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Harmonic Generation (harmonic + generation)
Kinds of Harmonic Generation Selected AbstractsObservation of interfacial electrostatic field-induced changes in the silicon dielectric function using spectroscopic ellipsometryPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2008J. Price Abstract This work investigates the capability of spectroscopic ellipsometry to measure charge trapping centers in thin dielectric films. Specific interfacial electrostatic fields, induced by electrons injected into charge trapping states at the interface, have been identified that directly affect the underlying silicon substrate critical points. The effect of a field-induced change in the silicon fundamental absorption edge due to different processing conditions affecting the oxygen vacancy defects at the interface is presented. Measuring the field-induced change in the silicon dielectric function between a sample with a 2 nm HfO2 film as-deposited and the same sample after a 1000 °C anneal in an N2 ambient reveals that a stronger interfacial field is present for the as-deposited HfO2 film. These results are consistent with the understanding that high temperature anneals work well to passivate oxygen vacancy defects at the silicon/HfO2 interface. Finally, we compare our results with Second Harmonic Generation where specific resonant features are identifiable with electric field enhancements at the same interface. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of quadratic contributions in magnetization-induced second harmonic generation studies of magnetization reversalPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2005V. K. Valev Abstract Magnetization-induced optical Second Harmonic Generation (MSHG) from an exchange-biased CoO/Fe multilayer produces an asymmetrical hysteresis loop that indicates different magnetization reversal behaviour between the interface and the bulk ferromagnet. A more careful analysis of the data demonstrates that this asymmetry is in fact due to a quadratic dependence on the magnetization of the MSHG intensity. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] ChemInform Abstract: Soluble Semiconductors AAsSe2 (A: Li, Na) with a Direct-Band-Gap and Strong Second Harmonic Generation: A Combined Experimental and Theoretical Study.CHEMINFORM, Issue 24 2010Tarun K. Bera Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: A Polar and Chiral Indium Telluride Featuring Supertetrahedral T2 Clusters and Nonlinear Optical Second Harmonic Generation.CHEMINFORM, Issue 13 2009Qichun Zhang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] The role of the cyclometallated moiety on the second order nonlinear optical properties of cationic Ir(III) organometallic NLO-phoresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S1 2009Claudia Dragonetti Abstract The second order nonlinear optical (NLO) response of the new complexes [Ir(bzq)2(5-R-1,10-phen)][Y] (bzq = cyclometallated benzo[h]quinoline; phen = phenanthroline, R = Me, NO2; Y = PF6, C12H25SO3) and [Ir(bzq)2(4-R,7-R-1,10-phen)][Y] (R = Me, Ph) have been investigated experimentally by the Electric Field Induced Second Harmonic generation (EFISH) technique in CH2Cl2 solution and compared with that of [Ir(ppy)2(5-R-1,10-phen)][PF6] (ppy = cyclometallated 2-phenylpyridine, R = Me, NO2) and [Ir(ppy)2(4-R,7-R-1,10-phen)][PF6] (R = Me, Ph). It appeared that substitution of ppy with the more ,-delocalized bzq does not affect significantly the large second-order NLO response of this class of complexes. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystal growth, crystal structure and physical properties of polar orthorhombic tris(glycine) zinc chlorideCRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2008M. Fleck Abstract Large single crystals of the polar (point group mm 2) compound tris(glycine) zinc chloride, (NH3CH2COO)3 · ZnCl2, were grown from aqueous solutions. The refractive indices were measured in the wavelength region from 365 nm to 1083 nm and an unpolarised absorption spectrum was recorded (transparency range from 260 to 1550nm). The phase matching conditions for second harmonic generation were analysed: both, type I (ss-f) and type II (sf-f) are possible in the red and near IR region. All five components of the piezoelectric tensor [dijk ] were determined; the maximum values of longitudinal and transverse piezoelectric effects are less than one half of d111 of ,-quartz. In addition, a redetermination of the crystal structure (including location of H atoms) is presented. