Second Harmonic Generating Research Articles

Sr2[C6H3(CO2)3(NO3)]·DMF: One-Dimensional Nano-Channel in a New Non-Centrosymmetric Strontium–Organic Framework with High Thermal Stability

A new non-centrosymmetric strontium–organic framework material (CAUMOF-8) with one-dimensional nanochannels has been synthesized under solvothermal conditions. CAUMOF-8 exhibits a helical channel structure consisting of strontium oxide polyhedra and a 1,3,5-benzenetricarboxylate linker. The channels run along the c-axis and are approximately 12 Å in diameter. The amount of void space for the material can be calculated to be ca. 47% from the single-crystal structure. The structure exhibits a very high thermal stability up to 520 °C. Powder second-harmonic generating (SHG) measurements on CAUMOF-8 revealed SHG efficiency of 20 times that of α-SiO2 and the material is phase-matchable (Type 1).

Second harmonic generating (SHG) nanoprobes for in vivo imaging

Fluorescence microscopy has profoundly changed cell and molecular biology studies by permitting tagged gene products to be followed as they function and interact. The ability of a fluorescent dye to absorb and emit light of different wavelengths allows it to generate startling contrast that, in the best cases, can permit single molecule detection and tracking. However, in many experimental settings, fluorescent probes fall short of their potential due to dye bleaching, dye signal saturation, and tissue autofluorescence. Here, we demonstrate that second harmonic generating (SHG) nanoprobes can be used for in vivo imaging, circumventing many of the limitations of classical fluorescence probes. Under intense illumination, such as at the focus of a laser-scanning microscope, these SHG nanocrystals convert two photons into one photon of half the wavelength; thus, when imaged by conventional two-photon microscopy, SHG nanoprobes appear to generate a signal with an inverse Stokes shift like a fluorescent dye, but with a narrower emission. Unlike commonly used fluorescent probes, SHG nanoprobes neither bleach nor blink, and the signal they generate does not saturate with increasing illumination intensity. The resulting contrast and detectability of SHG nanoprobes provide unique advantages for molecular imaging of living cells and tissues.

Polar Hexagonal Tungsten Oxide (HTO) Materials: (1) Synthesis, Characterization, Functional Properties, and Structure−Property Relationships in A2(MoO3)3(SeO3) (A = Rb+ and Tl+) and (2) Classification, Structural Distortions, and Second-Harmonic Generating Properties of Known Polar HTOs

Two new polar noncentrosymmetric (NCS) oxides, Rb2(MoO3)3(SeO3) and Tl2(MoO3)3(SeO3), have been synthesized and characterized. The materials exhibit the layered hexagonal tungsten oxide (HTO) structural topology—Class 2, i.e., the MoO6 layers are “capped” on one side by the SeO3 polyhedra. The Rb+ and Tl+ cations are found between the layers. The Mo6+ and Se4+ cations are present in asymmetric coordination environments that are attributable to second-order Jahn−Teller (SOJT) effects. In addition to structural characterization, the materials were characterized by second-harmonic generation (SHG), piezoelectric, and polarization measurements. SHG measurements using 1064-nm radiation revealed doubling efficiencies of 300 and 400 × α-SiO2 for the Rb- and Tl-phases, respectively. Piezoelectric experiments revealed d33 values of ∼9−13 pm/V. Polarization measurements indicate that the materials are not ferroelectric, i.e., the polarization is not “switchable”. The materials are pyroelectric, with total pyroelect...

Growth and optical characteristics of coumarin 6 doped potassium hydrogen phthalate (KAP) crystals

Single-crystals of potassium hydrogen phthalate (KAP) doped with coumarin 6 (C6) were grown by solution evaporation technique. Powder X-ray diffraction, optical transmission and luminescence measurements were performed. The structure and morphology of the KAP crystals are not changed with the incorporation of the dye. Transparency of the dye-doped crystals is suited for non-linear optical (NLO) applications and UV cut-off is not changed when compared with the pure KAP crystals. The dye-doped crystals present an absorption band at 350 nm while the growth solution exhibits a peak at 400 nm. The doped crystals have a strong emission band at 450 nm that is excited at 350 nm and the second harmonic generating (SHG) properties are demonstrated using luminescence measurements.

