Third-order Nonlinear Optical Effects Research Articles

矢量光场激发三阶非线性光学效应的研究进展（特邀）

矢量光场激发三阶非线性光学效应的研究进展（特邀）

Nonlinear optical response spatial self-phase modulation in MoTe2: correlations between χ(3) and mobility or effective mass.

We report on an unambiguous observation of the third-order nonlinear optical effect, spatial self-phase modulation (SSPM), in a MoTe2 dispersion. The values of the third-order nonlinear optical coefficients effectively for one-layer MoTe2, χone-layer(3), are obtained through the SSPM method at excitation wavelengths 473, 532, 750, and 801nm, respectively. The wind-chime model is used to explain the ring formation time. The wavelength dependence of χone-layer(3) compares well with the photo-absorption spectra. Significantly, we find a correlation between χ(3) and the carrier mobility μ or effective mass m*, which again further supports the laser-induced ac electron coherence in 2D materials.

Optical phase-change in plasmonic nanoparticles by a two-wave mixing

Described herein is the optical phase-change and photothermal phenomena induced by a two-wave mixing configuration in a nonlinear optical material. For experimental analysis of these findings, the third-order nonlinear optical response exhibited by bimetallic Au–Pt nanoparticles embedded in a TiO2 matrix was studied. A vectorial two-wave mixing technique was conducted to explore the automatic generation of polarized self-diffraction by the participation of the optical Kerr effect in the samples. Fractional derivative calculations allowed us to identify the physical mechanism responsible for photothermal influence on the third-order nonlinear optical effects in the nanosystems. A 532 nm wavelength emitted by the second harmonic of a nanosecond Nd:YAG laser system was employed as an optical source in our measurements. Based on the importance of the vectorial nature of light for dictating the amplitude of the beams and splitting properties, within this work is highlighted the attractive energy transfer functions and phase modulation that can be envisioned by photothermally-controlled interactions.

Vector beams excited nonlinear optical effects

Vector beams with the desired polarization structure interacting with matter result in many novel nonlinear optical effects. Herein, we review the tight focusing and weak focusing properties of three types of light beams, namely, linearly polarized beams, cylindrical vector beams, and hybridly polarized beams. In particular, we revisit the second- and third-order nonlinear optical effects in nonlinear optical media under the excitation of several types of vector beams with the desired polarization distribution. The prospects of their applications in nonlinear optical microscopy and materials characterization are also briefly discussed.

Broadband nonlinear optical resonance and all-optical switching of liquid phase exfoliated tungsten diselenide

As a kind of two-dimensional transition metal dichalcogenide material, tungsten diselenide (WSe2) has attracted increasing attention, owing to its gapped electronic structure, relatively high carrier mobility, and valley pseudospin, all of which show its valuable nonlinear optical properties. There are few studies on the nonlinear optical properties of WSe2 and correlation with its electronic structure. In this paper, the effects of spatial self-phase modulation (SSPM) and distortion influence of WSe2 ethanol suspensions are systematically studied, namely, the nonlinear refractive index and third-order nonlinear optical effect. We obtained the WSe2 dispersions SSPM distortion formation mechanism, and through it, we calculated the nonlinear refractive index n2, nonlinear susceptibility χ(3), and their wavelength dependence under the excitation of 457 nm, 532 nm, and 671 nm lasers. Moreover, by use of its strong and broadband nonlinear optical response, all-optical switching of two different laser beams due to spatial cross-phase modulation has been realized experimentally. Our results are useful for future optical devices, such as all-optical switching and all-optical information conversion.

Synthesis and enhanced third-order nonlinear optical effect of ZnSe/graphene composites

ZnSe/graphene composites are produced by chemical method, and the attachment of ZnSe nanocrystals on graphene nanosheets can be confirmed by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and UV-vis spectroscopy. The nonlinear optical properties are investigated at 532 nm by a picosecond laser Z-scan technique. It is found that the interaction between ZnSe and graphene enhances the optical nonlinearity of ZnSe/graphene composites than single ZnSe or graphene. The increase of ZnSe size further enhances the optical nonlinearity of ZnSe/graphene.