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A perturbation analysis of harmonic generation from saturated elements in power systemsELECTRICAL ENGINEERING IN JAPAN, Issue 4 2010Teruhisa Kumano Abstract Nonlinear phenomena such as saturation of magnetic flux have considerable effects in power systems analysis. It is reported that a failure in a real 500-kV system triggered islanding operation, where resultant even harmonics caused malfunctions in protective relays. It is also reported that the major origin of this wave distortion is nothing but unidirectional magnetization of the transformer iron core. Time simulation is widely used today to analyze phenomena of this type, but it has basically two shortcomings. One is that the time simulation takes too much computing time in the vicinity of inflection points in the saturation characteristic curve because certain iterative procedures such as N-R (Newton,Raphson) must be used and such methods tend to be caught in an ill-conditioned numerical hunting. The other is that such simulation methods sometimes do not aid an intuitive understanding of the studied phenomenon because all of the nonlinear equations are treated in matrix form and are not properly divided into understandable parts, as is done in linear systems. This paper proposes a new computation scheme that is based on the so-called perturbation method. Magnetic saturation of iron cores in a generator and a transformer are taken into account. The proposed method has a special feature to deal with the first shortcoming of the N-R-based time simulation method stated above. The proposed method does not use an iterative process to reduce the equation residue, but uses perturbation series, so that it is free of the ill-conditioning problem. The user need only calculate the perturbation terms one by one until the necessary accuracy is attained. In a numerical example treated in the present paper, first-order perturbation can achieve reasonably high accuracy, which means very fast computing time. In a numerical study, three nonlinear elements are considered. The calculation results are almost identical to the conventional N-R-based time simulation, which shows the validity of the method. The proposed method can be effectively used in screening where many case studies are needed. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(4): 35,42, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20895 [source] Quantified characterization of human cutaneous normal scar using multiphoton microscopyJOURNAL OF BIOPHOTONICS, Issue 1-2 2010Xiaoqin Zhu Abstract The morphological alterations of human cutaneous normal scar were quantitatively analyzed using multiphoton microscopy (MPM) based on two-photon excited fluorescence and second harmonic generation. High-contrast, high-resolution images of normal scar and uninjured skin were obtained for comparison. In addition, some quantitative parameters have been extracted to quantitatively discriminate between normal scar and uninjured skin. The MPM combined with quantitative method enable a better understanding of microstructual alterations of the epidermis, elastic fiber, and collagen in normal scar. It may lead the way to making know the mechanism of normal scar formation and identifying feasible therapeutic options. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis and second-order nonlinear optical properties of multifunctional polysiloxanes with sulfonyl-based chromophoresJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2005Jianli Hua Abstract Two new polysiloxanes (P1 and P2) with a high density of sulfonyl-based chromophores were prepared by a new two-step method. Poly[methyl-3-(9-carbazolyl)propyl siloxane] was partially formulated by the standard Vilsmeier reaction, and formyl groups of high reactivity were condensed with cyanoacetylated chromophores; this yielded polysiloxanes P1 and P2 in almost complete conversions. Their structures were verified with 1H NMR, IR, and ultraviolet,visible spectra. P1 and P2 exhibited good solubility in common organic solvents and were thermally stable. The maximum absorptions appeared at about 452 and 390 nm for P1 and P2, respectively, in tetrahydrofuran; they were blueshifted about 42 and 8 nm, respectively, in comparison with those of the corresponding chromophores with a nitro acceptor and resulted in a wider transparency window. The P1 values of the nonlinear optical coefficient (d33), measured by in situ second harmonic generation, was 16.2 pm/V. