Second Harmonic Generation Properties Research Articles

KBe2BO3F2晶体的非共线倍频特性数值分析

KBe2BO3F2晶体的非共线倍频特性数值分析

Size effect on the SHG properties of Cu-doped CdI 2 nanocrystals

Because the optically induced second harmonic generation (SHG) is prevented by symmetry in a centrosymmetric material, one needs to form noncentrosymmetric processes in order to observe the SHG. However, one of the efficient ways to enhance the noncentrosymmetricity of a material is to dope it with an appropriate impurity and amount. We grow Cu-doped CdI 2 layered nanocrystal structures from the mixture of CdI 2 and CuI using the standard Bridgman–Stockbarger method and investigate the nano-confined effects by studying the second-order optical effect via the measurements of SHG. The second-order susceptibility for the nanocrystals is calculated and the values at liquid helium temperature range from 0.38 to 0.83 pm V −1 for the thicknesses of 10–0.8 nm respectively. The size dependence demonstrates the nano-sized quantum-confined effect with a clear increase in the SHG with decreasing the thickness of the nanocrystal or crystal temperature. Since the local electron–phonon anharmonicity is described by third-order rank tensors in disordered systems, the SHG is very similar to that one introduced for the third-order optical susceptibility. It has been confirmed by observing the large photoluminescent yield of the pure crystals. The Raman scattering spectra taken for thin nanocrystals confirm the phonon modes originating from interlayer phonons crucially responsible for the observed effects. The obtained results show that the Cu-doped CdI 2 layered nanocrystals are promising materials for applications in optoelectronic nano-devices.

Growth, Structure, and Optical Properties of a Congruent Melting Oxyborate, Bi2ZnOB2O6

A single crystal of Bi2ZnOB2O6 has been grown with sizes up to 18 × 13 × 6 mm3 by the top-seeded growth method for the first time with high quality. It crystallizes in the orthorhombic system, space group Pba2 with unit-cell parameters a = 10.8200(7) Å, b = 11.0014(7) Å, c = 4.8896(3) Å, Z = 4, V = 582.03(6) Å3. Bi2ZnOB2O6 has a three-dimensional network consisting of ZnB2O76- layers alternating with six-coordinated Bi3+ cations along the c axis. Transmission spectrum of Bi2ZnOB2O6 crystal was reported. The refractive indices of the crystal were measured by the minimum deviation technique and fitted to the Sellmeier equations. The powder second-harmonic generation (SHG) properties measured by the Kurtz−Perry method indicate that Bi2ZnOB2O6 is phase-matchable.

Semiorganic Nonlinear Optical Material: Preparation and Properties of (NH4)·Sr[l-(+)-C4H2O6·B(OH)2]·4H2O

The synthesis, crystal structure, and characterization of the noncentrosymmetric semiorganic material (NH(4)).Sr[l-(+)-C(4)H(2)O(6).B(OH)(2)].4H(2)O were reported. Crystals were synthesized through slow evaporation at room temperature, utilizing SrCl(2).6H(2)O, C(4)H(4)O(6), H(3)BO(3), and NH(3).H(2)O as reagents, and its structure was determined by single-crystal X-ray diffraction. It crystallizes in the triclinic space group P1 (No. 1) with a = 6.4633(10) A, b = 7.0452(13) A, c = 7.0745(12) A, alpha = 85.351(5) degrees , beta = 77.678(5) degrees , gamma = 73.276(4) degrees , and Z = 1. It exhibits a two-dimensional layered structure along the c axis, consisting of SrO(9) polyhedra, BO(4) tetrahedra, tartrate molecules, NH(4)(+) cations, and H(2)O molecules. IR spectroscopy, UV-vis diffuse-reflectance spectroscopy, thermal analysis, and second-harmonic generation (SHG) were also performed on the reported material. Nonlinear optical measurements, using 1064 nm radiation, indicate that the material has SHG properties, with an efficiency of approximately 1.5 times that of KH(2)PO(4).