Amplitude-modulated acoustic waves by nonlinear optical signals in bimetallic Au-Pt nanoparticles and ethanol based nanofluids

Acoustic waves were propagated through bimetallic Gold and Platinum nanoparticles suspended in ethanol in order to analyze their modification in amplitude by the assistance of third-order nonlinear optical effects. Nanosecond pulses at 532 nm wavelength were able to modify the acoustic transmittance by shifting the resonance of the mechanical vibration modes of the sample contained in a quartz cuvette. The optical Kerr effect exhibited by the nanoparticles was identified to be responsible for third-order optical nonlinearities that caused important changes in density associated with the sample. The nanofluids were prepared by a sol-gel method and explored by a vectorial two-wave mixing experiment. The nanostructured nature of the samples was evaluated by standard UV–Vis spectroscopy, high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy measurements. Potential applications for developing optomechanic nanosystems sensitive to pressure driven by optical nonlinearities can be contemplated.

XOR Logic Gate by Carbon/Metal Nanoinks Based on a Double-Stage Optical Kerr Gate Configuration

Two-input binary exclusive-or logic operations were presented by the assistance of multiwall carbon nanotubes in a double-stage optical Kerr gate scheme with two control beams. The samples were prepared by the aerosol pyrolysis method and decorated by platinum nanoparticles using a chemical vapor deposition technique. The nanostructures were suspended in ethanol to obtain carbon/metal nanoinks with different concentrations and then randomly distributed networks integrated in thin film form were fabricated. Polarization-selectable functions were obtained in the double-stage scheme by using nanosecond third-order nonlinear optical effects at 532 nm wavelength exhibited by the samples. Potential applications for ultrafast identification and encryption of nonlinear optical signals were discussed.

Acousto-Optic Logic Gate Controlled by Third-Order Nonlinear Optical Effects in Bimetallic Au-Pt Nanoparticles

Acousto-Optic Logic Gate Controlled by Third-Order Nonlinear Optical Effects in Bimetallic Au-Pt Nanoparticles

Quadratic electro-optic Kerr effect in doped graphene

We theoretically investigate one of the third-order nonlinear optical (NLO) effects, namely, the quadratic electro-optic Kerr effect (EOKE), in doped graphene. To avoid the screening of an in-plane external dc electric field by the graphene’s electrons, we propose to use ‘low-amplitude’ ( cm−1) terahertz radiation pulses focused onto the graphene sample collinearly with a normally incident optical beam of frequency ω. Using the Dirac cone approximation for the π-electron energy bands of graphene, we calculate the real part of the effective third-order NLO susceptibility , describing the EOKE in doped graphene under the above conditions. The results obtained show that a large electro-optic modulation of the graphene’s refractive index n (up to ) can be achieved by proper tuning the Fermi level of charge carriers in the graphene sample via electrostatic gating. Furthemore, a change of sign of the electro-optic Kerr coefficient of doped graphene can occur in the spectral range below the photon energy threshold value of , corresponding to the onset of the fundamental (single-photon) interband absorption in the graphene. These theoretical findings open up new opportunities for practical exploitation of the EOKE in graphene-based NLO devices.

Editorial expression of concern on intermediate Ce3+ defect level induced photoluminescence and third-order nonlinear optical effects in TiO2–CeO2 nanocomposites by S. Divya, V. P. N. Nampoori, P. Radhakrishnan, and A. Mujeeb

Editorial expression of concern on intermediate Ce3+ defect level induced photoluminescence and third-order nonlinear optical effects in TiO2–CeO2 nanocomposites by S. Divya, V. P. N. Nampoori, P. Radhakrishnan, and A. Mujeeb

Tungsten(VI)-Copper(I)-Sulfur Cluster-Supported Metal-Organic Frameworks Bridged by in Situ Click-Formed Tetrazolate Ligands.