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1317,1324, 2005 [source] Anomalous behavior of the second and third harmonics generated by femtosecond Cr:forsterite laser pulses in SiC,polymer nanocomposite materials as functions of the SiC nanopowder contentJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2003S. O. Konorov Abstract Femtosecond pulses of 1.25 µm Cr:forsterite laser radiation were used to study second- and third-harmonic generation in silicon carbide nanopowders embedded in a poly(methyl methacrylate) (PMMA) film. Harmonic generation processes extend the analytical and sensing abilities of light-scattering techniques, including Raman spectroscopy, offering a convenient and efficient approach to the analysis of nanocomposite materials where nanoparticles tend to agglomerate, masking informative features in Raman spectra. The second- and third-harmonic yields are shown to display an anomalous, counterintuitive behavior as functions of the SiC nanopowder content in a polymer film. Whereas harmonic generation in polymer films with a high content of SiC nanocrystals is quenched by the absorption of agglomerating nanoparticles, the influence of absorption is less detrimental in nanocomposite films with a lower SiC content, leading to the growth of the second- and third-harmonic yields. Nanocomposite films with a lower SiC content are also characterized by a higher breakdown threshold, allowing pump pulses with higher fluences to be applied for more efficient harmonic generation. Copyright © 2003 John Wiley & Sons, Ltd. [source] Nonlinear-laser ,(3) -effects in novel garnet-type fine-grained ceramic-host {YGd2}[Sc2](Al2Ga)O12 for Ln3+ lasantsLASER PHYSICS LETTERS, Issue 9 2009A.A. Kaminskii Abstract We report on ,(3) -nonlinear generation in crystalline ceramics {YGd2}[Sc2](Al2Ga)O12 offering partly disordered garnet structure, namely octave-spanning Stokes and anti-Stokes lasing comb and third harmonic generation under one-micron picosecond pumping. Possibilities for creation of really disordered laser "garnet"-type ceramics is discussed. (© 2009 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Tetragonal Ba2MgGe2O7 , a novel multifunctional optical crystal with numerous manifestations of nonlinear-laser effects: almost sesqui-octave Stokes and anti-Stokes combs and cascaded ,(3),,(2) lasing with involved second and third harmonic generationLASER PHYSICS LETTERS, Issue 12 2008A.A. Kaminskii Abstract Melilite-type Ba2MgGe2O7 was found to be an attractive, simultaneously ,(2) - and ,(3) -active nonlinear optical crystal. Under one-micron picosecond pumping we observed several manifestations of nonlinear interactions, namely almost sesqui-octave Stokes and anti-Stokes lasing combs, collinear and "Cherenkov"-type SHG, THG, SFG, and cascaded selfconversion ,(3),,(2) generation in the visible and UV range. All recorded lasing components were identified and attributed to a single SRS-promoting vibration mode ,SRS = 771.5 cm,1. A short review of melilite-type compounds is given. (© 2008 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Influence of the intracavity second harmonic generation on the mode competition in a double-mode diode-pumped Nd:YAG laserLASER PHYSICS LETTERS, Issue 7 2005V. M. Yermachenko Abstract The influence of intracavity second harmonic generation on the mode competition in a double-mode diode-pumped Nd:YAG laser is studied theoretically and experimentally. Various configurations of the optical cavity with II-type phasematching frequency-doubling crystals are considered. The conditions of steady-state lasing and of lasing with a small level of amplitude pulsation in the output laser beam are determined. (© 2005 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Symmetry point group description of second harmonic generation in carbon nanotubesLASER PHYSICS LETTERS, Issue 4 2004L. De Dominicis Abstract The role played by symmetry