Structures and Non-linear Optical Properties of Multi-Sulfur π-Conjugated Compounds 4,5-Vinylenedithio-1,3-dithiole-2-thione (C5H2S5) and 4,5-Vinylenedithio-1,3-dithiole-2-one (C5H2OS4)

Both the title multi-sulfur molecules C5H2S5 (1) and C5H2OS4 (2) have a chair conformation, while molecule 1 has a higher degree of π-conjugation. Both the crystals are characterized by short S···S intermolecular contacts and by face-to-face column-like packing style, but crystal 1 has been more stabilized which may be the result of its stronger π–π intermolecular interactions. Compound 1 crystallizes in non-centrosymmetric polar space group Pmn21 with a = 10.6826(17), b = 9.3633(11), c = 4.0764(6) A, V = 407.74(10) A3, and Z = 2. The molecular dipole moment of 1 is ±62.5(1)° away from the macro-polarization direction along the c-axis. Consequently, the crystalline powder of crystal 1 exhibit a second harmonic generating (SHG) intensity 0.5 time strong as that of urea standard powder crystals when irradiated by a 1,080 nm of Nd:YAP laser beam. Compound 2 shows no SHG effect because it crystallizes in centrosymmtric space group Pbca with a = 11.4208(8), b = 7.8843(9), c = 33.587(3) A, V = 3024.3(5) A3, and Z = 16. Structures and Non-linear Optical Properties of Multi-Sulfur π-Conjugated Compounds 4,5-Vinylenedithio-1,3-dithiole-2-thione (C5H2S5) and 4,5-Vinylenedithio-1,3-dithiole-2-one (C5H2OS4) Gang Xue, Qi Fang,* Wen-Tao Yu, Xia Chen, and Hong Lei Compound C5H2S5 crystallizes in the polar space group Pmn21 and its crystalline powder exhibits a second harmonic generating (SHG) intensity 0.5 times that of urea standard (1080 nm → 540 nm), while the similar compound C5H2OS4 has no SHG effect because of its centrosymmetric space group Pbca.

Two New Noncentrosymmetric Polar Oxides: Synthesis, Characterization, Second-Harmonic Generating, and Pyroelectric Measurements on TlSeVO5 and TlTeVO5

Two new noncentrosymmetric (NCS) polar quaternary oxides, TlMVO5 (M = Se4+ or Te4+), have been synthesized by hydrothermal techniques using Tl2CO3, SeO2 (TeO2), and V2O5 as reagents. The structures were determined by single-crystal X-ray diffraction (TlSeVO5, orthorhombic, space group Pna21 (No. 33) with a = 7.1639(15) Å, b = 8.6630(19) Å, c = 7.8946(17) Å, V = 489.95(18) Å3, and Z = 4; TlTeVO5, orthorhombic, space group Pna21 (No. 33) with a = 7.319(3) Å, b = 8.749(4) Å, c = 7.868(3) Å, V = 503.8(4) Å3, Z = 4). The materials exhibit NCS and polar three-dimensional structures consisting of chains of corner shared VO6 octahedra connected by SeO3 (TeO4) and TlO8 polyhedra. The V5+, Se4+ (Te4+), and Tl+ cations are in asymmetric coordination environments attributable to second-order Jahn−Teller (SOJT) effects. The V5+ cations undergo intra-octahedral distortions toward an edge (local C2 direction), whereas the Se4+ (Te4+) and Tl+ cations are in distorted coordination environments attributable to their lone-pair. As the materials are NCS and polar, second-harmonic generating (SHG), ferroelectric, and pyroelectric measurements were performed. The SHG measurements, using 1064 nm radiation, revealed doubling efficiencies of ∼40 × α-SiO2 for both TlSeVO5 and TlTeVO5. Ferroelectric measurements indicated the materials are not “switchable”; that is, the local dipole moment cannot be reversed in the presence of an external electric field. Pyroelectric measurements revealed a total pyroelectric coefficient, p, of −2.9 and −1.9 μC/m2·K, for TlSeVO5 and TlTeVO5, respectively. Infrared, Raman, UV−vis diffuse reflectance spectroscopy, and thermal analyses are also presented.

SbSbxM1−xO4 (M=NbV or TaV): Solid Solution Behavior and Second-Harmonic Generating Properties

The solid solution behavior and second-harmonic generating (SHG) properties of SbSbxM1−xO4 (M=NbV or TaV) (x=0.0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1.0) have been investigated by powder X-ray diffraction and nonlinear optical (NLO) measurements. Both SbNbO4 and SbTaO4 form solid solutions with α-Sb2O4. All the materials crystallize in the non-centrosymmetric space group Pna21, with SbIIIO4E polyhedra linked to MVO6 (MV=SbV, NbV, or TaV) octahedra. SHG data is presented for the solid solutions and α-Sb2O4, SbNbO4, and SbTaO4. With respect to the SbSbxM1−xO4 phases, NLO measurements indicate a substantial decrease in SHG efficiency for x≥0.6. This decrease is attributable to the “nonpolar” nature of the SbVO6 octahedra compared with the polar nature of NbVO6 or TaVO6.

