The nonlinear absorption properties of Ag nanoprism arrays synthesized by nanosphere lithography have been investigated by z-scan measurements. A picoseconds and low repetition rate laser source has been used to excite the electronic component of the nonlinear optical response without inducing thermal effects on the samples. Spectral effects in the nonlinear absorption response have been highlighted by performing measurements at different wavelengths, matching the laser wavelength with the dipolar and the quadrupolar surface plasmon resonances of the synthesized nanoarrays. The nonlinear absorption properties of the samples have been also investigated as a function of the polarization of the laser source and dichroism effects have been revealed.
In this paper we report the linear and non-linear optical properties of metallic nano-clusters in α-Al2O3 fabricated by ion
implantation (from 2 to 8×1016 ions/cm2). Thereafter, the samples were annealed at temperatures from 600 to 1100 °C in
oxidising, reducing atmospheres. Once spherical nano-particles were synthesized, the samples were further irradiated
with Si+++ with different energies and fluences to control the achieved anisotropy. As a result of the ion implantation
mostly F+ color centers were formed. After thermal annealing they capture an electron to form F centers or combine to
form a F2+ center. Also, the photoluminescence signal from Al+ interstitials appears. Regarding the non-linear optical
response, the spherical-like Au nano-crystals embedded in sapphire show a positive non-linear absorption at 355 nm and
negative non-linear absorption at 532 nm, which shows saturation when increasing the incident irradiance. They also
present positive non-linear refraction at 532 nm, which is null at 355 nm. For the anisotropic systems, a larger
birefringence than natural values was measured in the visible range by ellipsometry means.
We present a nonlinear optical study using standard Z-scan technique at the picosecond regime, in a nanostructured
material containing both quasi-spherical silver nanoparticles and silicon quantum dots, and comparing its response to
those from similar systems, one with only silicon quantum dots, and another with only silver nanoparticles. The study
was done using different wavelengths, 355 nm and 532 nm, which are localized at both sides of the surface plasmon
resonance of the Ag nanoparticles, and 1064 nm, which is localized well far away of it. In general, we have observed that
the larger optical nonlinear response came from the sample with silver NPs. However, the combined system showed a
positive nonlinear refraction below the plasmon resonance (355 nm), changing to a negative value for wavelengths above
resonance (532 nm and 1064 nm). We observed also, for the combined system and for the three wavelengths used, a
saturation of the nonlinear refraction index as a function of the incident irradiance.
Gold nanoparticles (AuNPs) have proven to be powerful tools in various ultrafast photonic, plasmonic and nanomedical
applications. Numerous advances in the use of AuNPs include research on their interesting and remarkably fast changes
influenced by Surface Plasmon Resonance excitations. Within this work we report theoretical and experimental results
for the physical mechanisms that originate a nonlinearity of refractive index during different temporal regimes for a
high-purity silica matrix containing Au nanoparticles. The nanocomposites were prepared by ion implantation into a
silica matrix, followed by a thermal annealing. We used an optical Kerr gate with 80 fs pulses at 830 nm and a vectorial
self-diffraction technique with 26 ps and with 7 ns at 532 nm in order to investigate the magnitude and response time of
the resulting third order nonlinearity. In all cases we were able to measure and identify an electronic polarization
responsible for the nonlinear refraction. For the pico- and nano-second near resonance irradiations, a contribution of a
thermal effect could be stimulated and then the optical Kerr response enhanced. The presence of saturable absorption for
the pico- and nano-second experiments was measured. We observe that our samples behave like waveguides in the near
infrared spectrum and we estimate that they posses potential applications for all-optical switching devices.
Plasmonics is the most promising field appointed to continue the predictions of the Law of Moore as well as for the
confinement of light on a subwavelength spatial scale, allowing the breaking of the diffraction limit. In that direction, we
have produced by ion implantation, interesting nanocomposites with very attractive optical properties. Recently, a double
implantation of Si and Ag ions in silica, with subsequent thermal treatments in appropriated atmospheres, allowed us to
obtain two layers: one of Si nanocristals (NCs), and other of Ag nanoparticles (NPs). This arrangement shows an
enhancement of the emission of Si nanocrystals (NCs) in a new, totally integrated configuration. The synthesis of the
system by ion implantation offers a total protection of the optical active agents from environmental effects such as
oxidation, additionally assuring a high degree of homogeneity.
We present a photoluminescence excitation study (420-500 nm) of Si NCs, with and without the presence of Ag
nanoparticles (NPs), both embedded in a matrix of SiO2. The level of saturation for Si NCs is independent of the
excitation wavelength, but for Si NCs in the presence of Ag NPs, a saturation level arises for excitation wavelengths near
the absorption band of the surface plasmon resonance of the Ag NP (325-475 nm). The increase of both, the values of
saturation and excitation cross-section of Si NCs in the presence of Ag NPs, is an evidence of the optical interaction
between the metal NPs and Si NCs studied in this work. This suggests a decrease of the lifetime of Si NCs
photoemission due to the interaction with the Ag NPs.
A large effort has been devoted to the preparation of organic polymeric materials for electro-optic modulation and more recently for cascading based processes. These materials contain push-pull chromophores either incorporated as guest in a high Tg polymeric matrix (doped polymers) or grafted onto the polymeric matrix. These systems present several advantages but require significant improvement at the molecular level- by designing optimized chromophores with very large molecular figure of merit specific to each application targeted. The sol-gel route was used to prepare hybrid organic-inorganic materials, for the fabrication of amorphous solids of various shapes (bulk, think films...). The results obtained on optimized chromophore-doped poled thin films emphasize that intermolecular interactions have to be taken into account, as already pointed out by Dalton and coworkers. By combining a molecular engineering strategy for getting large molecular figure of merit and by controlling the intermolecular dipole-dipole interactions via both tuning the push-pull chromophore concentration and the incorporation screening carbazole moieties in high concentration. This strategy allows us to obtain a r33 of about 50 pm/V at 831 nm for a new optimized chromophore structure. In parallel, these thin films are being processed to be used as passive components for integrated optics.
We have developed hybrid organic-inorganic materials based upon the incorporation of nonlinear chromophores in a rigid amorphous inorganic matrix. Functionalized thin films have been prepared using the sol-gel route allowing for mild synthesis conditions. Push-pull chromophores were either incorporated as guests or grafted on a silica based backbone via a spacer. Orientation of the dipolar chromophores within the materials was performed using the Corona technique. By playing on the structure of the push-pull chromophores and on its orientational stability inside the matrix, functionalized materials with large electro-optic coefficients and excellent stability have been designed. By combining both appropriate push-pull chromophores and photoconductors grafted on the matrix, materials showing interesting photorefractive properties can be obtained without requiring the application of an external electric field. Both the presence of a strong internal field in the poled materials and the occurrence of photo-assisted orientational birefringence plays a significant role.
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