properties of a carbon nanotube in the generation of second harmonic radiation is studied by using the formalism of irreducible representation of the symmetry point group. Experimental results of second harmonic generation in a carbon nanotube sample are discusses in view of the theoretical prediction obtained. (© 2004 by ASTRO, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Clinical two-photon microendoscopyMICROSCOPY RESEARCH AND TECHNIQUE, Issue 5 2007K. König Abstract Two-photon medical imaging has found its way into dermatology as an excellent method for noninvasive skin cancer detection without need of contrast agents as well as for in situ drug screening of topically-applied cosmetical and pharmaceutical components. There is an increasing demand to apply the multiphoton technology also for deep-tissue skin imaging as well as for intracorporal imaging. We report on the first clinical use of multiphoton endoscopes, in particular of a miniaturized rigid two-photon GRIN lens endoscope. The microendoscope was attached to the multiphoton tomograph DermaInspect and employed to detect the extracellular matrix proteins collagen and elastin in the human dermis of volunteers and patients with ulcera by in vivo second harmonic generation and in vivo two-photon autofluorescence. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source] Intact corneal stroma visualization of GFP mouse revealed by multiphoton imagingMICROSCOPY RESEARCH AND TECHNIQUE, Issue 12 2006Wen Lo Abstract The aim of this work is to demonstrate that multiphoton microscopy is a preferred technique to investigate intact cornea structure without slicing and staining. At the micron resolution, multiphoton imaging can provide both large morphological features and detailed structure of epithelium, corneal collagen fibril bundles and keratocytes. A large area multiphoton cross-section across an intact eye excised from a GFP mouse was obtained by a homebuilt multiphoton microscope. The broadband multiphoton fluorescence (435,700 nm) and second harmonic generation (SHG, 360,400 nm) signals were generated by the 760 nm output of a femtosecond titanium-sapphire laser. A water immersion objective (Fluor Ô, 40X, NA 0.8; Nikon) was used to facilitate imaging the curve ocular surface. The multiphoton image over entire cornea provides morphological information of epithelial cells, keratocytes, and global collagen orientation. Specifically, our planar, large area multiphoton image reveals a concentric pattern of the stroma collagen, indicative of the laminar collagen organization throughout the stroma. In addition, the green fluorescence protein (GFP) labeling contributed to fluorescence contrast of cellular area and facilitated visualizing of inactive keratocytes. Our results show that multiphoton imaging of GFP labeled mouse cornea manifests both morphological significance and structural details. The second harmonic generation imaging reveals the collagen orientation, while the multiphoton fluorescence imaging indicates morphology and distribution of cells in cornea. Our results support that multiphoton microscopy is an appropriate technology for further in vivo investigation and diagnosis of cornea. Microsc. Res. Tech., 2006. © 2006 Wiley-Liss, Inc. [source] Study of Nonlinear Optical Properties of Multilayer Langmuir,Blodgett Films Containing Bacteriorhodopsin,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2000Yu. O. Barmenkov ABSTRACT Multilayer oriented Langmuir,Blodgett films of bacteriorhodopsin were prepared and their nonlinear optical properties, including second harmonic generation and photoresponse at a two phase-modulated beams mixing, were investigated. The nonlinear component of refractive index of the films was measured. [source] Enhancement of nonlinear optical properties of Au,TiO2 granular composite with high percolation thresholdPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2008Z. K. Zhou Abstract Two series of Au,TiO2 composite films with Au percola- tion threshold qC of 0.34 and 0.82 were prepared by using sputtering technique at the pressure of 5.0 × 10,2 and 8.0 × 10,2 Torr, respectively. As qC increases from 0.34 to 0.82, the plasmon resonant absorption of the composite films near qC shifts from about 700 nm to 760 nm, and the maximal second harmonic generation (SHG) intensity increases by 20%, the maximal nonlinear absorption coefficient increases from ,3.0 × 104 cm/GW to 1.7 × 105 cm/GW, and the maximal nonlinear refraction index increases from a very small value to ,2.6 cm2/GW. The large second- and third-order optical nonlinearity of the Au,TiO2 composite films with high qC is attributed to the high density of Au particle in the nonconductive film and the strong local field enhancement caused by the surface plasmon resonant absorption. