Metallic nanobowtie is well known as a suitable structure for development of antennas that can be integrated on wide
number of devices, especially in optical communications. Such feature is achieved due the presence of surface plasmon
polariton (SPP) that provides a great charge density on nearby region from its tips. Considerable studies have described
theoretical and experimentally the influence of gap between tips on radiation emission, once this parameter may improve
the local field, as such length decrease. In optical regime, the emission enhancement is due the quantum-plasmonic
interaction created from tips’ region (localized field) and the transition levels from rare earth ion of erbium (Er3+) and
thulium (Tm3+). However, metallic nanobowtie with absence of gap still deserve attention, because in addition to present
similar properties from regular case as previously mentioned, can also interacts with different systems, like gain
materials, that can be embedded thermically into the substrate. Rare earth ion is one of the remarkable and suitable for
our proposition, not only for the enhancement on measured intensity, but also its easiness to implement it on glasses,
which constitute the main type of substrate adopted on plasmonic structures. In this work we performed the analysis of effects due implementation of Er3+ and Tm3+ ions into BK7 glass over a pattern of nanobowtie on absence of gap
between its tips, fabricated by focused ion beam (FIB) technique from gold (Au) films. The bowties were vertically
excited by an Argon laser (Ar) which wavelength ( ) is 488 nm. Furthermore, computational simulations based on finite
element method (FEM), were performed to verify the dependence of nanobowtie’s geometry over the electric field along its symmetry axis.
High crystalline quality erbium-doped zirconium oxide films were deposited on Si(100) by electron beam evaporation in high vacuum. Characteristics of light emission in the telecommunication window from erbium oxide crystal zirconium oxide films were investigated before and after furnace annealing in oxygen atmosphere. The luminescence intensity of the erbium-doped thin film after annealing at 900 °C was 18 times higher than those before thermal annealing. Also, it was observed a decrease in the intensity of luminescence and the 4I13/2 lifetime with the increase of the erbium concentration, which was analyzed via energy transfer - quenching. The structure environment of the erbium ion in the thin film before and after annealing has been studied by X-ray diffraction. The surface morphology of the films as a function of the annealing temperature and atmosphere showed a significant change.
Metallic nanostructures upon resonant excitation can enhance the local electric field, which could be increased, if these nanostructures are embedded in a gain medium. In this sense, we propose a gain medium as a candidate for the development of nanowaveguide amplifier based on Er3+-doped tellurite glass with embedded silver nanoparticles (NPs). Those glasses are characteristic for their amplifying response in the telecommunication window, and when we embedded metallic NPs modified the crystalline potential surrounding to the Er3+ ions, due to an electric coupling between NP (received/emitter) and Er3+ ion (emitter) enhancement luminescence intensity from the 4I13/2→4I15/2 transition radiative of the Er3+ ions. Besides, the presence these NPs changes the refraction index these glass modifying the complex parameter β(neff) increasing the polarizability of the samples f(Ɛd). Therefore, a gain medium – Er3+ ions (amplification function in the telecommunication band) with silver NPs (luminescence enhancement) – can increment the propagation length of light into nanowaveguide.
Currently, the focused ion beam milling (FIB) technique is a commonly used approach to fabricate nanostructures because of its unique advantages of one-step fabrication, nanoscale resolution, and no material selectivity, etc. However, the FIB technique also has its own disadvantages. Regarding the process of fabrication of the corrugations and subwavelength apertures, nowadays, there is a major problem: the V-shaped structuring. In this work, we discuss the influence of V-shape on the optical transmission of subwavelength slits designed in silver (Ag) and gold (Au) thin films possessing different thicknesses. The effect of different cone angles (ratio between the widths at the incidence plane and at the exit plane) originated from the V-shaped slits was also considered. We had performed computational simulations carried out with COMSOL Multiphysics® to investigate the slits optical transmission. In most cases, the subwavelength slits were illuminated with 488 nm (for Ag) and 632.8 nm (for Au) wavelength light sources in TM polarization (magnetic H-field component parallel to the axis of the slits). The origin of the slits transmission is attributed to plasmonic surface excitations. Our simulation results demonstrated that different cone angles originated from the Vshaped subwavelength slits generate different influences on the beam propagation. The width variation affects the optical transmission intensity significantly. Hopefully, exploring the influence on the light propagation behaviour through subwavelength apertures via theoretical simulations can provide a better understanding of the beam propagation phenomena for future studies.
A device consisting of a disk-shaped, Moiré-type plasmonic cavity placed inside a plasmonic crystal cavity, with a 250
nm polymethyl-methacrylate (PMMA) film over the cavities is analyzed by 3D finite-difference time domain (FDTD).
Both cavities can be fabricated by Focus Ion Beam, and the waveguide and the Moiré cavity contour can be defined by
one-step lithographic process. The device is characterized by calculating the cavity spectrum, the reflection and the
radiation spectra and the electric field intensity distribution. It was verified that the transverse-magnetic (TM) input
mode generates surface plasmon polaritons (SPP) at the PMMA/gold interface that excites localized surface plasmon
polariton on the Moiré cavity, that, in turn, generates reflected waves back to the waveguide and diffracted radiation.