Synthesis and Characterization of Te2SeO7: A Powder Second-Harmonic-Generating Study of TeO2, Te2SeO7, Te2O5, and TeSeO4

The synthesis and characterization of a noncentrosymmetric tellurium selenate, Te2SeO7, is reported. In addition, the powder second-harmonic-generating (SHG) properties of TeO2, Te2SeO7, Te2O5, and TeSeO4 have been measured, using 1064 nm radiation. Through the powder SHG experiments, we are able to determine that TeO2 is not phase-matchable, whereas Te2SeO7, Te2O5, and TeSeO4 are phase-matchable. Also, TeO2, Te2SeO7, Te2O5, and TeSeO4 have SHG efficiencies of 5, 200, 400, and 400 times SiO2, respectively. The relative SHG efficiencies may be understood by examining the structure of each material. Through the powder SHG measurements, we estimate the average nonlinear optical bond susceptibility, 〈d2ωijk〉, for each material.

Epitaxy of K3Li2Nb5O15 (KLN) films on KLN fiber crystal substrates

Potentially useful second harmonic generating (SHG) K3Li2Nb5O15 (KLN) films have been prepared by liquid phase epitaxy. Ta-deficient and Ta-substituted KLN fiber crystals produced by micro-pulling down (μ-PD) technique were used for the first time as a substrate. The films were grown from the V2O5 based fluxes by conventional dipping technique without rotation. The film composition was measured by electron probe micro-analysis (EPMA). The incorporation of V5+ cations into the KLN structure is low.

Homoclinic orbits and chaos in a second-harmonic generating optical cavity

We present two large families of Šilnikov-type homoclinic orbits in a two-mode model that describes second-harmonic generation in a passive optical cavity. These families of homoclinic orbits give rise to chaotic dynamics in the model.

Gigantic optical non-linearities from nanoparticle-enhanced molecular probes with potential for selectively imaging the structure and physiology of nanometric regions in cellular systems

The requirement to functionally probe biological structures, with ever increasing selectivity and three-dimensional resolution is a frontier area in microscopy. Non-linear optics has a unique potential in this regard with numerous studies focused on the potential of three-dimensional imaging with super-resolution. In this paper we demonstrate that non-linear optical phenomena, such as second harmonic (SH) generation, which is very sensitive to the membrane potential, can be locally enhanced by complexing or approaching a SH generating molecular probe to a nanoantenna of a silver or gold nanoparticle. This gives complexes with gigantic optical non-linearities. These contrast enhancing non-linear optical complexes have the potential to be directed selectively to specific nanometric regions in cells in order to report on alterations on the structure and the function in such regions while overcoming the inherent inefficiency of non-linear optical interactions.

Crystal growth, frequency doubling, and infrared laser performance of Yb/sup 3+/:BaCaBO/sub 3/F

Yb:BaCaBO/sub 3/F(Yb:BCBF) has been investigated as a new laser crystal with potential for self-frequency doubling, Yb/sup 3+/ in BCBF exhibits a maximum absorption cross section at 912 nm of 1.1/spl times/10/sup -20/ cm/sup 2/ with a bandwidth (FWHM) of 19 nm. The maximum emission cross section at 1034 nm is 1.3/spl times/10/sup -20/ cm/sup 2/ with a transition bandwidth of 24 nm. The measured emission lifetime of Yb/sup 3+/ is 1.17 ms. An Yb:BCBF laser has been demonstrated with a Ti:sapphire pump source, and a measured slope efficiency of 38% has been obtained for the fundamental laser output. Single crystal powders of BCBF have been compared with KD/sup +/P for a relative measure of the second-harmonic generating potential, yielding d/sub eff/(BCBF)/spl sim/0.26 pm/V. The phasematching angle has been estimated from the refractive index data for type I second-harmonic generation of 0.517 /spl mu/m light; the predicted angle is 37/spl deg/ from the c-axis. The growth, spectroscopy, laser performance, and linear and nonlinear optical properties of Yb:BCBF are reported.