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Second harmonic generation spectroscopy on Si surfaces and interfacesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2010Kjeld Pedersen Abstract Optical second harmonic generation (SHG) spectroscopy studies of Si(111) surfaces and interfaces are reviewed for two types of systems: (1) clean 7,×,7 and -Ag reconstructed surfaces prepared under ultra-high vacuum conditions where surface states are excited and (2) interfaces in silicon-on-insulator (SOI) structures and thin metal films on Si surfaces where several interfaces contribute to the SHG. In all the systems resonances are seen at interband transitions near the bulk critical points E1 and E2. On the clean surfaces a number of resonances appear below the onset of bulk-like interband transitions that can be referred to excitations of dangling bond surface states. Adsorption of oxygen leads to formation of a new surface resonance. Such resonances appearing in the region between the bulk critical points E1 and E2 are also shown to be important for Si/oxide interfaces in SOI structures. Finally, examples of spectroscopy on layers buried below thin Ag and Au films are given. [source] Second harmonic generation in centrosymmetric transition-metal oxidesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2005Georgios Lefkidis Abstract Second harmonic generation is a powerful tool for monitoring ultrafast dynamics and investigating domain structures in transition-metal oxides. A symmetry analysis of the contributions to the second order susceptibility tensor of different antiferromagnetic domains is performed, and the role of the phonons is discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Phenomenology of magnetic second harmonic generation from low symmetry surfaces and interfacesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2003L. Carroll Abstract Low dimensional magnetic structures show interesting and novel phenomena such as oscillatory magnetic coupling and giant magnetoresistance. Magnetic second harmonic generation (MSHG) can provide unique information on magnetic surfaces and interfaces because, within the dipole approximation, broken space-inversion symmetry at the surface or interface of centrosymmetric media, and broken time-reversal symmetry arising from the magnetization, are both required in order to observe a magnetic-field-dependent second harmonic response. However, the additional reduction in symmetry arising from the magetization produces many non-zero susceptibility tensor components, particularly in the case of vicinal, stepped surfaces of 1m symmetry, and care is needed in designing experiments that will produce readily interpretable results. Phenomenological expressions for the MSHG response from systems of 1m symmetry are presented, where combinations of input and output polarizations and magnetic field orientations allow the essential physics of these systems to be explored, particularly in relation to distinguishing terrace and step contributions to the magnetization from vicinal surfaces and interfaces. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High harmonic generation by two color field-mixing in n-type low-doped GaAsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2003D. Persano Adorno Abstract Monte Carlo simulations for high harmonic generation by two mixed electric fields linearly polarized with frequency in the far-infrared range in GaAs crystal are examined. The wave-mixed signal conversion efficiency is calculated by the use of the appropriate Maxwell equation for the propagation of an electromagnetic wave along a given direction in a medium. We show how the efficiency of the harmonics and their polarization depend on: (i) the frequencies and the intensities of the incident waves; (ii) the angle between the polarization of the two incident