Advent of torsional optomechanics from Beth’s legacy

Torsional optomechanics,which involves the transfer of angular mo-mentum from light to matter,has been a vibrant research area since Beth’s pioneering contribution in 1935.Beth proposed a method to measure the transfer of spin angular momentum using a torsional pen-dulum,1 laying the foundation for classical and quantum optomechanics related to particle levitation,trapping,and cooling in modern optics.

Electromagnetic chirality:from fundamentals to nontraditional chiroptical phenomena

Chirality arises universally across many different fields.Recent advancements in artificial nanomaterials have demonstrated chiroptical responses that far exceed those found in natural materials.Chiroptical phenomena are complicated processes that involve transitions between states with opposite parities,and solid interpretations of these observations are yet to be clearly provided.In this review,we present a comprehensive overview of the theoretical aspects of chirality in light,nanostructures,and nanosystems and their chiroptical interactions.Descriptions of observed chiroptical phenomena based on these fundamentals are intensively discussed.We start with the strong intrinsic and extrinsic chirality in plasmonic nanoparticle systems,followed by enantioselective sensing and optical manipulation,and then conclude with orbital angular momentum-dependent responses.This review will be helpful for understanding the mechanisms behind chiroptical phenomena based on underlying chiral properties and useful for interpreting chiroptical systems for further studies.

Capillary-force-induced collapse lithography for controlled plasmonic nanogap structures

The capillary force effect is one of the most important fabrication parameters that must be considered at the micro/nanoscale because it is strong enough to deform micro/nanostructures.However,the deformation of micro/nanostructures due to such capillary forces(e.g.,stiction and collapse)has been regarded as an undesirable and uncontrollable obstacle to be avoided during fabrication.Here,we present a capillary-force-induced collapse lithography(CCL)technique,which exploits the capillary force to precisely control the collapse of micro/nanostructures.CCL uses electron-beam lithography,so nanopillars with various shapes can be fabricated by precisely controlling the capillary-force-dominant cohesion process and the nanopillar-geometry-dominant collapse process by adjusting the fabrication parameters such as the development time,electron dose,and shape of the nanopillars.CCL aims to achieve sub-10-nm plasmonic nanogap structures that promote extremely strong focusing of light.CCL is a simple and straightforward method to realize such nanogap structures that are needed for further research such as on plasmonic nanosensors.

Elucidating the photoluminescence-enhancement mechanism in a push-pull conjugated polymer induced by hot-electron injection from gold nanoparticles

Understanding the photophysical interactions between the components in organic-inorganic nanocomposites is a key factor for their efficient application in optoelectronic devices. In particular, the photophysical study of nanocomposites based on organic conjugated polymers is rare. We investigated the effect of surface plasmon resonance(SPR) of gold nanoparticles(Au NPs) on the photoluminescence(PL) property of a push-pull conjugated polymer(PBDB-T). We prepared the hybrid system by incorporating poly(3-hexylthiophene)-stabilized Au NPs(P3 HT-Au NPs) into PBDB-T. The enhanced and blueshifted PL was observed in the hybrid system compared to PL in a neat PBDB-T system, indicating that the P3 HT chains attached to the Au NPs suppressed charge-transfer from PBDB-T to the Au NPs and relayed the hot electrons to PBDB-T(the band-filling effect).This photophysical phenomenon limited the auto-dissociation of PBDB-T excitons. Thus, the radiative recombination of the excitons occurred more in our hybrid system than in the neat system.