Six analogous two-dimensional (2D) [Tp*WS3Cu3]-based (Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate) networks, namely, {[(Tp*WS3Cu3)2L3](μ3-N3)}n (2: L = 5-methyltetrazolate (Mtta); 3a: L = 5-ethyltetrazolate (Etta)) and {[(Tp*WS3Cu3)2L3]BF4}n (3b: L = Etta; 4: L = 5-propyltetrazolate (Ptta); 5: L = 5-butyltetrazolate (Btta); 6: L = 5-pentyltetrazolate (Petta)) were synthesized by reactions of [Et4N][Tp*WS3] (1), [Cu(CH3CN)4]BF4, NaN3, and NH4BF4 in different nitrile solvents (CH3(CH2)nCN, n = 0, 1, 2, 3, and 4) under solvothermal conditions. In the structures of 2-6, each alkyl tetrazolate L as a bridging ligand was generated in situ from the "click" reaction between azide and nitrile. These 2D (6,3) networks support two types of voids wherein the pendant alkyl groups are accommodated. A tetrahedron cage-like cluster [Tp*W(μ3-S)3(μ3-S')Cu3]4 (7) was also formed in some of the above reactions and can be readily separated by solvent extraction. The proportion of 7 increased with the elongation of the alkyl chains and finally became the exclusive product when heptylnitrile was employed. Further use of CuCN as a surrogate for [Cu(CH3CN)4]BF4 with the aim of introducing additional CN bridges into the network led us to isolate a tetrazolate-free compound, {[Et4N]{(Tp*WS3Cu3)[Cu2(CN)4.5]}2·2PhCH2CN}n (8·2PhCH2CN), a unique 2D network that features {(Tp*WS3Cu3)[Cu2(CN)5]}22-, {(Tp*WS3Cu3)3[Cu3(CN)7]2[Cu(CN)3]}4-, and {(Tp*WS3Cu3)[Cu4(CN)9]}26- ring subunits. Compounds 5-8 are soluble in DMF and exhibit a reverse saturable absorption and self-focusing third-order nonlinear optical (NLO) effect at 532 nm with hyperpolarizability γ values in the range of 4.43 × 10-30 to 5.40 × 10-30 esu, which are 400-500 times larger than that of their precursor 1. The results provide an interesting insight into the synergetic synthetic strategy related to the assembly of the [Tp*WS3Cu3]2+ cluster core, the "click" formation of the tetrazolate ligands, and the construction of the [Tp*WS3Cu3]2+ cluster-based 2D networks.

Magneto-conductive encryption assisted by third-order nonlinear optical effects in carbon/metal nanohybrids

The influence of a magnetic field on electrical conductivity and the third-order nonlinear optical properties exhibited by carbon nanotubes decorated with platinum nanoparticles is reported. The experimental and numerical results of the nonlinear magneto-optics, magneto-conductivity and photo-thermal processes were analyzed. The simultaneous impact of optical absorptive nonlinearities and the magnetic field in the sample allowed us to encrypt information in the electronic signals by designing an exclusive-OR logic gate scheme. The samples were prepared in film form using a spray pyrolysis route and a chemical vapor deposition approach. The characterization of the morphological nature of the multiwall nanotubes was evaluated by transmission electron microscopy and x-ray techniques. A vectorial two-wave mixing method was conducted by using nanosecond pulses at 532 nm in order to estimate the nonlinear optical behavior in the nanohybrid materials explored. An important enhancement in the phonon-band-structured transport from the inclusion of nanoparticles in the nanotubes was numerically calculated. A distinguished modification in the transient dynamics of the photo-thermal transitions and Kerr nonlinearities was pointed out to be due to the metallic nanoparticles incorporated in the sample. An extraordinary evolution of the magneto-conductivity, together with a strong change in the optical Kerr transmittance exposed to the magnetic field in propagation through the nanostructures, was observed.

Coherent Nonlinear Optical Response Spatial Self-Phase Modulation in MoSe2 Nano-Sheets

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are drawing increasing interest due to their relatively high carrier mobilities, valley pseudospins, and gapped electronic structures, which all indicate interesting nonlinear optical properties of these 2D materials. However, such nonlinear optical properties are so far less investigated and their correlation with the electronic structure of the material is rarely probed. In this work, we have systematically investigated the spatial self-phase modulation (SSPM) of MoSe2 flakes in a suspension form, which is a coherent third-order nonlinear optical effect. The nonlinear susceptibility χ(3) and its wavelength-dependence are measured, yielding a value of 1.1 × 10−9 e.s.u. (SI: 1.53 × 10−17 m2/V2) at 532 nm laser excitation for effective one-layer MoSe2.

Single MoO3 nanoribbon waveguides: good building blocks as elements and interconnects for nanophotonic applications.

Exploring new nanowaveguide materials and structures is of great scientific interest and technological significance for optical and photonic applications. In this work, high-quality single-crystal MoO3 nanoribbons (NRs) are synthesized and used for optical guiding. External light sources are efficiently launched into the single MoO3 NRs using silica fiber tapers. It is found that single MoO3 NRs are as good nanowaveguides with loss optical losses (typically less than 0.1 dB/μm) and broadband optical guiding in the visible/near-infrared region. Single MoO3 NRs have good Raman gains that are comparable to those of semiconductor nanowaveguides, but the second harmonic generation efficiencies are about 4 orders less than those of semiconductor nanowaveguides. And also no any third-order nonlinear optical effects are observed at high pump power. A hybrid Fabry-Pérot cavity containing an active CdSe nanowire and a passive MoO3 NR is also demonstrated, and the ability of coupling light from other active nanostructures and fluorescent liquid solutions has been further demonstrated. These optical properties make single MoO3 NRs attractive building blocks as elements and interconnects in miniaturized photonic circuitries and devices.

