Fabrication and characterization of a third-order nonlinear organic-polymer composite glass waveguide: a self-phase modulator

Composite organic-polymer glass optical waveguides in which coupling to the nonlinear organic-polymer layers was achieved by excitement of the underlying ion-exchanged glass waveguide and coupling of the light to the organic-polymer layer were fabricated and measured. A picosecond pulsed color center laser (λ = 1.5 μm) was used to measure the third-order optical susceptibility χ((3))(-w; w, -w, w) in an organic-dye-polymer composite glass waveguide with a Mach-Zehnder interferometer. For a squaryliumdye-doped poly(methyl methacrylate)-styrene-acrylonitrile matrix polymer layer, a composite χ((3)) of roughly 90, in units of (χLiNbO)(3)((3)), was measured.     

Enhancement of optical nonlinearity in periodic gold nanoparticle arrays

Linear and nonlinear optical properties of periodic triangular Au nanoparticle arrays were investigated. We compared the optical nonlinearity of periodic Au nanoparticle arrays with that of the ultra-thin gold film consisting of randomly distributed spheroidal clusters. A pronounced enhancement of the third-order nonlinear optical susceptibility χ((3)) in Au arrays was observed, and the figure of merit, χ((3))/α, of the periodic nanoparticle arrays is one order of magnitude larger than that of the ultra-thin film. Such an enhancement of the optical nonlinearity could be due to the strong local field near the triangular nanoparticles.     

Extraordinary nonlinear absorption in 3D bowtie nanoantennas

This paper reports that arrays of three-dimensional (3D), bowtie-shaped Au nanoparticle dimers can exhibit extremely high nonlinear absorption. Near-field interactions across the gap of the 3D bowties at the localized surface plasmon resonance wavelengths resulted in an increase of more than 4 orders of magnitude in local field intensity. The imaginary part of the third-order nonlinear susceptibility (Im χ((3))) for the 3D bowtie arrays embedded in a dielectric material was measured to be 10(-4) esu, more than 2 orders of magnitude higher than reported for other metal nanoparticle-dielectric composites. Moreover, 3D dimers with increased nanoscale structure (such as folding) exhibited increased optical nonlinearity. These 3D nanoantennas can be used as critical elements for nanoscale nonlinear optical devices.     

Third-order nonlinear optical properties of sol-gel-derived V(2)O(5), Nb(2)O(5), and Ta(2)O(5) thin films

The third-order nonlinear optical properties of sol-gel-derived V(2)O(5), Nb(2)O(5), and Ta(2)O(5) thin films have been investigated by the third-harmonic-generation method, and the effect of the metal-oxygen bond length on the third-order nonlinear optical susceptibility χ((3)) has been examined. The χ((3)) values of V(2)O(5), Nb(2)O(5), and Ta(2)O(5) thin films were 1.1 × 10(-11), 1.3 × 10(-12), and 6.1 × 10(-13) esu, respectively, which corresponds to an increase in the average bond length I(b) of the order of V-O (I(b) = 0.183 nm), Nb-O (I(b) = 0.200 nm), and Ta-O (I(b) = 0.204 nm). The current and previous results indicate that χ((3)) of these transition metal oxides with the empty d orbitals is dominated mainly by the metal-oxygen bond length rather than the valence of the metal cation. It is predicted on the basis of Lines' model that transition metal oxides with the shortest I(b) exhibit the highest χ((3)), whereas nontransition metal oxides with the longest I(b) exhibit the highest χ((3)).     

Nonlinear refraction and saturable absorption in Au:BaTiO3 composite films

Composite thin films Au:BaTiO3, comprising nanometer-sized gold particles embedded in barium titanate matrices, were synthesized on MgO (100) substrates with the pulsed laser deposition technique. The nanostructure of the films and the size distributions of the Au particles were analyzed by high-resolution transmission electron microscopy. Crystal lattice fringes from the Au nanocrystals and the BaTiO3 matrices were observed. The nonlinear optical properties of the Au:BaTiO3 films were measured with the z-scan method at a wavelength of 532 nm, which was closed to the surface plasmon resonance of nanoscale Au particles. The features of the closed-aperture z-scan transmittance curves were affected by the ratio, which increased greatly at a high metal concentration, of the imaginary part to the real part of the third-order nonlinear susceptibility chi(3).     