Bottom-up approach to nonlinear optical imaging of biomaterials

Biological tissues are complex systems. Conventional microscopy, ultimately limited to a spatial resolution of roughly half the wavelength of light, is often unable to see molecular details unless sophisticated and invasive methods are employed. However, recent advances in nonlinear optical-imaging techniques for biological tissues have resulted in both higher spatial resolution and better tissue contrast than achieved before.1 As a result, a great deal of focus has been placed on engineering nonlinear optical probes for use with two-photon excitedfluorescence and second-harmonic-generation (SHG) imaging. Both employ femtosecond-laser microscopy to measure nonlinear optical responses. In SHG, two photons at a fundamental frequency are converted into one at once or twice the harmonic frequency. In addition to the numerous organic and inorganic optical probes that have been developed for labeling tissues and cell membranes, certain cellular components, such as collagen, have intrinsic SHG properties.2 This makes SHG a favourable method for noninvasive imaging of large structures and cellular processes. However, it still lacks resolution at the molecular level. In addition, for smaller components the relationship between the intensity and polarization state of the nonlinear optical response and the molecule’s conformation remains elusive. Here, we provide preliminary insights into this dependence. In addressing this problem, the focus is usually placed on the imaging potential of the techniques. Very few studies have tackled the problem in a bottom-up approach, starting from the elementary bricks of the proteins—the individual amino acids— and working up to the protein itself. The nonlinear optical properties of these molecules can be observed using hyper-Rayleigh Figure 1. Quadratic hyperpolarizability of tryptophan (W)-rich peptides as a function of the number of these amino acids. Dots: Experimental data. Empty circles and squares: coherent and incoherent models, respectively.

Selective Detection of Protein Crystals by Second Harmonic Microscopy

The unique symmetry properties of second harmonic generation (SHG) microscopy enabled sensitive and selective imaging of protein microcrystals with negligible contributions from solvated proteins or amorphous protein aggregates. In studies of microcrystallites of green fluorescent protein (GFP) prepared in 500 pL droplets, the SHG intensities rivaled those of fluorescence, but with superb selectivity for crystalline regions. GFP in amorphous aggregates and in solution produced substantial background fluorescence, but no detectable SHG. The ratio of the forward-to-backward detected SHG provides a measure of the particle size, suggesting detection limits down to crystallites 100 nm in diameter under low magnification (10x). In addition to being sensitive and highly selective, second-order nonlinear optical imaging of chiral crystals (SONICC) is directly compatibility with virtually all common protein crystallization platforms.

Polar Hexagonal Tungsten Bronze-Type Oxides: KNbW2O9, RbNbW2O9, and KTaW2O9

The synthesis, crystal structures, second-harmonic generation (SHG), piezoelectric, pyroelectric, and ferroelectric properties of three polar noncentrosymmetric (NCS) hexagonal tungsten bronze-type oxides are reported. The materials KNbW 2O 9, RbNbW 2O 9, and KTaW 2O 9 were synthesized by standard solid-state techniques and structurally characterized by laboratory powder X-ray diffraction. The compounds are isostructural, crystallizing in the polar NCS space group Cmm2. The materials exhibit a corner-shared MO 6 (M = Nb (5+)/W (6+) or Ta (5+)/W (6+)) octahedral framework, with K (+) or Rb (+) occupying the "hexagonal" tunnels. The d (0) transition metals, Nb (5+), Ta (5+), and W (6+), are displaced from the center of their oxide octahedra attributable to second-order Jahn-Teller effects. SHG measurements using 1064 nm radiation revealed frequency-doubling efficiencies ranging from 180 to 220 x alpha-SiO 2. Converse piezoelectric measurements resulted in d 33 values ranging from 10 to 41 pm V (-1). The total pyroelectric coefficient, p, at 50 degrees C ranged from -6.5 to -34.5 muC K (-1) m (-2). The reported materials are also ferroelectric, as demonstrated by hysteresis loops (polarization vs electric field). Spontaneous polarization values, P s, ranging from 2.1 to 8.4 muC cm (-2) were measured. The magnitudes of the SHG efficiency, piezoelectric response, pyroelectric coefficient, and ferroelectric polarization are strongly dependent on the out-of-center distortion of the d (0) transition metals. Structure-property relationships are discussed and explored. Crystal data: KNbW 2O 9, orthorhombic, space group Cmm2 (No. 35), a = 21.9554(2) A, b = 12.60725(15) A, c = 3.87748(3) A, V = 1073.273(13) A (3), and Z = 6; RbNbW 2O 9, orthorhombic, space group Cmm2 (No. 35), a = 22.00985(12) A, b = 12.66916(7) A, c = 3.8989(2) A, V = 1086.182(10) A (3), and Z = 6; KTaW 2O 9, orthorhombic, space group Cmm2 (No. 35), a = 22.0025(2) A, b = 12.68532(14) A, c = 3.84456(4) A, V = 1073.05(2) A (3), and Z = 6.

