Harmonic Generation Method Research Articles

Characterization of domain distributions by second harmonic generation in ferroelectrics

Domain orientations and their volume ratios in ferroelectrics are recognized as a compelling topic recently for domain switching dynamics and domain stability in devices application. Here, an optimized second harmonic generation method has been explored for ferroelectric domain characterization. Combing a unique theoretical model with azimuth-polarization-dependent second harmonic generation response, the complex domain components and their distributions can be rigidly determined in ferroelectric thin films. Using the proposed model, the domain structures of rhombohedral BiFeO3 films with 71° and 109° domain wall, and, tetragonal BiFeO3, Pb(Zr0.2Ti0.8)O3, and BaTiO3 ferroelectric thin films are analyzed and the corresponding polarization variants are determined. This work could provide a powerful and all-optical method to track and evaluate the evolution of ferroelectric domains in the ferroelectric-based devices.

Relationship between the Structure and Nonlinear Optical Properties of R[UO2L3] and R3[UO2L3]4 Crystals (L—Carboxylate Ion)

The nonlinear optical activity (Q) of uranyl carboxylates containing [UO2(L)3]– complexes in the crystal structure, where L is the anion of aliphatic or unsaturated monocarboxylic acids, has been characterized for the first time by the second harmonic generation method. It has been shown using molecular Voronoi–Dirichlet polyhedra that specific features of the cationic sublattice of U and R atoms in carboxylate structures depend on noncovalent interactions between outer-sphere R+ cations and [UO2(L)3]– complex anions. The existence of a relationship between Q and the magnitude of the vector characterizing the displacement of the uranium atom nucleus from the centroid of its Voronoi–Dirichlet polyhedron in the cation sublattice of U and R atoms is revealed.

Characterization of concentrated and distributed cracks in concrete using a harmonic wave modulation technique

In this work, the damage progression of concrete cracks presented in concentrated form caused by mechanical load and presented in distributed form caused by chemical attack is characterized by a harmonic wave modulation technique. The relative amplitude of sidebands in frequency domain due to the modulation effect of two propagating ultrasonic waves is considered as the damage index for concrete samples. The low frequency signal in this research is a harmonic wave produced by an electromagnetic exciter to avoid the uncertainty of man-made influence previously where the low frequency pulse signal was generated by the instrumented hammer. Both the first order sideband corresponding to classical nonlinearity effect and the second order sideband corresponding to hysteresis nonlinearity effect are simultaneously analyzed through the ultrasonic experiments for damaged samples induced by the sulfate attack and bending tests. The nonlinear parameters present a good distinction between damaged and intact samples for both concentrated cracks and distributed cracks and have an increase in orders of magnitude, showing the well-round feasibility of developed nonlinear wave modulation technique. Furthermore, the nonlinear parameters in the wave modulation technique present an excellent correlation with the nonlinear parameter obtained by the second harmonic generation method for bending cracks of the same reinforced concrete, indicating that the wave modulation method is capable of discriminating different state of damage presented in concentrated cracking form.

Influence of doping materials on third harmonic generation in zinc oxide films

Theoretical investigation of nonlinear frequency conversion in pure ZnO, ZnO:Ag (1.6 at.%) and ZnO:Cu (4.7 at.%) films account for phase effects has been carried out. For this, the constant-intensity approximation of fundamental radiation is applied. The analytical method also lets estimation of the influence of impurities on the nonlinear optical properties of films by third harmonic generation (THG) method and approximation of the maximum value of the third harmonic intensity in pure and doped ZnO by silver and copper films. In this study, the factors which limit the efficiency of the process of conversion of frequency are outlined. Namely, at chosen pump intensity of laser-radiator, it is possible to calculate the coherent length of a crystal-converter. Method of analysis of THG in pure and doped ZnO films, used in the present work, will be extended to other doped nanostructures in future.