Phase retrieval via regularization in self-diffraction-based spectral interferometry

A novel variant of spectral phase interferometry for direct electric-field reconstruction (SPIDER) is introduced and experimentally demonstrated. Unlike most previously demonstrated variants of SPIDER, our method is based on a third-order nonlinear optical effect, namely self-diffraction (SD), rather than the second-order effect of sum-frequency generation. On the one hand, SD substantially simplifies phase-matching capabilities for multioctave spectra that cannot be hosted by second-order processes given manufacturing limitations of crystal lengths in the few-micrometer range. However, on the other hand, SD SPIDER imposes an additional constraint as it effectively measures the spectral phase of a self-convolved spectrum rather than immediately measuring the fundamental phase. Reconstruction of the latter from the measured phase and the spectral amplitude of the fundamental turns out to be an ill-posed problem, which we address by a regularization approach. We discuss the numerical implementation in detail and apply it to measured data from a Ti:sapphire amplifier system. Our experimental demonstration used 54 fs pulses and a 500 μm thick BaF2 crystal to show that the SD SPIDER signal is sufficiently strong to be separable from stray light. Extrapolating these measurements to the thinnest conceivable nonlinear media, we predict that bandwidths well above two optical octaves can be measured by a suitably adapted SD SPIDER apparatus, enabling the direct characterization of pulses down to single-femtosecond pulse durations. Such characteristics appear out of range for any currently established pulse measurement technique.

Third-Harmonic Generation in Ultrathin Films of MoS2

We observe optical third-harmonic generation in atomically thin films of MoS2 and deduce effective third-order nonlinear susceptibilities on the order of 10(-19) m(2)/V(2), which is comparable to that of commonly used semiconductors under resonant conditions. By measuring the susceptibility as a function of light wavelength, we find significant enhancements of the susceptibility by excitonic resonances. The demonstrated third-harmonic generation can be used for nonlinear optical identification of MoS2 atomic layers with high contrast, better distinguishing power of multilayers, and less restrictions to substrate selections. The size of the third-order nonlinear susceptibility suggests feasibility of exploring other types of third-order nonlinear optical effects of MoS2 two-dimensional crystals.

Intermediate Ce3+ defect level induced photoluminescence and third-order nonlinear optical effects in TiO2–CeO2 nanocomposites

Intermediate Ce3+ defect level induced photoluminescence and third-order nonlinear optical effects in TiO2–CeO2 nanocomposites

Intermediate Ce3+ defect level induced photoluminescence and third-order nonlinear optical effects in TiO2–CeO2 nanocomposites

We report on the linear and nonlinear optical studies of TiO2–CeO2 nanocomposites. It was found that the band gap of the nanocomposite can be tuned by varying Ce/Ti content. Nonlinear absorption characteristics of these samples were studied by employing open aperture Z-scan technique using an Nd:YAG laser (532 nm, 7 ns, 10 Hz). It has been observed that as the CeO2 amount increases, band gap of the nanocomposites decreases and the reason proposed for the change in band gap is the smudging of localised states of Ce3+ into the forbidden energy gap, thus acting as the intermediate state. Fluorescence studies confirmed the above argument. Nonlinear investigation revealed that with increase in the CeO2 amount, the two-photon absorption coefficient increased due to the modification of TiO2 dipole symmetry. Suitable candidature of the nanocomposites for the fabrication of nonlinear optical devices was proved by determining the optical limiting threshold.

Absorption and nonlinear optical properties of Te/TeO2-SiO2 composite films

The transmission and absorption spectra of the Te/TeO2-SiO2 thin film were obtained by using a spectrophotometer, with the surface plasmon rensoance (SPR) observed at 480 nm. While the dependence of the third-order nonlinear susceptibility of composite films on the Te particle was investigated by Z-scan technique with renosant wavelength (532 nm) and non-renosant wavelength (1064 nm). Optical properties of these films was analyzed using the effective medium theory, and the relationship was investigated to obtain Te particle size and nonlinear optical properties of Te/TeO2-SiO2 films. The results show that the Te particle size was smaller, the number of particles was increased, and the particle distribution tends to be uniform. The surface plasmon resonance peak was red-shifted, and the absorption intensity was enhanced; and the third-order nonlinear optical effects was enhanced, χ(3) was increased by 5.12×10-7 esu at 1064 nm to 8.11×10-7 esu at 532 nm with preparation potential increased.