Lead–strontium borate halides with hilgardite-type structure and their SHG properties

Lead-containing members of the hilgardite family of borate halides, M 2B 5O 9 X ( M=Ca, Sr, Ba, Pb; X=Cl, Br) exhibit an abnormally large nonlinear optical response. In order to establish any underlying crystal-chemical rationale for this we have carried out detailed crystallographic characterisations of the representative members of this series, Sr 2B 5O 9Cl and Pb 2B 5O 9Cl, using powder neutron diffraction. Both adopt the orthorhombic hilgardite structure type, in space group Pnn2. The full solid solution range Pb 2− x Sr x B 5O 9Cl has also been prepared, and studied by X-ray Rietveld and second harmonic generation (SHG) measurements. The SHG response shows a linear decrease with increasing x, whereas the unit cell shows an increasing orthorhombic distortion. However, the crystallographic results suggest no significant or systematic changes in the nature of the borate sublattice between Sr 2B 5O 9Cl and Pb 2B 5O 9Cl. We conclude that the enhanced SHG response in Pb-containing hilgardites is due predominantly to the presence of the polarizable nature of Pb 2+, in particular the presence of a stereochemically active lone pair.

Preparation and Second-Harmonic Generation Properties of a Self-Assembled Multilayer Film Based on Nanoporous Isopolyoxomolybdate and Bipolar Hemicyanine

An electrostatic self-assembled multilayer film has successfully been prepared by alternating adsorption of a wheel-shaped nanoporous isopolyoxomolybdate and a bipolar hemicyanine derivative, as monitored by absorption spectroscopy. The square roots of second-harmonic intensities of the film exhibit quadratic dependence on film thickness up to 10 layers. The average titled angle of the nonlinear optical chromophores to the substrate normal is derived to be 34 degrees by polarized second-harmonic generation measurements.

Preparation and Second-Harmonic Generation Properties of a Self-Assembled Multilayer Film Based on Nanoporous Isopolyoxomolybdate and Bipolar Hemicyanine

The effects of pH value, surfactant, and electrolyte concentration on zeta potential, particle agglomeration, and thermal conductivity of nanofluids are investigated. The zeta potential of TiO2 (15 nm) nanoparticles in deionized water of different pH values was measured and the iso-electric point was found to be between 4.9 and 5.2. Addition of surfactant in the base fluid increases the zeta potential and thus increases the effective thermal conductivity of nanofluids. The results show that the higher the electrolyte concentration, the smaller the particle zeta potential, which results in increased agglomeration of particles. The enhanced thermal conductivity of TiO2/deionized water-based nanofluids was found to decrease with increasing pH value or electrolyte concentration. At 0.2 volume percentage of TiO2 nanoparticles, the decrease of thermal conductivity of nanofluids was within 2% when the pH value or electrolyte concentration was increased from 3.4 to 9 or 0.01 mM to 10 mM, respectively. The hydrodynamic diameter of agglomerated nanoparticles in base fluid was also measured and found to increase with increasing electrolyte concentration.

Synthesis, Characterization, Langmuir−Blodgett Film-Forming Property, and Second-Order Nonlinear Optical Study of Rhenium(I) and Ruthenium(II) Diimine Complexes

A series of rhenium(I) and ruthenium(II) complexes of general formulas fac-[Re(CO)3ClL] and [Ru(bpy)2L](PF6)2 (L = N-(4-biphenyl)pyridine-2-carbaldimine (L1), N-[4-(4‘-octadecyloxy)biphenyl]pyridine-2-carbaldimine (L2), (5-octadecyloxy)-2-pyridine-N-(4-biphenyl)carbaldimine (L3), and (5-octadecyloxy)-2-pyridine-N-[4-(4‘-octadecyloxy)biphenyl]carbaldimine (L4)) were synthesized and characterized, and their photophysical properties were also studied. The X-ray crystal structures of fac-[Re(CO)3ClL1] and [Ru(bpy)2L1](PF6)2 have been determined. These complexes were capable of forming stable Langmuir−Blodgett (LB) films, as revealed by the study of their surface pressure−area (π−A) isotherms, and their second-harmonic generation (SHG) properties were also investigated.