Functional 2D nanomaterials for optoelectronics based on langmuir bacteriorhodopsin films

We have tested the possibility of using monomolecular layers of bacteriorhodopsin (BR) for the synthesis of highly sensitive and highly selective sensors based on second harmonic generation and surface plasma waves. We have used various methods to study the optical and nonlinear optical properties of Langmuir-Blodgett films of BR in order to clarify the extent to which specific properties of BR molecules are retained during their transfer from the surface of water to a solid substrate. We show that the second harmonic generation method is efficient for analyzing the molecular orientation and quality of Langmuir-Blodgett films. The experimental nonlinear optical susceptibility of second order BR molecules is 3.4·10−11m/V. The relative change in the resonant wave vector is (3.6±0.1)·10−2 at an excitation light wavelength of 630nm. We have obtained a BR spectrum with the effective excitation by incident radiation of surface plasma waves. On the basis of these studies, we have proposed new schemes of biosensors operating on the basis of second harmonic generation and surface plasma resonance caused by fundamental frequency reflection from BR monomolecular layers. This scheme was tested for a model device and demonstrated the possibility of obtaining sensitivities of the order of 1011 molecules/cm3.

Functional 2D nanomaterials for optoelectronic equipment on the basis of langmuir–blodgett bacteriorhodopsin films

We have tested the possibility of using monomolecular layers of bacteriorhodopsin (BR) for the synthesis of highly sensitive and highly selective sensors based on second harmonic generation and surface plasma waves. We have used various methods to study the optical and nonlinear optical properties of Langmuir-Blodgett films of BR in order to clarify the extent to which specific properties of BR molecules are retained during their transfer from the surface of water to a solid substrate. We show that the second harmonic generation method is efficient for analyzing the molecular orientation and quality of Langmuir-Blodgett films. The experimental nonlinear optical susceptibility of second order BR molecules is 3.4 · 10-11m/V. The relative change in the resonant wave vector is (3.6 ± 0.1)·10-2at an excitation light wavelength of 630 nm. We have obtained a BR spectrum with the effective excitation by incident radiation of surface plasma waves. On the basis of these studies, we have proposed new schemes of biosensors operating on the basis of second harmonic generation and surface plasma resonance caused by fundamental frequency reflection from BR monomolecular layers. This scheme was tested for a model device and demonstrated the possibility of obtaining sensitivities of the order of 1011molecules/cm3.

Influence of NaCl/LiF Additives on Structure, Microstructure and Phase Transitions of (K0.5Na0.5)NbO3 Ceramics

Influence of NaCl/LiF additives (with molar ratio of 0.58:0.42) on phase formation, unit cell parameters, microstructure, dielectric and ferroelectric properties of (K0.5Na0.5)NbO3 ceramics has been studied. Intensification of the sintering process and a decrease in the unit cell parameters were proved. Enhancement of ferroelectric properties and an increase in the Curie temperature value stimulated by the additives were revealed using the Dielectric Spectroscopy and Second Harmonic Generation methods.

Design and Preparation of Novel D-Pi-A Molecule with Flexible Isolated Groups in Both Sides

Novel nonlinear optical chromophore with strong electron donor and isolation groups on both sides were synthesized and characterized by mass spectrum and hydrogen nuclear magnetic resonance. Reactive groups were introduced to the isolation groups which could both improve the chromophore's electro optic activity and make the chromophore be easily reacted wth other monomers or polymers. Electro-optical polymers with different chromophore loading densities were prepared and showed us good thermal stabilities, all of their thermal decomposition temperatures were higher than 250°C. Large EO coefficients were also gotten by second harmonic generation method 63.1 and 89.3 pm/V for PU-10 and PU-20, respectively. Solvatochromism of polymer PU-10 was also studied; the result indicated to us that this kind of polymers could be used as solvent polarity indicator material.

