An official website of the United States government
Plasmonic nanoparticles with chiral resonances in the visible wavelengths complement optical dissymmetry in the ultraviolet and near-infrared wavelengths in natural products and metamaterials respectively. Here, we show that under oxidative conditions, hot holes photogenerated with circularly polarized light in gold nanoprisms can spatially direct the photodeposition of lead oxide (PbO2), resulting in chiral nanostructures tunable with the polarization and wavelength of light. We observe a g-factor of 3.6 × 10–3, which can be attributed to the enhanced optical dissymmetry with PbO2 deposition of the side of nanoprisms upon illumination with green 532 nm light. Our finite-difference time-domain calculations support the site-specific photodeposition of PbO2 onto nanoprisms. This work shows that plasmonic nanoparticles can have tunable chiral properties imbued as a function of the wavelength and polarization of light.
more »
« less
Stokes Spectropolarimetry Applied to Measure Circular Birefringence Dispersion of Aqueous Solutions of Sugars
ABSTRACT Circular birefringence (CB) is defined as the difference in refractive index for opposite circular polarization states and has played a crucial role in the development of stereochemistry and the concept of chirality. It manifests experimentally as optical rotatory dispersion (ORD), that is, the wavelength‐dependent optical rotation of the plane of light polarization. However, most methods for probing ORD rely on analyzing transmitted light asymmetry at single wavelengths (usually the sodium D‐line at 589 nm) with linear polarizers, which cannot discern between unpolarized and circularly polarized light, limiting the apparatus to analyze a single phenomenon. Here we showcase the use of Stokes spectropolarimetry (SSP), a versatile and cost‐effective technique, to probe ORD of circularly birefringent materials. This technique allows complete analysis of the dispersive changes in polarization caused by anisotropic media, portraying a versatile experimental framework to study different types of optical anisotropies with a single spectropolarimeter. Here, aqueous solutions of chiral sucrose, fructose, and their mixtures are investigated. The ORD acquired verify that the optical rotation is proportional to the concentration of the chiral species and follows an inverse proportion with wavelength. As a case study, we show via SSP that ORD at 589 nm (D‐line of sodium) is in good agreement with literature (+63.5° ± 1.4° mL g−1 dm−1for sucrose and −83.7° ± 2.0° mL g−1 dm−1for fructose).
more »
« less
- Award ID(s):
- 1848418
- PAR ID:
- 10614104
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chirality
- Volume:
- 37
- Issue:
- 7
- ISSN:
- 0899-0042
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Optical phase-change materials exhibit tunable permittivity and switching properties during phase transition, which offers the possibility of dynamic control of optical devices. Here, a wavelength-tunable infrared chiral metasurface integrated with phase-change material GST-225 is demonstrated with the designed unit cell of parallelogram-shaped resonator. By varying the baking time at a temperature above the phase transition temperature of GST-225, the resonance wavelength of the chiral metasurface is tuned in the wavelength range of 2.33 µm to 2.58 µm, while the circular dichroism in absorption is maintained around 0.44. The chiroptical response of the designed metasurface is revealed by analyzing the electromagnetic field and displacement current distributions under left- and right-handed circularly polarized (LCP and RCP) light illumination. Moreover, the photothermal effect is simulated to investigate the large temperature difference in the chiral metasurface under LCP and RCP illumination, which allows for the possibility of circular polarization-controlled phase transition. The presented chiral metasurfaces with phase-change materials offer the potential to facilitate promising applications in the infrared regime, such as chiral thermal switching, infrared imaging, and tunable chiral photonics.more » « less
-
Abstract All‐optical control and detection of magnetic states for high‐density recording necessitate nanophotonic approaches to amplify local light intensity below the diffraction limit. Sculpting the near‐field phase and polarization can additionally strengthen magneto‐optical effects that rely on circularly polarized pulses, such as all‐optical helicity‐dependent switching, imaging, and spin‐wave excitation. Here, high‐refractive‐index dielectric nanoantennas illuminated with circularly polarized light resonantly enhance local electric field rotation by more than sixfold within [Pt/Co]Nthin films. Sub‐wavelength arrays of amorphous Si nanodisks, or metasurfaces, patterned on perpendicularly magnetized films support Mie‐type resonances that modulate reflection and transmission dissymmetry by >±2% in experiments. Spatial and spectral interference between dipolar modes, proximity effects, and gain are evaluated by varying disk aspect ratio, metasurface–metal separation, and magnetic film thickness, respectively. Simulated enhancements in magnetic circular birefringence and differential absorption are correlated with amplified local field rotation at electric dipolar modes. Greater achievable amplifications are shown via simulations with single‐crystalline Si metasurfaces exhibiting lower losses, including a 12‐fold strengthened electric field rotation within ferromagnetic layers. The metasurface design rules established here could enable nanoscale localization of all‐optical magnetic switching with lowered laser fluence thresholds, as well as enhanced magneto‐optical responses for light‐assisted reading in spintronic devices.more » « less
-
Creating artificial matter with controllable chirality in a simple and scalable manner brings new opportunities to diverse areas. Here we show two such methods based on controlled vacuum filtration - twist stacking and mechanical rotation - for fabricating wafer-scale chiral architectures of ordered carbon nanotubes (CNTs) with tunable and large circular dichroism (CD). By controlling the stacking angle and handedness in the twist-stacking approach, we maximize the CD response and achieve a high deep-ultraviolet ellipticity of 40 ± 1 mdeg nm−1. Our theoretical simulations using the transfer matrix method reproduce the experimentally observed CD spectra and further predict that an optimized film of twist-stacked CNTs can exhibit an ellipticity as high as 150 mdeg nm−1, corresponding to agfactor of 0.22. Furthermore, the mechanical rotation method not only accelerates the fabrication of twisted structures but also produces both chiralities simultaneously in a single sample, in a single run, and in a controllable manner. The created wafer-scale objects represent an alternative type of synthetic chiral matter consisting of ordered quantum wires whose macroscopic properties are governed by nanoscopic electronic signatures and can be used to explore chiral phenomena and develop chiral photonic and optoelectronic devices.more » « less
-
Chiral plasmonic surfaces with 3D “forests” from nanohelicoids should provide strong optical rotation due to alignment of helical axis with propagation vector of photons. However, such three-dimensional nanostructures also demand multi-step nanofabrication, which is incompatible with many substrates. Large-scale photonic patterns on polymeric and flexible substrates remain unattainable. Here, we demonstrate the substrate-tolerant direct-write printing and patterning of silver nanohelicoids with out-of-plane 3D orientation using circularly polarized light. Centimeter-scale chiral plasmonic surfaces can be produced within minutes using inexpensive medium-power lasers. The growth of nanohelicoids is driven by the symmetry-broken site-selective deposition and self-assembly of the silver nanoparticles (NPs). The ellipticity and wavelength of the incident photons control the local handedness and size of the printed nanohelicoids, which enables on-the-fly modulation of nanohelicoid chirality during direct writing and simple pathways to complex multifunctional metasurfaces. Processing simplicity, high polarization rotation, and fine spatial resolution of the light-driven printing of stand-up helicoids provide a rapid pathway to chiral plasmonic surfaces, accelerating the development of chiral photonics for health and information technologies.more » « less