The structural pressure dependence of potassium titanyl phosphate (KTP) to 8 GPa

The crystal structure of (KTP) has been determined as a function of pressure to 8 GPa at ambient temperature, using single-crystal x-ray diffraction techniques. The first-order isosymmetric phase transition, at 5.8 GPa, appears to have a strong effect on the compression mechanism of the structure: in the low-pressure phase the structure compresses by polyhedral tilting within the cross-linking chains while in the high-pressure phase relative translations and rotations of the chains themselves account for a significant proportion of the unit-cell volume reduction both at the transition and on further pressure increase. The distortion of the framework at the phase transition is accompanied by relatively large displacements of the potassium atoms to positions more closely related to the Pnan symmetry of the high-temperature phase. A comparison of the pressure-induced changes of the highly distorted octahedra with recent high-pressure optical measurements indicates that neither the lengths nor the orientations of the Ti - O bonds correlate, at least directly, with the observed variation of the second-harmonic-generating (SHG) power of the crystal. This strongly suggests that other regions of the structure may be important for the SHG properties. .

Second Harmonic Generation in Carbon Dioxide Processed Thin Polymer Films

Polymer films were swelled with carbon dioxide (CO2), allowing the alignment of second harmonic generating (SHG) chromophores with an electric field at ambient temperatures. SHG decay provided info...

Transverse diffusion of minority carriers confined near the GaAs surface plane.

Spatially separated second-harmonic generating and photocarrier exciting light beams were employed to study transverse diffusion of carriers confined near GaAs(001) surfaces. The measurements utilize the intrinsic sensitivity of second-harmonic generation to surface charge density in order to probe these processes. Carrier transport was found to be diffusive with small effective diffusion coefficients compared to those of carriers in the bulk. Several models are considered to explain these results.

In situ poling and polymerization of multifunctional monomers for second harmonic generation

AbstractA novel method for the synthesis of second harmonic generating (SHG) materials is proposed and tested in which liquid, multifunctional monomers with dissolved dopants are poled and polymerized simultaneously. Instead of requiring multiple steps and hours or days to synthesize SHG materials, this technique is able to produce doped guest/host systems in a single step process which takes two minutes or less. In addition, the polymer that is produced is highly crosslinked and provides good thermal and temporal stability of the SHG. To increase the stability of the SHG signal the dopant can be attached to the crosslinked network further decreasing the mobility. Advantages of this process include its simplicity, speed, stability, and the ability to make SHG materials of any thickness by successively polymerizing layers. This work presents a detailed description of the new procedure as well as results for the effect of dopant concentration, the magnitude of the SHG, and the structure of the crosslinked polymer that serves as the dopant host. Also, a method of synthesizing functionalized Disperse Red 1 that can be incorporated as a side chain is presented. Results are presented for the order parameter and SHG stability at room temperature and 100°C.

Second-harmonic generation in poly(α-amino acid) and poly(isocyanate) films

Films of poly(γ-benzyl- l-glutamate) (PBLG) and poly(hexylisocyanate) (PHIC) were cast from solution whilst under electric fields generated between parallel strip electrodes placed at the surface. Because of their chain rigidity and large macromolecular dipole moments, this procedure induces some parallel chain alignments in the field direction, even if the fields are low (⩽ 300 V mm −1). The field induces a degree of non-centrosymmetric order in the films which is retained after the field is removed. In these ordered states such films were found to have second-harmonic generating (SHG) ability under 1.06 μm irradiation and this ability did not age over a period of 6 months. The SHG activity varied with the angle of polarized radiation relative to the poling direction, showing a single maximum and minimum for PHIC (uniaxial symmetry) and double maxima and minima for PBLG (biaxial symmetry) over π radians. Optical microscopy of the PBLG films formed under electric fields showed regions of nematic as well as cholesteric order.

Analysis of a first-order reflection grating with second-harmonic generation

The operation of a first-order reflection grating, superposed on a dielectric waveguide with a second-order nonlinearity, is analyzed. Such a grating termination to a second-harmonic generating waveguide is shown to operate as an efficient wavelength-selective reflector(ω)/radiator(2ω) for the two respective harmonic input guided waves, in particular in a second-harmonic (SH) resonator. It is shown that radiation efficiency for the input SH wave depends on the phase difference between the two input waves and on the ratio between the input SH power and the SH power generated inside the grating. In certain cases the input SH wave experiences gain as it is radiated, with the fundamental input wave acting as a pump.