Structuring of a medium on the wavelength and subwavelength scales significantly enriches its interaction with light leading to new optical effects. As a result, it fuels the interest in planar artificial structures like photonic crystals, metasurfaces and plasmonic crystals, which have found tremendous success in light manipulation and applications in sensing, routing, light localization, enhancement of the nonlinear effects. The deep insight into optical phenomena in artificial structures requires necessarily numerical simulations. For periodic structures such as photonic crystals and diffraction gratings, numerical methods like finite-difference time-domain method (FDTD) and rigorous coupled-wave analysis (RCWA) are widely used. These methods have definite drawbacks, as the FDTD requires large computer memory to store the field values in the nodes of a 3D mesh, and high computational effort for the time simulation; the RCWA demands extra labor for the accurate treatment of a grating made of metal or anisotropic materials. Because the optical effects in highly anisotropic metal-based artificial structures like hypercrystals are of practical interest, we have proposed hybrid finite-difference frequency-domain (FDFD) approach for the calculation of light diffraction in such periodic structures. The improvement is achieved by handling the direct values instead of Fourier series, which is the core of the RCWA. Using this approach, we predict the excitation of the Dyakonov plasmons in hypercrystal formed by trenches in hyperbolic metamaterials.
The effect of the quantum properties of light on nonlinear processes has been well studied theoretically. It has been shown that the efficiency of n-photon nonlinear processes in many cases scales as the normalized n-th order correlation function. For light with high intensity correlation function, the efficiency of the n-th harmonic generation will be considerably higher than for coherent light. The experimental observation of this effect remained difficult until recently, because of the absence of bright sources with strong and fast intensity fluctuations.
For the experimental demonstration of statistical effects in optical harmonic generation we use as a pump the radiation of high-gain parametric down conversion. Such light shows quantum properties (e.g. quadrature or two-mode squeezing) and has large number of photons in one mode. The normalized n-th order correlation function for this light is (2n - 1)!!, which makes it more attractive for nonlinear processes than both coherent and thermal light.
For the generation of optical harmonics we used broadband parametric down conversion around frequency-degeneracy (1600 nm) produced in 1cm BBO crystal from Ti:Sapphire laser (800 nm, 1.6ps, 5kHz, 3W mean intensity). Due to spectral filtering and post-selection technique we could vary the statistics of light from coherent to super-bunched, which allowed us to demonstrate the efficiency enhancement for second-, third-, and fourth-harmonic generation. The obtained experimental results show a good agreement with the theory.
Organic microstructures attract much attention due to their unique properties originating from the design of their shape and optical parameters. In this work we discuss the linear, second- and third-order nonlinear optical effects in arrays and in individual organic microstructures composed by self-assembling technique and formed randomly on top of a solid substrate. The structures under study consist of micro-spheres, -hemispheres or -frustums made of red laser dye and reveal an intense fluorescence (FL) in the visible spectral range. Importantly, that due to a high value of the refractive index and confined geometry, such micro-structures support the excitation of whispering gallery modes (WGM), which brings about strong and spectrally-selected light localization. We show that an amplification of the nonlinear optical effects is observed for these structures as compared to a homogeneous dye film of similar composition. The obtained data are in agreement with the results of the FDTD calculations performed for the structures of different dimensions. Perspectives of application of such type of organic nonlinear microresonators in optical devices are discussed.
The Borrmann effect is known as an increase of the X-rays transmission of a perfect crystal in the Laue diffraction scheme when the Bragg diffraction condition are satisfied. Following the trend of the transfer of the X-ray phenomena into the optical spectral range, we experimentally observed and studied the optical analogue of the Borrmann effect for the case of one-dimensional photonic crystals (PhC). For the experiments we made the samples of PhCs based on porous fused silica, which reveal periodical modulation of the refractive index and light absorption. We show that in such structures the Borrmann effect reveals itself as increasing transmission when light propagates through a PhC at the Bragg angle of incidence. Pronounced differences of the Borrmann effect are observed for the PhC structures with light losses concentrated in high or low refractive index layers. The spectral features of the effect are analyzed both experimentally and theoretically.
An ideal diagnostic device should be inexpensive, easy-to-use, rapid and reliable. Nanostructured porous silicon (PSi) satisfies these criterions including label-free optical detection and high throughput detection. Pore morphology (size, porosity) must be tailored for each specific application, and for immunosensing applications PSi morphology has been optimized for maximal pore infiltration of larger proteins as immuno gamma globlulin (IgG). Sensor degradation by high salt concentration induces a baseline drift. Different thermal oxidation procedures have been studied in order to obtain a stable sensor in the 3 hour incubation period of the immunoassay with negligible drift
Electronic Kerr effect in a polyfluorene derivative is used to reversibly switch near infrared probe beam resonantly
coupled to a hybrid polymer-silica microspherical resonator. NIR pumping at 780 nm in pulsed laser regime is used for
non-linear switching of the WGM resonances that shift as much as 2 GHz for 50 mW of average pump power, compared
to a shift of 250 MHz for the same average pump power at CW regime. The absence of temporal drift and the magnitude
of this shift confirm the Kerr nature of the switching, ruling out thermooptical effects.
A colorimetric resonant mesoporous silicon photonic crystal is used as a surface binding platform for biochemical
detection. The photonic crystal, when illuminated with white light at normal incidence, is designed to reflect a photonic
band gap (PBG) centered at a single wavelength. When molecules are attached to the internal surfaces of pores, the PBG
is shifted due to the change in refractive index of the porous silicon layers. The planar structure of the platform can be
easily integrated into a fluidic cell. We have optically verified the presence of proteins and chemicals as a colorimetric
shift in the reflectivity spectrum of mesoporous silicon photonic crystals and microcavities.
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.
This work describes the infiltration of a polymeric solution into porous Si structures towards the fabrication of
tunable photonic crystals (PC) and microcavities for photonics applications. The tunability is achieved by infiltrating the
porous silicon based PCs by active organic materials, such as an emissive and nonlinear polymer called 2-methoxy-5-(2-
ethylhexyloxy)-p-phenylenevinylene (namely MEH-PPV). This preliminary work shows the infiltration of this polymeric
solution into PC based on macroporous Si structure as well as in microcavities based on multiple layers of microporous
Si. The solidification of the polymer was obtained by the evaporation of the solvent. Various techniques of infiltration
were studied to obtain an optimized filling of the pores. The infiltration was then characterized using photoluminescence
measurements. Finally, we will report on the study of third harmonic generation (THG) in samples of porous silicon
microcavity infiltrated with MEHPPV. The k-domain THG spectroscopy was applied and an increase of the THG
intensity up to an order of magnitude was achieved for the filled microcavity.
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.
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.
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.
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.
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.
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