Abstract:The optical properties of nanoparticle clusters vary with the spatial arrangement of the constituent particles, but also the overall orientation of the cluster with respect to the incident light. This...
“…We will assume that the filter, composed of randomly oriented helices embedded in a homogeneous medium with the refractive index of either vacuum or water, can be treated as a single homogenized material. The power loss experienced by a circularly polarized beam propagating along this material in the forward direction can be expressed through the rotationally averaged helicity extinction cross sections for the respective polarization , of the helices, σ ext,± . If we consider a slab of this homogenized material with a thickness Δ z , assuming that it is thin enough for the power flux of the incident beam remaining approximately constant, the power per unit area absorbed or scattered by the medium with a helix number density ρ helices can be obtained aswith S z being the component of the time averaged Poynting vector along the propagation direction of the beam.…”
Designing objects
with predefined optical properties is a task
of fundamental importance for nanophotonics, and chirality is a prototypical
example of such a property, with applications ranging from photochemistry
to nonlinear photonics. A measure of electromagnetic chirality with
a well-defined upper bound has recently been proposed. Here, we optimize
the shape of silver helices at discrete frequencies ranging from the
far-infrared to the optical band. Gaussian process optimization, taking
into account also shape derivative information on the helices scattering
response, is used to maximize the electromagnetic chirality. We show
that the theoretical designs achieve more than 90% of the upper bound
of em-chirality for wavelenghts 3 μm or larger, while their
performance decreases toward the optical band. We fabricate and characterize
helices for operation at 800 nm and identify some of the imperfections
that affect the performance. Our work motivates further research both
on the theoretical and fabrication sides to unlock potential applications
of objects with large electromagnetic chirality at optical frequencies,
such as helicity filtering glasses. We show that, at 3 μm, a
thin slab of randomly oriented helices can absorb 99% of the light
of one helicity while absorbing only 10% of the opposite helicity.
“…We will assume that the filter, composed of randomly oriented helices embedded in a homogeneous medium with the refractive index of either vacuum or water, can be treated as a single homogenized material. The power loss experienced by a circularly polarized beam propagating along this material in the forward direction can be expressed through the rotationally averaged helicity extinction cross sections for the respective polarization , of the helices, σ ext,± . If we consider a slab of this homogenized material with a thickness Δ z , assuming that it is thin enough for the power flux of the incident beam remaining approximately constant, the power per unit area absorbed or scattered by the medium with a helix number density ρ helices can be obtained aswith S z being the component of the time averaged Poynting vector along the propagation direction of the beam.…”
Designing objects
with predefined optical properties is a task
of fundamental importance for nanophotonics, and chirality is a prototypical
example of such a property, with applications ranging from photochemistry
to nonlinear photonics. A measure of electromagnetic chirality with
a well-defined upper bound has recently been proposed. Here, we optimize
the shape of silver helices at discrete frequencies ranging from the
far-infrared to the optical band. Gaussian process optimization, taking
into account also shape derivative information on the helices scattering
response, is used to maximize the electromagnetic chirality. We show
that the theoretical designs achieve more than 90% of the upper bound
of em-chirality for wavelenghts 3 μm or larger, while their
performance decreases toward the optical band. We fabricate and characterize
helices for operation at 800 nm and identify some of the imperfections
that affect the performance. Our work motivates further research both
on the theoretical and fabrication sides to unlock potential applications
of objects with large electromagnetic chirality at optical frequencies,
such as helicity filtering glasses. We show that, at 3 μm, a
thin slab of randomly oriented helices can absorb 99% of the light
of one helicity while absorbing only 10% of the opposite helicity.
The correlation between the orientation of the two π-electron systems and the chiroptical properties was investigated using two types of optically active X-shaped molecules consisting of planar chiral [2.2]paracyclophanes. The X-shaped molecules exhibited high photoluminescence quantum efficiencies and good circularly polarized luminescence properties with relatively high anisotropy factors of the order of 10 À 3 . It was experimentally and theoretically elucidated that the chiroptical properties of the two molecules were almost identical, regardless of the orientation of the stacked π-electron systems.
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