We demonstrate an efficient ENZ response in the visible spectral range using organic
molecular ultrathin films possessing a Lorentz-type dispersion. For this purpose, two
polymethine dyes: sodium [5,6-dichloro-2-[[5,6-dichloro-1-ethyl-3-(4-sulphobutyl)-
benzimidazol-2-ylidene]-propenyl]-1-ethyl-3-(4-sulphobutyl)-benzimidazolium hydroxide]
(TDBC), and [2,4-bis[8-hydroxy-1,1,7,7-tetramethyljulolidin-9-yl]squaraine]
(HTJSq) were used in spin-coated polymer films at different doping concentrations.
By varying the doping concentration in thin films, the real part of highly dispersive permittivity
ε1 can be manipulated and tuned such that the spectral width of ENZ region -1 < ε1 <1 resides
in the visible spectral range. These results are not only extremely relevant for applications
requiring a custom-tailored ENZ region in the visible but also provide important novel
information on how molecular aggregation affects the ENZ properties. In particular, based on our findings, we stress that J-aggregate is not always a mandatory molecular assembly for
obtaining a strong ENZ response. Instead, molecular aggregates with the size of a few
nanometers resulting in strong molecular interactions (i.e. Davydov splitting of the lowest
transition in energy) are required to achieve a strong ENZ response. The ENZ-enhanced optical
Kerr nonlinearity is then investigated in the optimum concentration films of TDBC and HTJSq.
Both nonlinear refractive index and nonlinear absorption coefficient are found to be strongly
enhanced in the ENZ region originating from the coupling of excitonic transition dipoles
associated with large molecular aggregates.
KEYWORDS: Silicon, Molecules, Near field scanning optical microscopy, Nanoantennas, Solid state physics, Antennas, Luminescence, Near field optics, Optical resonators, Resonators
Broadband subwavelength optical resonators have the ability to enhance the spontaneous emission rate and brightness of solid-state emitters. Recently, high-index dielectrics have been proposed as an alternative to plasmonic materials to design optical resonators with low ohmic losses. In this study, the interaction between a silicon nanoantenna and solid-state emitters is characterized by tuning the position of a 100 nm diameter fluorescent sphere in the vicinity of an e-beam fabricated silicon disk using scanning-probe microscopy. If the nanodisk resonance matches the emission wavelength of the fluorescent molecules, we observe enhanced decay rates at short distances; while, for an out-of-resonance antenna, the fluorescence lifetime is locally increased. Furthermore, our experiments highlight the ability of silicon antennas to increase far-field collection efficiencies, in agreement with numerical simulations (D. Bouchet et al, Phys. Rev. Applied 6, 064016 (2016)).
The intensity of spontaneous emission from fluorescent dye molecules can be further enhanced, by more than two orders of magnitude, in the nanoscale gap between silicon nanodisks. This is evidenced at the single molecule level using fluorescence correlation spectroscopy with freely diffusing emitters (R. Regmi et al, Nano Lett. 16, 5143 (2016)).
These results demonstrate the potential of silicon antennas for the manipulation of solid-state emitters at the nanoscale and at room temperature.
We investigate conditions of excitation and properties of Plasmonic Surface Lattice Resonances (PSLR) over glass substrate-supported Au nanoparticle dimers (~100-200 nm) arranged in a periodic metamaterial lattice, in Attenuated Total Reflection (ATR) optical excitation geometry, and assess their sensitivities to variations of refractive index (RI) of the adjacent sample dielectric medium. We show that spectral sensitivity of PSLR to RI variations is determined by the lattice periodicity (~ 320 nm per RIU change in our case), while ultranarrow resonance lineshapes (down to a few nm full-widthat-half-maximum) provide very high figure-of-merit values evidencing the possibility of ultrasensitive biosensing measurements. Combining advantages of nanoscale architectures, including a strong concentration of electric field, the possibility of manipulation at the nanoscale etc, and high phase and spectral sensitivities, PSLRs promise a drastic advancement of current state-of-the-art plasmonic biosensing technology.
We designed and fabricated cyclic group symmetric metamaterials (CGSMs), anisotropic media showing an extrinsic optical orbital Hall effect. An exchange of angular momentum between spin and orbital angular momenta takes place in an optical beam propagating through anisotropic media such as plasmonic nanoantennas of concentric ring and tapered arc (TA) shape. In case of TA antenna an cross-polarized circular polarization scattered beam exhibits an extrinsic orbital Hall effect.
The CGSMs possess n-fold rotation symmetry and they are composed of plasmonic TA antennas. In case of circular polarization, the TA antennas effectively scatter incident light depending on the beam helicity. Both amplitude and phase gradients take place along the azimuthal direction for cross-polarized beams.
We used electron beam lithography to fabricate 30nm thick gold metamaterials patterned on borosilicate glass substrates. Six types of CGSMs with the symmetry order n from 1 to 6 were fabricated and measured. Each CSGM is composed of multiple TA antennas with the width varying from 45nm to 150nm organized in 8*n azimuthal segments of concentric rings repeated with 600nm radial spacing.
Measurements of orbital Hall transverse shifts of circularly polarized beams of right/left helicity were carried out at a wavelength of 1300nm. Because TA antennas are arranged in a metamaterial with a cyclic group n-fold rotation symmetry, the extrinsic orbital Hall transverse shifts from CGSM exhibit a geometrical pattern with the same symmetry. However, CGSMs with odd and even symmetry orders show a strongly contrasting difference in the character of transverse shifts. The observed geometrical patterns agree well with those obtained from FDTD theoretical simulation.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.