fields. [source] Cation movement and phase transitions in KTP isostructures; X-ray study of sodium-doped KTP at 10.5,KACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2003Stefan T. Norberg An accurate structure model of sodium-doped potassium titanyl phosphate, (Na0.114K0.886)K(TiO)2(PO4)2, has been determined at 10.5,K by single-crystal X-ray diffraction. In addition to the low-temperature data, X-ray intensities have been collected at room temperature. When the temperature was decreased from room temperature to 10.5,K, both potassium cations moved 0.033,(2),Å along the c -axis, i.e. in the polar direction within the rigid Ti,O,P network. This alkaline metal ion displacement can be related to the Abrahams,Jamieson,Kurtz TC criteria for oxygen framework ferroelectrics. Potassium titanyl phosphate (KTP) is a well known material for second harmonic generation (SHG), and the influence of sodium dopant on the TiO6 octahedral geometry and SHG is discussed. The material studied crystallizes in the space group Pna21 with Z = 4, a = 12.7919,(5), b = 6.3798,(4), c = 10.5880,(7),Å, V = 864.08,(9),Å3, T = 10.5,(3),K and R = 0.023. [source] Investigation of the structure and phase transitions in the novel A-site substituted distorted perovskite compound Na0.5Bi0.5TiO3ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2002G. O. Jones Rietveld neutron powder profile analysis of the compound Na0.5Bi0.5TiO3 (NBT) is reported over the temperature range 5,873,K. The sequence of phase transitions from the high-temperature prototypic cubic structure (above 813,K), to one of tetragonal (673,773,K) and then rhombohedral structures (5,528,K) has been established. Coexisting tetragonal/cubic (773,813,K) and rhombohedral/tetragonal (with an upper temperature limit of 145,K between 528 and 673,K) phases have also been observed. Refinements have revealed that the rhombohedral phase, space group R3c, with aH = 5.4887,(2), cH = 13.5048,(8),Å, V = 352.33,(3),Å3, Z = 6 and Dx = 5.99,Mg,m,3, exhibits an antiphase, a,a,a, oxygen tilt system, , = 8.24,(4)°, with parallel cation displacements at room temperature. The tetragonal phase, space group P4bm, with aT = 5.5179,(2), cT = 3.9073,(2),Å, V = 118.96,(1),Å3, Z = 2 and Dx = 5.91,Mg,m,3, possesses an unusual combination of in-phase, a0a0c+ oxygen octahedra tilts, , = 3.06,(2)°, and antiparallel cation displacements along the polar axis. General trends of cation displacements and the various deviations of the octahedral network from the prototypic cubic perovskite structure have been established and their systematic behaviour with temperature is reported. An investigation of phase transition behaviour using second harmonic generation (SHG) to establish the centrosymmetric or non-centrosymmetric nature of the various phases is also reported. [source] Einstein Lecture , Passion for precision,ANNALEN DER PHYSIK, Issue 9 2006T.W. Hänsch Abstract Optical frequency combs from mode-locked femtosecond lasers have link optical and microwave frequencies in a single step, and they provide the long missing clockwork for optical atomic clocks. By extending the limits of time and frequency metrology, they enable new tests of fundamental physics laws. Precise comparisons of optical resonance frequencies of atomic hydrogen and other atoms with the microwave frequency of a cesium atomic clock are establishing sensitive limits for possible slow variations of fundamental constants. Optical high harmonic generation is extending frequency comb techniques into the extreme ultraviolet, opening a new spectral territory to precision laser spectroscopy. Frequency comb techniques are also providing a key to attosecond science by offering control of the electric field of ultrafast laser pulses. In our laboratories at Stanford and Garching, the development of new instruments and techniques for precision laser spectroscopy has long been motivated by the goal of ever higher resolution and measurement accuracy in optical spectroscopy of the simple hydrogen atom which permits unique confrontations between experiment and fundamental theory. This lecture recounts these adventures and the evolution of laser frequency comb techniques from my personal perspective. [source] Calcite microcrystals in the pineal gland of the human brain: First physical and chemical studiesBIOELECTROMAGNETICS, Issue 