We report our latest results on second harmonic generation (SHG) microscopy from arrays of G-shaped
chiral gold nanostructures. The nanostructures are arranged in unit cells composed of four Gs, each rotated
at 90° with respect to its neighbors. As it has already been demonstrated, for linearly polarized light, these
unit cells yield a pattern of four SHG hotspots. However, upon increasing the pitch of the nanostructured
arrays, extra hotspots can be observed at the edges of the unit cells. While the origin of these extra hotspots
remains to be elucidated, their position indicates a relationship to coupling behavior between the unit cells.
Scanning second harmonic generation (SHG) microscopy is becoming an important tool for characterizing
nanopatterned metal surfaces and mapping plasmonic local field enhancements. Here we study G-shaped
and mirror-G-shaped gold nanostructures and test the robustness of the experimental results versus the
direction of scanning, the numerical aperture of the objective, the magnification, and the size of the laser
spot on the sample. We find that none of these parameters has a significant influence on the experimental
results.
We present the results of numerical and experimental studies of spatial and temporal separation of femtosecond light
pulses in 1D photonic crystals (PC) in Laue diffraction geometry. The porous silicon PC are fabricated by
electrochemical etching using and contain 400 pairs of alternating layers with optical thickness 600 and 680 nm, so that
the center of the photonic band gap is placed at about 2600 nm. Spatial splitting of the laser pulse into two, one of them
corresponding to the transmitted beam and the second - to the diffracted one, are observed. It is shown that the diffraction
angle of the second beam changes when the wavelength of light is tuning, in accordance with the theoretical estimations.
We report that in the absence of electric dipole contributions, upon azimuthal sample rotation, the
corresponding SHG response was found to be chiral, i.e. it shows the presence of asymmetries with a sense
of rotation (lack of mirror symmetry). It was found that this sense of rotation reverses with the handedness
configuration (G and mirror-G, see Fig. 1). While it is apparent that the property originates in local field
enhancements of electric and/or magnetic multipoles, its explanation invites further theoretical research.
Optical properties of a planar array of composite Au/Co/Au magnetic plasmonic nanosandwiches of 60 and 110 nm in
diameter are studied using linear absorption and optical second harmonic generation (SHG) technique. Linear absorption
spectrum reveals a peak centered at about 2.1 eV, which is associated with the excitation of localized surface plasmon in
Au/Co/Au nanosandwiches. The nonlinear-optical experiments are performed using the fundamental radiation of YAG:
Nd3+ laser at 1064 nm, so that the SHG radiation corresponds to the resonant plasmon line. It is shown that in spite of
spatial inhomogeneity of such an ensemble, the SHG response in the nanosandwiches of the diameter 110 nm is
presumably polarized and specular, i.e. substantially coherent. At the same time, for nanosandwiches with the diameter
of 60 nm the SHG signal is observed in the form of the hyper-Rayleigh scattering. Plasmon-assisted effects in nonlinear-optical
response of nanosandwiches reveal themselves by different relative amplitude and phase of odd in magnetization
component of the SHG field as compared with those in plasmon-free continuous trilayer structure.
Optical second harmonic generation (SHG) in amorphous Si/SiO2 multiple quantum wells (MQW) is studied by means of SHG spectroscopy, SHG interferometric spectroscopy and X-ray double-axes reflectometry of the MQW samples with the Si quantum well thickness d ranging from 1.00 to 0.25 nm. The electron density profiles obtained from X-ray reflectometry data confirm multilayer structure presence and refine growth data on d values. The observed modification of the SHG spectra upon decreasing d is interpreted using combination of the resonant two-subband approximation for the nonlocal optical response of each quantum well with the generalized transfer-matrix formalism for the description of light propagation across the whole MQW structure. Agreement with the experiment shows that the description of the quadratic optical response of the MQW structure within the model of a nonlocal piecewise-continuous medium remains valid on the sub-nanometer scale.
We present the results of the experimental studies of nonlinear-optical and nonlinear magneto-optical properties of granular magnetic films exhibiting giant magnetoresistance effect. The samples under study are Co-containing nanogranular films of the composition (Co)x(Al2O3)1-x, the concentration of cobalt, x, being varied in a wide range. A strong azimuthal anisotropy in the intensity of the second (SHG) and third harmonics (THG) is observed which proves the anisotropic crystallographic structure of granular films. The nonlinear magneto-optical Kerr effect (NOMOKE) in SHG and THG is studied in the films for the geometry of the transversal magnetization. The dependence of the NOMOKE contrast in the SHG (THG) intensity is found to be a non-monotonous function of Co content in the films. The dependence of the magnetization-induced components of the quadratic susceptibility on the content of Co in the films is estimated.