The Role of Backscattering in SHG Tissue Imaging

We investigate the properties of second-harmonic generation (SHG) tissue imaging for the functional biological unit fascia, skeletal muscle, and tendon. Fascia and Achilles tendon primarily consist of similar collagen type I arrays that can be imaged using SHG microscopy. For muscle, it is the myosin molecules represented within the A bands. For fascia and tendon tissue samples, we observe, in addition to a stronger signal in forward images, vastly different features for the backward versus the forward images. In vivo as well as intact ex vivo thick tissue imaging requires backward detection. The obtained image is a result of the direct backward components plus a certain fraction of the forward components that are redirected (backscattered) toward the objective as they propagate within the tissue block. As the forward and the backward images are significantly different from each other for the imaged collagen type I tissue, it is crucial to determine the fraction of the forward signal that contributes to the overall backward signal. For intact ex vivo SHG imaging of Achilles tendon, we observe a significant contribution of forward features in the resulting image. For fascia, the connective tissue immediately surrounding muscle, we only observe backward features, due to low backscattering in muscle.

Properties of second harmonic generation in nonlinear optical crystals CsLiB 6O 10 and K 2Al 2B 2O 7

The phase-matching for nonlinear optical crystal, the nonlinear phase matching angle, effective nonlinear coefficient, walk-off angles, permitted angle, and permitted wavelength are obtained in type-I and type-II phase matching in ultraviolet (UV) nonlinear optical crystals CsLiB 6O 10 (CLBO) and K 2Al 2B 2O 7 (KABO) by detailed theoretical simulation. Through analysis and comparison, the phase matching characteristics of the second harmonic generation in the crystals are discussed when the wavelengths of the basic frequency lights turn continually.

Metal-controlled assembly tuning the topology and dimensionality of coordination polymers of Ag(I), Cd(II) and Zn(II) with the flexible 2-(1 H-imidazole-1-yl)acetic acid (Hima)

Three new, inorganic–organic coordination polymers based on a versatile linking unit 2-(1 H-imidazole-1-yl)acetate (ima) and Ag I, Cd II and Zn II ions, exhibiting one to three dimensionalities and different topology structures, have been prepared in water medium and structurally characterized by single-crystal X-ray diffraction analysis. Reaction of AgNO 3 with Hima afforded a neutral one-dimensional (1-D) chains [Ag(ima)] n ( 1) which exhibits a pseudo two-dimensional (2-D) layered architecture through π–π stacking interaction between imidazole rings and intermolecular Ag⋯Ag interactions. Reaction of CdCl 2 with Hima yielded neutral 2-D coordination polymers [Cd(ima) 2] n ( 2) possessing (6, 3) topology structures, which further stack into 3-D supramolecular networks through C–H⋯O weak interactions. While Zn(NO 3) 2 was used, a non-centric 3-D coordination polymer [Zn(ima) 2] n ( 3) featuring a 3-fold interpenetrating diamondoid net was isolated. Among these polymers, the building block ima anion exhibits different coordination modes. These results indicate that the versatile nature of this flexible ligand, together with the coordination preferences of the metal ions, play a critical role in construction of these novel coordination polymers. The spectral, thermal and SHG (second-harmonic generation) properties of these new materials have also been investigated.

New infrared nonlinear optical crystalCsGeBr3: synthesis, structure and powder second-harmonic generation properties

An innovative infrared nonlinear optical crystalCsGeBr3 was synthesized. Abinitio calculations on CsGeBr3 were also carried out in order to analyse the second-order nonlinear susceptibilities. From itspowder x-ray diffraction pattern, this crystal was characterized as a rhombohedral structure with an(R3m, No 160) space group symmetry. The reflection powder second-harmonicgeneration (PSHG) measurement of CGBr showed that its nonlinearoptical efficiency is 1.62 times larger than that of rhombohedralCsGeCl3 and is 9.63 timeslarger than that of KH2PO4 (KDP), and most important of all thatCsGeBr3 is phase-matchable.The rescaled deff(2) of CGBr was about 2.45 times larger than that of rhombohedralCsGeCl3, and thistrend was coincident with the ab initio calculation results. The infrared transparent spectrum of rhombohedralCsGeBr3 was extended tomore than 22.5 µm. Therhombohedral CsGeBr3 shows the potential in the realm of nonlinear optics and can be applied to the infraredregion.

