficient displays to quantum technologies. Both synthesised and engineered chiral nanomaterials are exploited in such devices. The design strategy for optimising the optical activity of a chiral material is typically based on maximising a single parameter, the electric dipole–magnetic dipole response. Here we demonstrate an alternative approach of controlling optical activity by manipulating both the dipole and multipolar response of a nanomaterial. This provides an additional parameter for material design, affording greater flexibility. The exemplar systems used to illustrate the strategy are nanofabricated chiral silicon structures. The multipolar response of the structures, and hence their optical activity, can be controlled simply by varying their height. This phenomenon allows optical activity and the creation of so called superchiral fields, with enhanced asymmetries, to be controlled over a broader wavelength range, than is achievable with just the electric dipole–magnetic dipole response. This work adds to the material design toolbox providing a route to novel nanomaterials for optoelectronics and sensing applications

High-throughput SRCD using multi-well plates and its applications

The sample compartment for high-throughput synchrotron radiation circular dichroism (HT-SRCD) has been developed to satisfy an increased demand of protein characterisation in terms of folding and binding interaction properties not only in the traditional field of structural biology but also in the growing research area of material science with the potential to save time by 80%. As the understanding of protein behaviour in different solvent environments has increased dramatically the development of novel functions such as recombinant proteins modified to have different functions from harvesting solar energy to metabolonics for cleaning heavy and metal and organic molecule pollutions, there is a need to characterise speedily these system

Optical activity in Ge₂Sb₂Te₅ (GST)

Ge2Sb2Te5 (GST) is an established phase-change material that undergoes fast reversible transitions between amorphous and crystalline states with a high electro-optical contrast, enabling applications in non-volatile optical and electronic memories and optically-switchable structured metamaterials. We have recently demonstrated that optical activity can be induced in pure and doped GST thin films using polarised light, opening up the possibility of controlled induction of anisotropic phase transition in these and related materials for optoelectronic and photonic applications. While the phase transition has generally been understood to proceed via a thermal mechanism, our work strongly suggests that there is an electronic component of crystallization induced by the handedness of circularly polarised nanosecond laser pulses. Significant optical activity in the inorganic thin films, measured by circular dichroism spectroscopy at a synchrotron beamline, implies the existence of chiral structures or motifs. Optically active and inactive regions in the film have been studied using electron diffraction and spectroscopic techniques in order to obtain a structural picture that can be correlated to the optical changes observed. We also propose several mechanisms for the observed effects, which may be extended to other material systems and harnessed in photonic or chiroptical applications

Structural Characterization of Artificial Self-Assembling Porphyrins That Mimic the Natural Chlorosomal Bacteriochlorophylls c , d , and e

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