Realization of enhancement of second-harmonic generation (SHG) in
three-dimensional (3D) photonic crystals utilizing nonlinear
diffraction is demonstrated. The samples are composed from
close-packed silicon oxide spheres with diameter of 250 to 300 nm in
each sample forming an ordered fcc opal matrix. The opal voids are
filled by noncentrosymmetric gallium nitride and centrosymmetric
silicon with filling factor close to unit. The photonic band gap
(PBG) is obtained for light reflected from the (111) face and
localized in the spectral region from 800 to 950 nm for different
samples. SHG spectra show pronounced peaks as the fundamental
radiation is tuned across the photonic band gap. The intensity
enhancement in SHG is about 100 and the spectral width of the SHG
resonances is approximately 15 nm. The SHG enhancement is attributed
to combination of linear diffraction of the fundamental radiation
from the (111) opal layers and nonlinear diffraction utilizing the
3D periodicity of the quadratic susceptibility of silicon and
gallium nitride nanocrystals in opal voids. The spectral position of
the SHG peak is slightly red-shifted in comparison with the PBG
center and attributed to condition of the group velocity minima.
The technique of fabrication of one-dimensional anisotropic photonic
crystals and microcavities based on porous silicon with
birefringence has been developed. The spectra of linear reflectance
demonstrate presence of photonic band gap (PBG) and microcavity mode
located in the center of PBG. Their spectral position is tuned upon
the sample rotation around its normal and/or rotation of incident
light polarization plane. Enhancement of second- and third-harmonic
generation for the fundamental wavelength resonant to the long
wavelength edge of PBG due to phase matching is observed by angular
spectroscopy. The angular positions of second- and third-harmonic
peaks are determined by porous silicon dispersion and shifted for
different polarisation of the fundamental wave due to the dielectric
function anisotropy.
This work is devoted to the first experimental observation of
optical features in spectra of reflectance and third-harmonic
generation of the finite one-dimensional photonic crystals based of
the porous silicon, which caused by "surface" modes of an
electromagnetic field, similarly to surface states of semiconductors
and dielectrics. Semiconductor surface states correspond to
electronic wave which total reflect from potential barrier
crystal-vacuum as well as crystal lattice due to Brag interference.
Therefore the electrons can propagate only along the crystal
surface. Similar effect can observed in electromagnetic spectrum of
photonic crystals. Although ordinary photonic crystals have not
potential barrier crystal-vacuum for photons but they have modified
density of modes at the surface. The surface waves existed at the
interface of two optically different media can be observed using
attenuated total reflectance configuration whereas the change of
density of modes gives a sensitive tool to observe optical
properties in the surface region. For observation optical features
associated to surface states of photonic crystal we have to create
the photonic crystal with few layers - finite photonic crystal. Also
we can observe changes of electromagnetic density of modes by using
third-harmonic generation spectroscopy. Dependence of resonances of
third-harmonic generation on number of layers in the structure was
observed. Increase of Q-factor of photonic crystals lead to wash out
optical features of surface modes in a linear spectrum, whereas the
nonlinear optics remains sensitive to eigenmodes.
We develop laser-based technologies for characterization and release of Surface Tension Energy (STE) in nanoparticle structures. Nanoparticle dispersed materials offer a very high potential to store energy in the form of Surface Tension. An important benefit of these systems is the increased safety and control of energy storage compared to existing chemical systems. The release technology is based on excitation of resonant plasmons in metal nanoparticles and their further laser-induced coalescence, whereas the characterization technology is related to the extraordinary sensitivity of nonlinear optical effects in nanoparticles to their surface conditions and properties. The direct relation between STE and nonlinear optical parameters of nanoparticles permits use of optical second-harmonic generation (SHG) to measure STE. The SHG probe can be applied to characterize surface properties of a wide variety of nanoparticle materials, particularly active and smart materials. In terms of surface energy elease, we concentrate on nanoparticle-dispersed materials in the form of arrays of metal nanoparticles. External laser radiation is considered to trigger interparticle coalescence due to excitation of local plasmons that are specific electro-magnetic modes in metal nanoparticles. Local plasmon excitation, in turn, lead to surface energy release in the wake of fusion of excited nanoparticles.
We consider the possibilities of developing smart nano-structured coverings that allow one dynamically change their color in the reflected light by modify spectral position of their reflection coefficient. The suggested technology is based on the recent progresses in the field of photonics and the fabrication of silicon-compatible photonic band gap (PBG) materials, photonic crystals. It is suggested to compose the PBG structures of porous silicon and infiltrate them with active nano-compounds whose optical features can be changed by the application of the electric field, current or illumination. As a result, the controlled change of color of the composed structure can be achieved.
Nano-coatings with adjustable optical features is one of the revolutionary technologies of today. In this work, we investigate how hyperspectral imaging can detect adjustable nano-surfaces used, for example, for active camouflage. The distinct attributes of the nano-coating spectra are discussed. Fast algorithms of utilizing hyperspectral information for recognizing these attributes are suggested. The research applies to both recognizing the camouflaged objects and to building unrecognizable camouflage technology. In the context of tracking active camouflage, the identification of
characteristic spectral attributes is especially important. Active spectra can constantly change, therefore confusing traditional hyperspectral classification. In contrast, the identified general spectral attributes stay the same allowing for robust identification and reliable tracking of the camouflaged objects.
Surface-enhanced optical third-harmonic generation (THG)is observed in silver island films. The THG intensity from 2-D array of silver nanoparticles is enhanced by two orders of magnitude and the enhancement is attributed to the local field resonance at third-harmonic wavelength mediated by excitation of the local surface lasmons.