Hyperpolarizability Components for α- and ω-Helical Polypeptides in Polar Crystals Determined from Second-Harmonic Generation Measurements

Second-harmonic generation (SHG) properties of α-helical and ω-helical polypeptides have been investigated by using crystalline films prepared by casting lyotropic liquid crystal solutions of poly(γ-phenylpropyl L-glutamate) (3PLG) and poly(β-benzyl L-aspartate) (PBLA) under a high electric field. The crystalline films generated SH light upon irradiation of the Nd:YAG laser, which ensures that the films have a polar structure. The in-plane anisotropy of the polarized SH light intensity is well explained by theoretical descriptions under the C6 and C4 symmetries for 3PLG and PBLA, respectively. On the basis of the SHG results, the hyperpolarizability tensor components of the individual polypeptide helical molecules are characterized as βZXX/βZZZ=1.2, βXZX/βZZZ=3.8, and 2βZXX/βXZX=0.7 for the α-helix 3PLG, and βZXX/βZZZ=3.8, βXZX/βZZZ=5.0, and 2βZXX/βXZX=1.5 for the ω-helix PBLA, where the z-axis is set as the helical axis. Quantum chemical calculation is successfully performed to reveal the general character of the polypeptide helix, βZXX>βZZZ.

Optical homogeneity and second harmonic generation in Li-rich Mg-doped LiNbO 3 crystals

A series of Mg-doped LiNbO 3 crystals were grown using Czochralski method with fixed 5 mol% Mg doping and a variety of Li/Nb ratio (Li/Nb = 0.946–1.08). From the UV–vis absorption spectra, it is found that the absorption edges of the off-congruent crystals successively shift to the violet band in comparison with that of congruent pure LiNbO 3. The birefringence gradient of these crystals was measured to investigate the optical homogeneity. In second harmonic generation (SHG) experiment, the SHG conversion efficiency was enhanced by the Mg doping and the increase of Li/Nb ratio. The dependences of the UV–vis absorption edges, the homogeneity and SHG properties on the Li concentration were explored. The results indicate that the crystal of Li/Nb = 1.02 is the most proper media for SHG application among the five crystals in the paper.

Imaging theory of nonlinear second harmonic and third harmonic generations in confocal microscopy

The imaging theory of nonlinear second harmonic generation (SHG) and third harmonic generation (THG) in confocal microscopy is presented in this paper. The nonlinear effect of SHG and THG on the imaging properties of confocal microscopy has been analyzed in detail by the imaging theory. It is proved that the imaging process of SHG and THG in confocal microscopy, which is different from conventional coherent imaging or incoherent imaging, can be divided into two different processes of coherent imaging. The three-dimensional point spread functions (3D-PSF) of SHG and THG confocal microscopy are derived based on the nonlinear principles of SHG and THG. The imaging properties of SHG and THG confocal microscopy are discussed in detail according to its 3D-PSF. It is shown that the resolution of SHG and THG confocal microscopy is higher than that of single- and two-photon confocal microscopy.

Spectral properties of second-harmonic generation at 800 nm in a BiB3O6 crystal

We have investigated spectral distribution and walk-off effect of second-harmonic generation in a 3-mm-long type I BiB(3)O(6) crystal. Linearly turning ability of the BiB(3)O(6) crystal is confirmed for wavelengths around 800 nm. In addition, the walk-off effect of fundamental beams is quantitatively measured by introducing a little vertical polarization component into pumping fundamental pulses. A conversion efficiency of 28% from fundamental to second harmonic is achieved at a 3.2-GW/cm(2) fundamental intensity.

Origin of Intrinsic Second-Harmonic Generation in Crystallized GeO2–SiO2 Glass Films

The origin and properties of second-harmonic generation (SHG) from crystalline particles and their crystalline phases in GeO2–SiO2 glass films were investigated. GeO2–SiO2 glass films with a thickness of approximately 5 µm were fabricated by the chemical vapor-phase deposition (CVD) method. Heat treatments in the temperature range of 1100–1260°C for durations of 2–8 h have been performed to crystallize the glass films. X-ray diffraction (XRD) peaks at around 2θ=22° in the crystallized GeO2–SiO2 films were observed, and the obtained XRD patterns in the glass films are exactly the same as those in ultraviolet (UV) poled GeO2–SiO2 glasses with a large second-order optical nonlinearity comparable to that in LiNbO3 crystals. Using a SHG microscopic technique, it has been found that the intensity of SHG emission from crystalline particles is clearly dependent on stress-induced optical retardation which is accompanied by the formation of crystalline particles of the pseudo-β-cristobalite containing GeO2. In addition, a new technique for enhancing the intrinsic SHG by means of modification of defect states is demonstrated.