Nonlinear Attosecond Metrology by Intense Isolated Attosecond Pulses

For the future progress of nonlinear attosecond science, one of the most important issues is the development of high-energy isolated attosecond pulse sources. In this paper, we review our research on the energy-scaling method for isolated attosecond pulse generation, which combines infrared two-color gating and an energy-scaling method of high-order harmonic generation. By establishing the robust energy-scaling method, the maximum pulse energy of the isolated attosecond pulse reaches 1.3 $\mu$ J/pulse in the XUV region, which is almost 100-fold higher than the values ever reported before. The pulse duration of this isolated attosecond pulse is directly measured to be 500 as by the autocorrelation method using the nonlinear interaction of N $_2$ . This nonlinear experiment clearly shows that our developed isolated attosecond pulse has enough pulse energy to make a breakthrough for nonlinear attosecond metrology as well as for attosecond-pump/attosecond-probe experiments investigating electronic processes. In addition, we further extend the high-energy harmonic continuum by using the infrared two-color gating method up to the soft-x-ray region. With the aim to temporally characterize an isolated attosecond pulse in the soft-x-ray region, we demonstrate the first observation of above-threshold ionization of He with two-photon absorption of multiple higher harmonics in the soft-x-ray region.

ChemInform Abstract: Styryl‐Based NLO Chromophores: Synthesis, Spectroscopic Properties, and Theoretical Calculations.

AbstractA series of styryl‐based push‐pull chromophores are synthesized.

δ-BiB3O6:Pr3+: polymer nanocomposites deposited on substrates with silver nanoparticles for nonlinear optics

Composites containing nanocrystallites of novel rare earth doped borate δ-BiB3O6 and polyvinyl alcohol (PVA) polymer are reported. Experimental studies of the third-order nonlinear refractive index n2, absorption coefficient β and second-order nonlinearity for δ-BiB3O6:Pr3+(7.5 at.%) large-size nanocrystallites embedded into PVA polymer matrices and deposited on gallium-doped zinc oxide substrates modified with silver nanoparticles (Ag-NPs) using Z-scan technique and second harmonic generation (SHG) method were performed. The complex SHG and Z-scan measurements for different sizes of Ag-NPs were done. It was shown that the polymer composite of PVA containing particles of orthorhombic bismuth triborate doped with praseodymium (7.5 at.%) reveals optically nonlinear response. It was shown that the studied composites possess both coherent and non-coherent component of nonlinear optics. The Z-scan measurements were done with use of 5 ns Nd:YAG laser and the second harmonic generation was measured using the 25 ns Nd:YAG laser with frequency repetition about 10 Hz. The measurements showed that both second as well as third-order susceptibilities are sensitive to the sizes of the Ag-NPs. The obtained results confirm a principal role of the Ag-NPs in influencing the output susceptibilities.

Design and preparation of novel diazo chromophores with flexible isolated groups

Novel nonlinear optical chromophore with strong electron donor, diazo electron bridge and isolation groups on both sides were synthesized and characterized by mass spectrum and hydrogen nuclear magnetic resonance. Strong electron donor and diazo electron bridge improve the nonlinear optical activities of the chromophore, large and reactive isolated groups improve the chromophore’s solubility and reduced the interaction among the chromophores. Second order nonlinear optical polymers with different chromophore loading densities were prepared and showed us the smallest glass transition temperature change. Large second order nonlinear optical coefficients were also gotten by second harmonic generation method 15.3, 27.2 and 33.4 pm/V for chromophore loading density at 10, 22.5 and 27.5 wt% respectively.

Styryl-based NLO chromophores: synthesis, spectroscopic properties, and theoretical calculations

A novel series of styryl-based chromophores is synthesized, the constituents of which are characterized by UV–Vis, NMR, mass spectrometry, and thermal analysis. The chromophores show good solubility in MeOH, THF, and CH2Cl2. They also show good thermal stability for practical applications. Density functional theory calculations are employed in order to ascertain the structural, molecular, and electronic properties of the dyes. Moreover, the second order nonlinear optical (NLO) responses of the dyes are measured by the electric field induced second harmonic (EFISH) generation method. Relatively high scalar products of the vector component of the first hyperpolarizability tensor and the dipole moment vector (μβ) are obtained for some of the compounds.