Temperature dependence of the third-order nonlinear susceptibility, χ((3)), Of CS(2) and dodecylbenzene

The dependence of the third-order nonlinear susceptibility, χ((3)), of CS(2) and C(18)H(30) (dodecylbenzene) on temperature was measured by the method of degenerate four-wave mixing. The empirical formula for this dependence was obtained. An explanation of this relationship was also given through the application of the model of a polar molecule moving in a viscous medium under the action of a laser beam.     

Nonlinear plasmonics at planar metal surfaces

We investigate the nonlinear optical response of a noble metal surface. We derive the components of the third-order nonlinear susceptibility and determine an absolute value of χ((3))≈0.2 nm(2) V(-2), a value that is more than two orders of magnitude larger than the values found for typical nonlinear laser crystals. Using nonlinear four-wave mixing (4WM) with incident laser pulses of frequencies ω(1) and ω(2), we generate fields oscillating at the nonlinear frequency ω(4WM)=2ω(1)-ω(2). We identify and discuss three distinct regimes: (i) a regime where the 4WM field is propagating, (ii) a regime where it is evanescent, and (iii) a regime where the nonlinear response couples to surface plasmon polaritons.     

Photosensitive gold-nanoparticle-embedded dielectric nanowires

Noble-metal nanoparticles embedded in dielectric matrices are considered to have practical applications in ultrafast all-optical switching devices owing to their enhanced third-order nonlinear susceptibility, especially near the surface-plasmon-resonance (SPR) frequency. Here we present the use of a microreactor approach to the fabrication of a self-organized photosensitive gold nanoparticle chain encapsulated in a dielectric nanowire. Such a hybrid nanowire shows pronounced SPR absorption. More remarkably, a strong wavelength-dependent and reversible photoresponse has been demonstrated in a two-terminal device using an ensemble of gold nanopeapodded silica nanowires under light illumination, whereas no photoresponse was observed for the plain silica nanowires. These results show the potential of using gold nanopeapodded silica nanowires as wavelength-controlled optical nanoswitches. The microreactor approach can be applied to the preparation of a range of hybrid metal-dielectric one-dimensional nanostructures that can be used as functional building blocks for nanoscale waveguiding devices, sensors and optoelectronics.     

碲酸盐系统玻璃组成和结构对非线性光学性能的影响

碲酸盐系统重金属氧化物玻璃是一种优秀的非线性光学玻璃材料，具有较大的三阶非线性光学效应、超快光学响应、较宽红外透过范围、较好稳定性以及广泛应用前景。碲酸盐系统玻璃中的中间离子和网络外离子的加入会改变组成网络的配位多面体组成、键性和能带结构，进而影响玻璃的非线性光学性能。探讨了碲酸盐系统玻璃的网络结构，阐述了玻璃组成、结构以及纳米簇和非线性光学性能之间的相互关系。     

Phase-matched third-harmonic generation in mercury-(I)-chloride

Using phase-matched third-harmonic generation we determine the effective nonlinear susceptibilities in Hg2Cl2 (Calomel) to /chi(3)eff,I/ = 4.5 x 10(-22) m2V(-2) and /chi(3)eff,II/ = 9.7 x 10(-22) m2V(-2) for type I and type II phase matching, respectively. The type III phase matching uses the same tensor components as type I and is deduced to be /chi(3)eff,III/ approximately equal to 1.5 x 10(-22) m2V(-2). The effective third-order susceptibilities of Hg2Cl2 are two orders of magnitude higher than those of CaCO3, and the tensor components chi11 - 3chi18 exceed the components of ADP by a factor of 5. These measurements demonstrate that Calomel might be a promising material to be used for nonlinear optical devices.     

玻璃光学碱度与三阶非线性光学极化率

介绍了玻璃光学碱度的概念,讨论了玻璃光学碱度与三阶非线性光学极化率之间的变化规律,分析了二元硼酸盐、硅酸盐、锗酸盐、碲酸盐、钛酸盐玻璃系统中光学碱度与三阶非线性光学极化率之间变化的定性趋势和定量方程,总结了玻璃光学碱度的本质及其影响,对进一步研究不同玻璃系统中光学碱度与三阶非线性光学极化率之间定量关系的趋势进行了展望.     