Also, the lack of plasmonic crystal bandgap permits the evanescent coupling of Bloch waves to the plasmonic crystal.
The high electric field generated by the LSPP on the Moiré surface, and by the Bloch waves at the borders of the
plasmonic crystal holes, contributes to the fluorescence of molecules dissolved in the PMMA film. The radiated
fluorescence can be detected by a lensed fiber placed above the Moiré surface, and the reflected signal can be detected at
We report the 3D simulation of a disk-shaped, Moiré-type plasmonic cavity inside a photonic crystal cavity. The
simulation consider normal incidence of light over the sample to be analized with a confocal microscope in reflection
mode. The plasmonic cavity is made of gold, 250 nm of thickness, whose surface is modulated by a sinusoidal function.
The photonic crystal cavity is made in silicon nitride film (150 nm of thickness) over a SiO2 film (500 nm) on a silicon
substrate, the overall structure being Si/SiO2/SiN/Au. The simulation results show a three-fold enhancement of the
electric field intensity for the plasmonic cavity within the photonic cavity, in comparison with that for the plasmonic
cavity without the photonic crystal cavity. The result indicates that the electric field intensities of the photonic crystal
cavity modes add to the scattered field of the plasmonic cavity, thus enhancing the electric field just above the plasmonic
cavity. A preliminary test of the structure was done with a 300 nm gold film over a silicon substrate, made by focus ion
beam (FIB) milling, to show fluorescence enhancement of porphiryn molecules. The structure can be elaborated to serve
either as fluorescence enhancement of molecules or as Surface-enhancement Raman scattering (SERS) sensor.
Periodic nanostructure arrays forming electric dipoles or quadrupoles were fabricated with a Focused Gallium Ion Beam
on a gold thin film deposited onto an Er3+-doped tellurite glass. The nanostructures were vertically illuminated with an
Argon Ion laser (488 nm). The Er3+ luminescence spectrum was then measured in the far-field. The observed
luminescence is elucidated considering the following effects: (i) excitation of the Er3+ ions by means of the localized
surface plasmon resonance from the electric dipole/quadrupole nanostructures, that produce an improvement of the local
field, resulting in an enhanced luminescence, and (ii) the Er3+ luminescence spectrum depends on the albedo of the
system (electric dipole/quadrupole arrays), for which its resonant properties is strongly affected. In this way, the
emission of the Er3+ is achieved through the metallic nanostructures. Additional contributions for the observed emission
spectrum regarding the influence of physical and geometrical parameters, period of the electric multipole and lattice
symmetry have been investigated. The variation of these parameters resulted in a significantly improvement of
Plasmonic lenses consisting of convex/concave concentric rings with different periods were milled with a Focused
Gallium Ion Beam on a gold thin film deposited onto an Er3+-doped tellurite glass. The plasmonic lenses were vertically
illuminated with an Argon Ion laser (488 nm) highly focused by means of a 20x objective lens. The focusing mechanism
of the plasmonic lenses is explained by using a simple coherent interference model of surface plasmon-polariton
generation on the circular grating as a result of the incident field. Particularly, this beam focusing structure has a
modulated groove depth (concave/convex). As a result, phase modulation can be accomplished by the groove depth
profile, similarly to a nano-slit array with different thicknesses. This focusing allows a high confinement of SPPs which
excited the Er3+ ions of the substrate. The luminescence spectrum of Er3+ ions was then measured in the far-field, where
we could verify the excitation yield of the plasmonic lens on the Er3+ ions. We analyze the influence of physical and
geometrical parameters on the emission spectra, such as the periodicity and depth profile of the rings. The variation of
these parameters resulted in considerable changes of the luminescence spectra.
Multilayered Ag/Au/Ag/Au and Au/Ag/Au/Ag films with 200 nm of thickness (50 nm for each layer) were evaporated
onto BK7 glass substrates. Sequences of slits (around 60-600 nm of width) were milled with a focused gallium ion beam
in the films. We have undertaken a series of high-resolution measurements of the optical transmission through the slits.
The transmission measurement setup consists of 488.0 nm (for the Ag/Au/Ag/Au film) and 632.8 nm (for the
Au/Ag/Au/Ag sample) wavelength light beams from Ar ion and HeNe lasers, respectively, aligned to the optical axis of a
microscope. The beam is focused onto the sample surface by a microscope objective in TM polarization (magnetic Hfield
component parallel to the long axis of the slits). As well, theoretical estimates investigating the slits optical
transmission were performed. The origin of the slits transmission is mainly attributed to plasmonic surface excitations.
Based on the present results, it was possible to observe that (1) the transmission increases linearly with increasing slit
width, and (2) the transmission of the multilayered structures is augmented in comparison with a single perforated metal
film of equal thickness, for a fixed slit width. A very good correspondence between theory and experiment was observed.