KEYWORDS: Luminescence, Near field scanning optical microscopy, Silicon, Optical microcavities, Spectroscopy, Near field, Photonic crystals, Near field optics, Silicon photonics, Argon ion lasers
Photoluminescence spectroscopy of porous silicon photonic crystal microcavities is studied by the far-field and near-field robes using the apertureless scanning near-field optical microscope. Narrow microcavity mode with the spectral width of 10nm in far-field spectra and broad photoluminescence peak with the spectral width of 50nm in near-field spectra of microcavity samples is observed. It has been studied some correlations between near-and far-field spectra of porous silicon structures.
Incoherent: diffuse and depolarized,component of the enhanced third harmonic generation (THG)intensity is associated with the third-order hyper-Rayleigh scattering (HRS)in 2-D random ensemble of silver nanoparticles. A comprehensive analysis of the linear and nonlinear light scattering in combination with the results of atomic force microscopy revealed the fractal nature of the silver island films.
Nonlinear optical properties of granular magnetoresistive films are studied by second harmonic generation (SHG) technique and nonlinear magneto-optical Kerr effect (NOMOKE). For different types of granular structures - magnetic nanoparticles in non-magnetic metallic (Co-Cu) or in a dielectric host material (CoFe-Al2O3), a
clear correlation between GMR and NOMOKE is observed, which manifests itself in the appearance of a local maximum in both the GMR and NOMOKE for the same concentration range of magnetic metal prior to the
percolation threshold. This correlation apparently occurs on the macroscopic level due to the similar influence of the nanogranules structure on surface magnetization of granules which determines NOMOKE, and spindependent conductivity of the films.
KEYWORDS: Luminescence, Near field optics, Near field scanning optical microscopy, Near field, Photonic crystals, Silicon, Optical microcavities, Spectroscopy, Scattering, Optical fibers
The spatial distribution of the local optical field in the photonic crystal (PC) microcavities (MC) formed from porous silicon and in MC doped by fluorescent dye is studied by apertureless scanning near-field optical microscope (SNOM). To increase fluorescence up to 100 times photonic crystals are doped by fluorescence dye Rhodamin 6G. Photoluminescence spectroscopy of porous silicon photonic crystal MC is studied by far-field and near-field probes. The spatial distribution of optical field at the cleaved edge of MC is observed in
near-field scattering and photoluminescence. The image of the spatial distribution of local optical field in near-field fluorescence at the wavelength of local optical maximum of fluorescence spectra shows the localization of radiation in MC layer.
Incoherent third-harmonic (TH) generation, or hyper-Rayleigh scattering (HRS) on TH was observed for the first time, to our knowledge, from silver island films (SIF). The interpretation of the experimental results is based on the correlation between optical properties and structural features of SIF.
In this paper, results of the first observation of magnetization-induced second-harmonic generation (SHG) in one-dimensional magneto-photonic microcavities are described. Both significant magnetization-induced rotation of second-harmonic wave polarization and magnetization-induced variations of the SHG intensity are detected at the fundamental wavelengths in the vicinity of microcavity mode.
Size effects in optical second harmonic generation (SHG) from Si(001)-SiO2 planar micro-cavity structures are studied for fundamental wavelengths from 700 nm to 850 nm. The observed dependence of SHG intensity on the thickness of oxide layer is explained, in part, by an optical Casimir nonlocality arising from interference of zero-point fluctuations in micro-cavity, which is distinguished from microscopic interface effects. Detailed theoretical analysis of the Casimir nonlocal contribution to the quadratic susceptibility using a diagrammatic technique is performed for visible and IR regions. The difference in the length scale of the Casimir contribution at 800 nm and 1064 nm fundamental wavelength is discussed.
In this paper, we survey our previous and recent results of magneto-induced effects in second harmonic generation (SHG) from magnetic nanostructures. The degree of such effects is governed by the fine structure parameter and subsequently small in low order susceptibilities, yet enhanced at higher orders. One mechanism responsible for the enhancement of magneto-induced contributions to the SHG intensity is related to optical interference in the far-field region of the second harmonic fields generated by nonmagnetic and magneto-induced nonlinear polarizations. An interference model is considered for resonant and nonresonant, centrosymmetric and noncentrosymmetric media and is used to interpret the magneto-induced SHG results of Co nanocrystals and Gd monolayers.
Solid state femtosecond lasers enable powerful new nonlinear optical spectroscopic characterization techniques for technologically relevant Column IV and III-V semiconductor interfaces and growth surfaces.
For the first time the method of the second harmonic generation was used to study the photo- and electrically induced nonlinear optical transformations in thin oriented films of purple membranes (PM). Variations of the film nonlinear susceptibility were investigated as the bacteriorhodopsin (bR) molecule underwent the cycle of photoinduced transformations for both dry electrically oriented films and bR molecules embedded into poly(vinyl alcohol) matrix. The electrically induced changes of the nonlinear optical properties were studied for the electrostatic field strength up to the values 4 (DOT) 104 V/cm. Nonlinear susceptibilities of oriented and nonoriented dried PM films are compared.
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.