7 2002Simon Baconnier Abstract A new form of biomineralization has been studied in the pineal gland of the human brain. It consists of small crystals that are less than 20 ,m in length and that are completely distinct from the often observed mulberry-type hydroxyapatite concretions. A special procedure was developed for isolation of the crystals from the organic matter in the pineal gland. Cubic, hexagonal, and cylindrical morphologies have been identified using scanning electron microscopy. The crystal edges were sharp whereas their surfaces were very rough. Energy dispersive spectroscopy showed that the crystals contained only the elements calcium, carbon, and oxygen. Selected area electron diffraction and near infrared Raman spectroscopy established that the crystals were calcite. With the exception of the otoconia structure of the inner ear, this is the only known nonpathological occurrence of calcite in the human body. The calcite microcrystals are probably responsible for the previously observed second harmonic generation in pineal tissue sections. The complex texture structure of the microcrystals may lead to crystallographic symmetry breaking and possible piezoelectricity, as is the case with otoconia. It is believed that the presence of two different crystalline compounds in the pineal gland is biologically significant, suggesting two entirely different mechanisms of formation and biological functions. Studies directed toward the elucidation of the formation and functions, and possible nonthermal interaction with external electromagnetic fields are currently in progress. Bioelectromagnetics 23:488,495, 2002. © 2002 Wiley-Liss, Inc. [source] Cyclometalated IrIII Complexes with Substituted 1,10-Phenanthrolines: A New Class of Efficient Cationic Organometallic Second-Order NLO ChromophoresCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2010Adriana Valore Dr. Abstract Cyclometalated cationic IrIII complexes with substituted 1,10-phenanthrolines (1,10-phen), such as [Ir(ppy)2(5-R-1,10-phen)]Y (ppy=cyclometalated 2-phenylpyridine; R=NO2, H, Me, NMe2; Y,=PF6,, C12H25SO3,, I,) and [Ir(ppy)2(4-R,7-R-1,10-phen)]Y (R=Me, Ph) are characterized by a significant second-order optical non linearity (measured by the electrical field induced second harmonic generation (EFISH) technique). This nonlinearity is controlled by MLCT processes from the cyclometalated IrIII, acting as a donor push system, to ,* orbitals of the phenanthroline, acting as an acceptor pull system. Substitution of cyclometalated 2-phenylpyridine by the more , delocalized 2-phenylquinoline (pq) or benzo[h]quinoline (bzq) or by the sulfur-containing 4,5-diphenyl-2-methyl-thiazole (dpmf) does not significantly affect the ,, absolute value, which instead is affected by the nature of the R substituents on the phenanthroline, the higher value being associated with the electron-withdrawing NO2 group. By using a combined experimental (the EFISH technique and 1H and 19F PGSE NMR spectroscopy) and theoretical (DFT, time-dependent-DFT (TDDFT), sum over states (SOS) approach) investigation, evidence is obtained that ion pairing, which is controlled by the nature of the counterion and by the concentration, may significantly affect the ,, values of these cationic NLO chromophores. In CH2Cl2, concentration-dependent high absolute values of ,, are obtained for [Ir(ppy)2(5-NO2 -1,10-phen)]Y if Y is a weakly interacting anion, such as PF6,, whereas with a counterion, such as C12H25SO3, or I,, which form tight ion-pairs, the absolute value of ,, is lower and quite independent of the concentration. This ,, trend is partially due to the perturbation of the counterion on the LUMO ,* levels of the phenanthroline. The correlation between the ,, value and dilution shows that the effect of concentration is a factor that must be taken into careful consideration. [source] Synthesis of Novel Chiral and Acentric Coordination Polymers by the Reaction of Zinc or Cadmium Salts with Racemic 3-Pyridyl-3-aminopropionic AcidCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2004Zhi-Rong Qu Abstract Under hydrothermal (solvothermal) reaction conditions chiral compounds 1, 2, and 3 and one acentric compound 4 were obtained by the reaction of Zn2+ or Cd2+ with racemic 3-(3-pyridyl)-3-aminopropionic acid (rac -HPAPA). Compounds 1 and 2 