This paper reports on the giant circular dichroic second-harmonic generation (CD-SHG) behavior of double SP resonant chiral Al nanorod (AlNR) dimer structures. The two AlNRs are aligned in a straight line. It becomes chiral, when one of the AlNRs is shifted laterally from it. We obtained CD-SHG signals up to 0.5 for the corresponding amount of the shift. Additionally, the sign of the CD-SHG was reversed, when the sign of the shift was reversed. The amount of the CD-SHG was flexibly tunable by changing the amount of the shift, which was the uniqueness of the present chiral plasmonic nanostructure.
The paper reports the second harmonic generation (SHG) behaviors of dolmen-type Au nanorod (AuNR) trimer structure, in which two of the AuNR’s are arrayed in parallel and the third is arrayed perpendicular to them. Our experimental results demonstrated that the SHG signal from the trimer was 25 times higher than that from the referential isolated AuNR monomer and dimer. The geometry of the AuNR was centro-symmetric, and it was forbidden in the second-order nonlinear susceptibility under the electric dipole approximations. The coupled plasmon mode in noncentrosymmetrically arranged trimer provided the nanometric optical fields suitable for the 2nd-order nonlinear optics.
Second harmonic generation (SHG) behaviors will be presented for NLO polymer/Au nanoparticle hybrid structures. The NLO polymer is the material rich in the nonlinear susceptibilities and it is suitable for coating on the metal surfaces. The Au nanoparticles themselves exhibit enhanced SHG effects at localized surface plasmon (LSP) resonances. Our experimental results demonstrated that the Au nanoparticles coated with the NLO polymer emitted more than one magnitude higher SHG signals than the bare Au nanoparticles. The enhanced nonlinearities due to the NLO polymers were explained in terms of not only electromagnetic mechanism but also molecule-to-metal charge transfer mechanism.
We present second harmonic generations (SHG) of NLO polymers grown on Ag thin films at surface plasmon polariton (SPP) resonances. The Ag film itself exhibits surface nonlinear susceptibility and it is enhanced at the SP resonances. Our experimental results demonstrated that growing the NLO polymer layers on the Ag films was useful for further amplifying the conversion efficiencies of the SP-enhanced SHG. There was optimal polymer thickness for the SHG conversions, and approximately 40-fold maximum amplification was gained. The dependency of the SHG conversions on the polymer thickness was explained in terms of the bulk nonlinearities and the multiple reflections inside the polymer layer.
The paper presents second harmonic generations (SHG) from Au nanoprisms at localized surface plasmon resonances.
The model system was equilateral triangular nanoprisms that were arranged two-dimensionally in trigonal lattices. At
lower excitation power regions, the SHG conversion efficiencies were almost independent of the excitation light
polarization angles, while the polarization angles of the SHG waves were twice as much as those of the excitation light
polarizations. The polarization dependencies were in a good agreement with the demands required from the C3v point
symmetry of the systems. On the other hand, the SHG conversion efficiencies were dependent on the excitation light
polarization angles at higher excitation power regions. The anisotropy in the nonlinear optical responses was explained
from the viewpoint of the polarization-dependent depletions of the surface electrons on the metal surfaces.
We present second-order nonlinear optical properties of two-dimensional periodic arrays of Au nanorods arranged two dimensionally on SiO2 along with the one-dimensional periodic arrays in the direction either coaxial or vertical to the plasmon polarizations. The geometry of the nanorods was symmetric with respect to the normal line to the top surface of the rods, and the system was excited at oblique incidence angles so as to break the centro-symmetry. Our experimental results demonstrated that the coordination longitudinal to plasmon polarizations reduced the nonlinearities of the nanorods while the coordination transverse to polarizations did not give any significant influences on them.
The second harmonic generations (SHG) from Au nanorods coated with the nonlinear optical (NLO) polymers will be presented. The thin films of the NLO polymers with the different transition frequencies were prepared. The SHG conversion efficiencies were highly enhanced by coating the NLO polymers on the nanorods. The conversion efficiencies were higher, as the transition wavelengths of the NLO polymers were closer either to the pump light wavelength or its second harmonic wavelength. About five-fold enhancement in the conversion efficiency was recorded from the nanorods of which absorption peak was almost exactly resonant to the second harmonic wavelength, comparing with that from the pristine PMMA coated nanorods.
The presentation will report nonelectrical poling behaviors of guest-host polymers, consisting of Disperse Red1 (DR1)
and poly (methyl methacrylate) and related second-order nonlinear optical susceptibilities. Our present experimental
results found the emissions of the second harmonic generations from the polymer thin films on SiO2 glass substrates after annealing the materials at the temperatures higher than the glass transition temperatures of the PMMA even in the absence of applying the external electric fields. The hydrogen bonds between the hydroxyl groups of the DR1 and the
silanols of the substrate surely played essential roles for breaking the centrosymmetry in the alignments of the guests.
The optimized conditions of the nonelectrical poling procedures were examined from the standpoints of the polymer film
thickness and the concentrations of the guest chromophores.
We will report second harmonics generations (SHG) in nonlinear optical (NLO) polymers excited by Surface Plasmon
(SP) enhanced fields. The surface plasmon polariton was excited in an attenuated total reflection geometry having the
Kretchmann configuration. Here, the NLO interactions occurred in the thin films of the NLO polymers, consisting of
Disperse Red 1 as guest chromophores and PMMA as host, coated on Ag thin films. Our experimental results indicated
that NLO polymers emitted strong SHG signals in the SP resonance conditions. The SHG intensities from NLO polymer
coated Ag films were more than 10 times higher than those of the uncoated Ag films. The measurements were conducted
for the polymer films with different thickness between 10 and 100 nm. All of the samples with different polymer
thickness exhibited the SHG signals at its SP resonance condition that depends on the film thicknesses. The highest SHG
conversion efficiency was recorded from the sample with 40 nm film thicknesses. The p-polarized pump beams gave the
highest SHG conversion efficiency while the s-polarized ones gave almost no signals. On the other hand, the
polarizations of the SH signals were highly oriented in the direction of the p-polarizations. The SP-enhanced field
attracts a lot of interests as light sources for sub-diffraction-limit imaging. The SP can be excited only in the regions
lower than surface plasma frequencies peculiar to the metals. The present frequency conversion technologies for the SP
enhanced fields in the NLO polymers will extend the frequency regions available for the sub-diffraction-limit imaging.
Here, we will propose poly (cyano phenylene sulfide) as novel host materials of nonlinear optical (NLO) polymers. Our
experimental results proved that NLO chromophore-doped PCPS thin films deposited on the metal layers exhibited
second order NLO susceptibilities just by annealing at the temperatures higher than a glass transition point even without
conventional poling procedures. We determined the optimized annealing temperatures and the film thickness for the
nonelectrical poling procedure. The nonelectrical poling procedure was applicable for the films as thick as a few μm.
The second order nonlinear coefficient of was 0.5 pm/V for the PCPS doped with 10w% of 4-[Ethyl(2-
hydroxyethyl)amino]-4'-nitroazobenzene. Taking advantage of the unique polarization self-organization procedure, we
may prepare one- or two-dimensionally periodically poled structures in these materials for the second-order NLO active
photonic crystals pretty easily.
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