Tunable enhancement of ferroelectric properties in BaxSr1−xTiO3/La0.7Sr0.3MgO3 heterostructures observed by means of second harmonic generation technique

This work is devoted to research an influence of Ba cation concentration on polarization properties of ferroelectric layer which is included in bilayer structures as functional stratum. We have created bilayer nanocomposites consisting of a ferroelectric Ba(x)Sr(1−x)TiO3 (BST) layer and a ferromagnetic La0.7Sr0.3MnO3 (LSMO) layer with various concentrations of Ba. The epitaxial heterostructure BST/LSMO was fabricated using metal-organic aerosol deposition technique (MAD) on a single-crystal substrate SrTiO3 (001). The structural parameters of the BST/LSMO were defined by X-ray diffraction analysis. The in-plane ferroelectric polarization, measured by means of optical second harmonic generation (SHG) method, was shown to be strongly dependent on the Ba concentration. We consider this effect as structural distortion at room temperatures which close to the structural phase transition and altering the Ba concentration affects the vicinity to the phase transition point.

Does Cell Shape Determine Cell Fate?

Different types of cells, i.e. from different tissues, typically look quite different from each other. Even when cultured on two-dimensional surfaces like glass slides or tissue culture polystyrene under identical conditions, cells adopt different shapes. These shapes are in general functions of the cytoskeletal properties of those cells, itself a subset of what we call the “state” of the cell. Moreover the changes in cell shape upon perturbation of the surface or of the cells themselves should reflect their intrinsic cellular properties, i.e. the cell state. Significant evidence has accumulated that changes in shape can also alter cellular properties, at least for some cells. Our experiments suggest that for Mesenchymal Stem Cells (MSCs), shape perturbations have consequences for their differentiation into osteoblasts. Thus shape seemed linked to fate. These statements beg the question: is it possible to use cell shape to assess cell state? For example can we back-calculate the cytoskeletal properties of the cell from the way it looks on surfaces? This question becomes all the more interesting for cancer cells since cancer cells are known to have altered mechanical properties compared to normal cells, and invasive cancer cells appear to have altered mechanical properties compared to non-invasive cancer cells. In this work we present a combination of experiments and statistical data analysis to try to begin to understand how cell shapes are affected by changes in surface properties or by perturbations of the cytoskeleton. We use fluorescent imaging to obtain the two-dimensional profile of cells and novel Third Harmonic Generation methods to obtain three-dimensional images on cells on substrates. We use these experiments to infer how the cell shape of cancer cells could be associated with their invasive properties. We discuss some rudimentary mathematical models based on these results.

Improvement of the quadratic non-linear optical properties of pyrimidine chromophores by N-methylation and tungsten pentacarbonyl complexation

In this contribution, we report the synthesis of two series of compounds: 4-(arylvinyl)-1-methylpyrimidinium derivatives and tungsten pentacarbonyl complexes of 4-(arylvinyl)pyrimidines. Their second order non-linear properties, measured by Electric-Field Induced Second Harmonic generation (EFISH) method, and their photophysical behavior were thoroughly investigated and compared to the corresponding 4-(arylvinyl)pyrimidines. A strong enhancement of the NLO response was observed upon methylation or complexation by W(CO)5 of the pyrimidine ring. DFT theoretical calculations were performed to provide complementary insights on the structure-properties relationships in particular concerning the amplitude of the NLO response.

Second- and third-order nonlinear optical properties of bis-chalcone derivatives

• 2,5-Bis(4-methoxy-benzylidene)-cyclopentanone (CP-POME) showed very high second harmonic generation (SHG) efficiency (5.3 times than that of urea). • All the compounds showed good third order NLO property. 2,5-Bis(cinnamylidene)-cyclopentanone (CP-CAL) exhibited good NLA activity with β coefficient of 1 × 10 −10 m/W. • The NLA observed in the present study is of two photon absorption (2PA) and optical limiting type. • The compounds can have potential applications in sensor and eye protection. Bis-chalcone derivatives: 2,5-bis(benzylidene)-cyclopentanone (CP-DBA), 2,5-bis(4-methoxy-benzylidene)-cyclopentanone (CP-POME), 2,5-bis(4-isopropyl-benzylidene)-cyclopentanone (CP-ISO) and 2,5-bis(cinnamylidene)-cyclopentanone (CP-CAL) are synthesized by Claisen–Schmidt reaction and characterized using, FT-IR, 1 H NMR, 13 C NMR, and mass spectroscopic techniques. The second- and third-order nonlinear optical properties of these samples are studied using second harmonic generation and nanosecond open-aperture Z-scan methods. CP-POME has shown a very high second harmonic generation (SHG) efficiency (5.3 times that of urea). These molecules reveal a strong third-order nonlinear absorption (NLA) that is of optical limiting type, due to their peculiar D–π–A–π–D structure that leads to high polarization of the delocalized electron cloud. CP-CAL exhibits highest NLA activity with a β coefficient of 1 × 10 −10 m/W. Through numerical simulations, the mechanism of NLA is found to be a two-photon absorption process in the case of all the samples.