crystallized in chiral space group P212121. At 105,°C, racemic 3-pyridyl-3-aminopropionic acid (rac -HPAPA) reacted with Zn(ClO4)2,6,H2O and dehydrogenated in situ to form the first chiral coordination polymer [Zn{(E)-3-C5H4NC(NH2)CHCOO}]ClO4 (1) with a ,-dehydroamino acid. Beyond 120,°C, the reaction of rac -HPAPA with Zn(ClO4)2,6,H2O deaminates in situ to form chiral coordination polymer [Zn{(E)-3-C5H4NCHCHCOO}(OH)] (2). At relatively low temperatures (70,°C), the solvothermal reaction of Zn(NO3)2,6,H2O with rac -HPAPA in methanol does not lead to any change in the ligand and results in the formation of a chiral (P212121) coordination polymer [Zn(papa)(NO3)] (3). The same reaction of Cd(ClO4)2,6,H2O with HPAPA also does not lead to any change in ligand and results in the formation of noncentric (Cc) coordination polymer [Cd(papa)(Hpapa)]ClO4,H2O (4). The network topology of both 1 and 3 is 10,3a, while 2 has a diamondoid-like (KDP-like, KDP=potassium dideuterophosphate) network. Particularly interesting from a topological perspective is that 4 has an unprecedented three-dimensional network. Compounds 1, 2, 3, and 4 are all second harmonic generation (SHG) active with 1 exhibiting the strongest response, while only 4 also displays good ferroelectric properties. [source] The Role of Ion Pairs in the Second-Order NLO Response of 4-X-1-Methylpiridinium Salts,CHEMPHYSCHEM, Issue 2 2010Francesca Tessore Dr. Abstract A series of 4-X-1-methylpyridinium cationic nonlinear optical (NLO) chromophores (X=(E)-CHCHC6H5; (E)-CHCHC6H4 -4,-C(CH3)3; (E)-CHCHC6H4 -4,-N(CH3)2; (E)-CHCHC6H4 -4,-N(C4H9)2; (E,E)-(CHCH)2C6H4 -4,-N(CH3)2) with various organic (CF3SO3,, p -CH3C6H4SO3,), inorganic (I,, ClO4,, SCN,, [Hg2I6]2,) and organometallic (cis -[Ir(CO)2I2],) counter anions are studied with the aim of investigating the role of ion pairing and of ionic dissociation or aggregation of ion pairs in controlling their second-order NLO response in anhydrous chloroform solution. The combined use of electronic absorption spectra, conductimetric measurements and pulsed field gradient spin echo (PGSE) NMR experiments show that the second-order NLO response, investigated by the electric-field-induced second harmonic generation (EFISH) technique, of the salts of the cationic NLO chromophores strongly depends upon the nature of the counter anion and concentration. The ion pairs are the major species at concentration around 10,3,M, and their dipole moments were determined. Generally, below 5×10,4,M, ion pairs start to dissociate into ions with parallel increase of the second-order NLO response, due to the increased concentration of purely cationic NLO chromophores with improved NLO response. At concentration higher than 10,3,M, some multipolar aggregates, probably of H type, are formed, with parallel slight decrease of the second-order NLO response. Ion pairing is dependent upon the nature of the counter anion and on the electronic structure of the cationic NLO chromophore. It is very strong for the thiocyanate anion in particular and, albeit to a lesser extent, for the sulfonated anions. The latter show increased tendency to self-aggregate. [source] Laser-induced crystal growth of nonlinear optical Ba3Ti3O6(BO3)2 on glass surfaceCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2008T. Oikawa Abstract Nonlinear optical Ba3Ti3O6(BO3)2 crystals were patterned on the surface of CuO (1 mol%)-doped 40BaO-40TiO2 -20B2O3 glass by irradiations of continuous-wave Nd:YAG (wavelength: ,=1064 nm) and Yb:YVO4 (,=1080 nm) lasers. Laser energies absorbed by Cu2+ ions were transferred to the lattice system through a nonradiative relaxation process, consequently heating the glass and inducing local crystallizations. For the lines patterned by Yb:YVO4 laser irradiations with a power of 1 W and a scanning speed of 20 ,m/s, a c -axis orientation of Ba3Ti3O6(BO3)2 crystals along the laser scanning direction is proposed from measurements of X-ray diffraction analyses, polarized optical photographs, polarized micro-Raman scattering spectra, and azimuthal dependence of second harmonic generations. The laser-induced crystallization technique is found to be applied successfully for the spatially selective patterning of nonlinear optical Ba3Ti3O6(BO3)2 crystals in glass. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||||||||||||||