Functionalized gold nanoparticles self-assemblies with efficient nonlinear optical properties

Satellite-patterns aggregate structures of gold nanoparticles were fabricated by the inducing pi-pi stacking interactions. The self-assembly process of satellite-patterns was tuned by the controlling ligand exchange on the surface of spherical gold nanoparticles, which provide a novel concept and an efficient method for controlling self-assembly of gold nanoparticles. With increasing the porphyrin alkanethiol ratio (r) of gold nanoparticles, the self-assembly induces to form the larger satellite-structures. The study indicates that exchange process of tetra-n-octylammonium bromide molecules and porphyrin alkanethiol molecules results in the formation of satellite-pattern structures with topological features. Nonlinear optical properties of porphyrin alkanethiol capped gold nanoparticles of toluene solution were measured using the Z-scan technique, and its third-order nonlinear optical susceptibility (chi(3)) is calculated as 0.9 x 10(-13) esu, presented the third-order nonlinear optical properties. The well-ordered assembly of gold nanoparticles exhibits controlled the third-order nonlinear optical properties, which can be enhanced with the increasing of the porphyrin alkanethiol ratio in systems.     

Large third-order optical nonlinearity in directly synthesized single-walled carbon nanotube films

Large third-order optical nonlinearity is observed in single-walled carbon nanotube (SWNT) films that are directly synthesized by CVD method rather than post-deposited from solution. Through z-scan method, the third-order nonlinear susceptibility (chi(3)) is measured, and the |Im chi(3)| is 1.8 x 10(-7) esu at 1064 nm, which is among the highest reported values for optical nonlinear materials. Combined with their transparent morphology and ultrafast carrier relaxation time, our results indicate the promising prospect of directly synthesized SWNT films as saturable absorbers using in mode-lock lasers or ultrafast switching materials in optical telecommunications.     

Two-photon absorption and degenerate four-wave mixing studies of sulfide semiconductor nanoparticles in polymeric solutions

The two-photon absorption coefficients (beta) and the third-order nonlinear susceptibilities (chi(3)) of several semiconductor nanoparticles (CdS, Cd(x)Ag(1-x)S, and core-shell CdS/Ag2S) that are confined and stabilized by random and block ionomers have been measured by nonlinear transmission and degenerate four-wave mixing techniques using 21 picosecond laser pulses at near-infrared spectral region. The imaginary part of the third-order nonlinear susceptibility that is related to the two-photon absorption coefficient was then calculated. The absorptive nonlinearity of the nanoparticles (2 approximately 9 nm) was found to be dependent on the particle size, composition and wavelength, i.e., larger CdS particles exhibit higher two-photon absorption coefficients and the presence of Ag improves two-photon absorption of CdS nanoparticles. The obtained two-photon absorption coefficients of nanoparticles corrected for their volume fraction in solution are significantly greater that those of corresponding bulk semiconductors.     

Quantum-enhanced tunable second-order optical nonlinearity in bilayer graphene

Second order optical nonlinear processes involve the coherent mixing of two electromagnetic waves to generate a new optical frequency, which plays a central role in a variety of applications, such as ultrafast laser systems, rectifiers, modulators, and optical imaging. However, progress is limited in the mid-infrared (MIR) region due to the lack of suitable nonlinear materials. It is desirable to develop a robust system with a strong, electrically tunable second order optical nonlinearity. Here, we demonstrate theoretically that AB-stacked bilayer graphene (BLG) can exhibit a giant and tunable second order nonlinear susceptibility χ((2)) once an in-plane electric field is applied. χ((2)) can be electrically tuned from 0 to ~10(5) pm/V, 3 orders of magnitude larger than the widely used nonlinear crystal AgGaSe(2). We show that the unusually large χ((2)) arise from two different quantum enhanced two-photon processes thanks to the unique electronic spectrum of BLG. The tunable electronic bandgap of BLG adds additional tunability on the resonance of χ((2)), which corresponds to a tunable wavelength ranging from ~2.6 to ~3.1 μm for the up-converted photon. Combined with the high electron mobility and optical transparency of the atomically thin BLG, our scheme suggests a new regime of nonlinear photonics based on BLG.     

Microscale Synthesis of Fe(PF(3))(5) for Gas Source Mass Spectrometry

Down-scaling of a cocondensation method to produce volatile pentakis(trifluorophosphine)iron(0) for measuring isotope ratios by gas source mass spectrometry is described. Starting from 10 mg of iron, this method allows synthesis of a sufficient amount of Fe(PF(3))(5) that can be used to measure iron content and/or isotope ratios in real-life samples. The advantage over thermal ionisation mass spectrometry is that more precise determinations of ratios/amounts are possible. Reproducibilities for n((54)Fe)/n((56)Fe) and n((57)Fe)/n((56)Fe) are (1-3) × 10(-4), while those obtained by thermal ionization mass spectrometry are at the 10(-3) level.     