Synthesis of Y-type Polyurethanes Containing Novel NLO Chromophore

Novel nonlinear optical chromophore with strong electron donor and isolation groups on both sides were synthesized and characterized by mass spectrum and hydrogen nuclear magnetic resonance. Electro-optical polymers with different chromophore loading densities were prepared and showed us good thermal stabilities, all of their thermal decomposition temperature were higher than 250°C. Large EO coefficients were also obtained by second harmonic generation method 29, 47, and 72 pm/V for PU-C10, PU-C15, and PU-C20, respectively. Solvatochromism of polymer PU-C10 was also studied; the result indicated us that this kind of polymers could be used as solvent polarity indicator material.

Synthesis of novel D–Pi–A chromophore with two reactive groups in the middle section

D–Pi–A chromophore with strong electron donor and isolated groups on both sides was synthesized and characterized by mass spectrum and hydrogen nuclear magnetic resonance. Reactive groups, which could both improve the chromophore’s electro optic activity and make the chromophore be easily reacted with other monomers or polymers, were introduced to the middle section of the chromophore. Electro-optical (EO) polymers with different chromophore loading densities were prepared and all of them showed us good thermal stabilities, their thermal decomposition temperatures were all higher than 275 °C. Large EO coefficients were also gotten by second harmonic generation method, 58, 76 and 91 pm/V respectively for PU-C10, PU-C15 and PU-C20. Solvatochromism of polymer PU-C10 was studied; the result indicated us that this kind of polymers could be used as solvent polarity indicators.

Arterial Extracellular Matrix: A Mechanobiological Study of the Contributions and Interactions of Elastin and Collagen

The complex network structure of elastin and collagen extracellular matrix (ECM) forms the primary load bearing components in the arterial wall. The structural and mechanobiological interactions between elastin and collagen are important for properly functioning arteries. Here, we examined the elastin and collagen organization, realignment, and recruitment by coupling mechanical loading and multiphoton imaging. Two-photon excitation fluorescence and second harmonic generation methods were performed with a multiphoton video-rate microscope to capture real time changes to the elastin and collagen structure during biaxial deformation. Enzymatic removal of elastin was performed to assess the structural changes of the remaining collagen structure. Quantitative analysis of the structural changes to elastin and collagen was made using a combination of two-dimensional fast Fourier transform and fractal analysis, which allows for a more complete understanding of structural changes. Our study provides new quantitative evidence, to our knowledge on the sequential engagement of different arterial ECM components in response to mechanical loading. The adventitial collagen exists as large wavy bundles of fibers that exhibit fiber engagement after 20% strain. The medial collagen is engaged throughout the stretching process, and prominent elastic fiber engagement is observed up to 20% strain after which the engagement plateaus. The fiber orientation distribution functions show remarkably different changes in the ECM structure in response to mechanical loading. The medial collagen shows an evident preferred circumferential distribution, however the fiber families of adventitial collagen are obscured by their waviness at no or low mechanical strains. Collagen fibers in both layers exhibit significant realignment in response to unequal biaxial loading. The elastic fibers are much more uniformly distributed and remained relatively unchanged due to loading. Removal of elastin produces similar structural changes in collagen as mechanical loading. Our study suggests that the elastic fibers are under tension and impart an intrinsic compressive stress on the collagen.