arXiv subjects

Shun Hashiyada

Publications and source records attributed to Shun Hashiyada.

6 recordsLinked to original sources

arXiv2026

Structured Optical Fields Reveal Nanoscale Chiral Light-Matter Interactions Governed by Optical Chirality

Optical chirality has been proposed as the local electromagnetic quantity governing chiral light-matter interactions, yet in conventional circularly polarized fields its magnitude is locked to the electric energy density, obscuring its independent role. Here we create a structured optical field in which optical chirality arises spatially in magnitude and sign while the electric energy density remains nearly uniform. A single chiral nanoparticle exhibits a differential response that follows this spatial variation, whereas no modulation is observed for an achiral nanoparticle, providing direct experimental evidence that optical chirality governs nanoscale chiral light-matter interactions. Measurements of wavelength-dependent optical rotation further provide an experimental estimate of the chiral polarizability, predicting a chiral gradient force of approximately 100 fN and a one-dimensional trapping potential exceeding the thermal energy at room temperature under optimized aqueous trapping conditions.

physics.optics↗

arXiv2026

Direct observation of anisotropic surface phonon polaritons on \alpha-quartz

Anisotropic surface phonon polaritons (SPhPs) offer extremely strong light confinement and unique light propagation characteristics, particularly on anisotropic polar crystals. Despite the classical importance of \alpha -quartz as a prototypical uniaxial bulk crystal, real-space observation of anisotropic SPhP propagation on \alpha-quartz has remained elusive. In this study, we report the first direct observation of SPhP propagating on an \alpha-quartz surface using scattering-type near-field optical microscopy (s-SNOM). We demonstrate that the dispersion relation and propagation length of SPhPs exhibit remarkable anisotropy depending on the propagation direction relative to the optic axis of \alpha-quartz. Furthermore, we verify that these experimental behaviors agree with theoretical calculations based on the dielectric permittivity tensors. Our results establish \alpha-quartz as a robust, highly promising platform for light-controlling nanodevices and mid-infrared on-chip sensing.

physics.optics↗

arXiv2025

Unveiling orbital optical chirality through multipolar chiral light-matter interaction

Chiral light-matter interactions have traditionally been understood in terms of electric-magnetic dipolar interference driven by light with spin angular momentum. Here, we show that optical chirality can also originate from the orbital angular momentum (OAM) of light, giving rise to higher-order multipolar chiral responses. Using a twisted gold nanorod dimer and tightly focused circularly polarized optical vortex beams carrying spin and orbital angular momenta of the same sign, we measure spectrally and spatially resolved chiral dichroism signals that persist even where spin optical chirality vanishes, revealing a quadrupole-mediated chiral interaction driven by OAM. The spectra reveal clear quadrupole resonances whose spectral profile is strongly modulated by the OAM sign, demonstrating an OAM-driven chiral interaction. Crucially, the signal satisfies optical reciprocity, ruling out artefacts from anisotropy or misalignment and confirming its nature as a true chiral response. Angular momentum dissipation analysis further shows that orbital contributions dominate over spin. These findings establish the existence of a distinct form of optical chirality, referred to as orbital optical chirality, which opens new avenues for probing and controlling multipolar chiral light-matter interactions beyond the dipolar paradigm.

physics.optics↗

arXiv2024

Conservation law for angular momentum based on optical field derivatives: Analysis of optical spin-orbit conversion

We present a theoretical framework for analyzing the loss of optical angular momentum (AM), including spin (SAM) and orbital (OAM) components, in light-matter interactions. Conventional SAM and OAM conservation laws rely on transverse field components, neglecting longitudinal fields and limiting applicability to vacuum. Our approach defines optical AM using time derivatives of the electric and magnetic fields, yielding a gauge-invariant formulation that includes both transverse and longitudinal components and explicitly incorporates charge and current densities. This enables a more complete description of AM dissipation in materials. We apply this framework to analyze spin-orbit conversion (SOC) in two scenarios: scattering of circularly polarized (CP) beams by a gold nanoparticle and focusing of CP and linearly polarized optical vortex beams by a lens. The results show that SOC depends on particle size and polarization, with notable OAM loss in larger particles and CP beam focusing. This framework enables the evaluation of previously overlooked SAM and OAM losses, providing a powerful tool for studying systems in which the analysis of AM losses is intrinsically important, such as chiral materials, as well as for designing photonic devices and exploring light-matter interactions at the nanoscale.

physics.optics↗

arXiv2023

Symmetry control of strong chiral light matter interactions in photonic nanocavities for efficient circularly polarised emission

Chiral excited electronic states of molecules have an intrinsic sense of handedness, or twist, and are the active component in energy efficient display technologies and in new photosynthetic routes to produce pharmaceuticals. Creating chiral states is achieved by manipulating the twistiness of the geometric molecular structure. This is a demanding problem adding complexity due to the need to precisely control molecular geometry. Here we demonstrate a novel concept for creating chiral excited states which does not rely on molecular structure. Instead, it depends on hybridising a non chiral molecule with a chiral electromagnetic field, producing a hybrid light matter chiral polariton state. This is achieved by a symmetry controlled strong chiral-light matter interaction between an electromagnetic mode of a chiral nanocavity and an achiral molecule, a concept referred to as the electromagnetic enantiomer. This electromagnetic mechanism simplifies the creation of chiral electronic states since it is far less demanding in terms of materials design. We have illustrated the concept using an exemplar system relevant to organic optoelectronic technology, producing efficient circularly polarised emission from a non-chiral emitter molecule.

physics.optics↗

arXiv2022

Near-field Probing of Optical Superchirality for Enhanced Bio-detection

Nanophotonic platforms in theory uniquely enable < femtomoles of chiral biological and pharmaceutical molecules to be detected, through the highly localised changes in the chiral asymmetries of the near-fields that they induce. However, current chiral nanophotonic based strategies are intrinsically limited because they rely on far-field optical measurements that are sensitive to a much larger near-field volume, than that influenced by the chiral molecules. Consequently, they depend on detecting small changes in far-field optical response restricting detection sensitivities. Here we exploit an intriguing phenomenon, plasmonic circularly polarised luminescence (PCPL), which is an incisive local probe of near-field chirality. This allows chiral detection of monolayer quantities of a de novo designed peptide, which is not achieved with a far-field response. Our work demonstrates that by leveraging the capabilities of nanophotonic platforms with the near-field sensitivity of PCPL, optimal biomolecular detection performance can be achieved, opening new avenues for nanometrology.

physics.optics↗