The operator tensor formulation of quantum theory

In this paper, we provide what might be regarded as a manifestly covariant presentation of discrete quantum theory. A typical quantum experiment has a bunch of apparatuses placed so that quantum systems can pass between them. We regard each use of an apparatus, along with some given outcome on the apparatus (a certain detector click or a certain meter reading for example), as an operation. An operation (e.g. B(b(2)a(3))(a(1))) can have zero or more quantum systems inputted into it and zero or more quantum systems outputted from it. The operation B(b(2)a(3))(a(1)) has one system of type a inputted, and one system of type b and one system of type a outputted. We can wire together operations to form circuits, for example, A(a(1))B(b(2)a(3))(a(1))C(b(2)a(3)). Each repeated integer label here denotes a wire connecting an output to an input of the same type. As each operation in a circuit has an outcome associated with it, a circuit represents a set of outcomes that can happen in a run of the experiment. In the operator tensor formulation of quantum theory, each operation corresponds to an operator tensor. For example, the operation B(b(2)a(3))(a(1)) corresponds to the operator tensor B(b(2)a(3))(a(1)). Further, the probability for a general circuit is given by replacing operations with corresponding operator tensors as in Prob(A(a(1))B(b(2)a(3))(a(1))C(b(2)a(3))) = ?(a(1))B(b(2)a(3))(a(1))C(b(2)a(3)). Repeated integer labels indicate that we multiply in the associated subspace and then take the partial trace over that subspace. Operator tensors must be physical (namely, they must have positive input transpose and satisfy a certain normalization condition).     

Optical nonlinearities of Au nanocluster composite fabricated by 250 keV ion implantation

Metal nanocluster composite glass prepared by 250 keV Au ions into silica with dose of 1 × 10¹⁷ ions/cm² has been studied. The microstructural properties of the nanoclusters are characterized by optical absorption spectra and transmission electron microscopy (TEM). Third-order optical properties of the nanoclusters are studied by the Z-scan technique under 1064 nm and 532 nm excitations. The nonlinear refraction index, nonlinear absorption coefficient, and the real and imaginary parts of the third-order nonlinear susceptibility are deduced. The results of the investigation of nonlinear refraction using the off-axis Z-scan configuration are presented and the mechanisms responsible for the nonlinear response are discussed. The third-order nonlinear susceptibility χ⁽³⁾ of this kind of sample was determined to be 1.6 × 10⁻⁷ esu at 532 nm and 1.3 × 10⁻⁷ esu at 1064 nm.     

Studies of third-order optical nonlinearities and optical limiting of 2, 3-butanedione dihydrazone

2, 3-butanedione dihydrazone (BDDH) synthesized via chemical route and nonlinear optical parameters, such as nonlinear refractive index (n2), nonlinear absorption coefficient (β), third-order nonlinear optical susceptibility (χ(3)), second hyperpolarizability (γ), and optical-limiting behavior were investigated by single beam z-scan technique for different concentrations. Synthesized sample were irradiated by a Q-switched, frequency doubled Nd:YAG laser and found that n2 and β increases linearly with increasing concentration and hence γ decreases linearly. The excited-state absorption cross sections of BDDH were found to be larger than ground-state absorption cross sections, and it leads to reverse saturable absorption (RSA). The experimental results are well in agreement with the theory and also establish BDDH as one of the potential candidate materials for optical limiting at 532 nm.     

二氧化钛薄膜的三阶非线性光学特性

采用脉冲激光沉积技术在熔石英基片上制备了c轴取向的锐钛矿相TiO₂薄膜.通过X射线衍射和原子力显微镜对薄膜的结构、结晶性和表面特性进行了表征.通过透射光谱计算得到TiO₂薄膜折射率约为2.1,光学带隙约为3.18eV.结合飞秒激光和Z扫描方法测量了薄膜的超快非线性光学特性,结果表明：锐钛矿TiO₂薄膜具有负的非线性吸收系数和负的非线性折射率,其大小分别为-6.2×10^-11m/W和-6.32×10^-17m²/W,对应的三阶非线性极化率的实部和虚部分别为-7.1×10^-11esu和-4.42×10^-12esu.并计算薄膜的优值比T=βλ/n₂≈0.8,表明锐钛矿相的TiO₂在非线性光学器件方面具有潜在的应用前景.