The third-order optical nonlinearity of Bi3.25La0.75Ti3O12 ferroelectric thin film on quartz

Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin film was prepared on quartz substrates using chemical solution deposition. The sign and magnitude of both real and imaginary parts of third-order nonlinear susceptibility χ⁽³⁾ of the BLT thin film have been determined by the Z-scan technique performed at 800 nm with a femtosecond laser. The nonlinear refractive index coefficient γ and the nonlinear absorption coefficient β of the BLT thin film are − 1.915 × 10^− 12 cm² / W and − 6.764 × 10^− 8 m/W, respectively, the real part and imaginary part of the third-order nonlinear susceptibility χ⁽³⁾ of the BLT thin film are − 5.81 × 10^− 18 m² / V² and − 1.31 × 10^− 18 m² / V², respectively. Both the real and the imaginary parts of the third-order nonlinear susceptibility χ⁽³⁾ contribute to the nonlinearity of the film. These experimental results show that BLT thin film is a promising material for applications in nonlinear optical devices.     

Organic materials for nonlinear optics

This review discusses nonlinear optical (NLO) polymeric materials. As an example of a second-order NLO material, a novel copolymer with a diazo dye attached is investigated. The second-order NLO coefficient χ⁽²⁾ of the copolymer reaches 1.0 × 10^?6 esu, which is 7 times larger than that of LiNbO₃. A third-order NLO coefficient χ⁽³⁾ larger than 10^?10 esu is obtained for polymers where NLO dyes are introduced into the polymer backbone. The optical transmission loss of these polymers is revealed to be around 2 dB/cm. As these polymers can be formed into channel waveguides using the photo-bleaching technique, they show promise for use in NLO devices because of their processability, transparency and large optical nonlinearity.     

Large resonant third-order optical nonlinearity of thin film containing J-like aggregates of a bis[4-(N-dibutylamino)phenyl]squarylium dye

The third-order optical nonlinearity and response of thin film containing J-like aggregates of a bis[4-(N-dibutylamino)phenyl]squarylium dye were measured by degenerate four-wave mixing (DFWM) technique under resonant conditions. The temporal profile of DFWM signal was obtained with a time resolution of 0·3 ps (FWHM), and was found to consist of at least two components, i.e. the coherent instantaneous nonlinear response (electronic response) and the slow response due to the excited state population grating. The effective χ ⁽³⁾ value of thin squarylium dye film was evaluated to be as high as 1·1 × 10^???7 esu, and the figure of merit of third-order nonlinearity F (F =?χ ⁽³⁾/α), was calculated to be about 2·1 × 10^???13 esu cm.     

Exceptionally large third-order optical susceptibility in Ag:SrBi2Nb2O9 composite films

Thin films of SrBi₂Nb₂O₉ with and without the inclusion of Ag nanocrystals were prepared on MgO (001) substrates by alternative pulsed laser ablation of SrBi₂Nb₂O₉ ceramic and Ag metal in a nitrogen atmosphere. The size of the Ag nanocrystals can be brought down to ca. 5.0 nm, as revealed by transmission electron microscopy and X-ray diffraction. We measured the third-order susceptibility χ⁽³⁾ of the deposits by single beam z-scan technique at a wavelength of 532 nm. It is found that SrBi₂Nb₂O₉ is an effectively nonlinear optical medium, exhibiting a very large χ⁽³⁾. With the inclusion of Ag nanocrystals the χ⁽³⁾ was nearly doubled (Reχ⁽³⁾ = 8.052 × 10^− 7 esu, and Imχ⁽³⁾ = − 1.717 × 10^− 7 esu), which comes very close to the maximum value available in the current time. This indicates that the Ag:SrBi₂Nb₂O₉ composite structure can be an excellent candidate for nonlinear optical applications. A general approach for further enhanced third-order susceptibility by tailoring the dielectric constant of the metal inclusion is briefly discussed.     

Third-order nonlinear optical responses of nanoparticulate Co3O4 films

Third-order nonlinear optical responses of nanoparticulate Co₃O₄ films, prepared by sputtering and pyrolysis, were investigated. The sputtered Co₃O₄ film showed a large third-order nonlinear susceptibility (|χ⁽³⁾|) of 3.2×10⁻⁸ esu, determined by degenerate four-wave mixing (DFWM). This |χ⁽³⁾| is 7.1 times greater than that of the pyrolyzed Co₃O₄ film, attributable to the greater density and refractive index of the sputtered film. Time-resolved DFWM experiments show a slowly decaying component with a lifetime of approximately 100 ps existing for both films in addition to a fast decaying component. Nonlinear transmission experiments revealed both films exhibiting significant nonlinear absorption. The imaginary part of the susceptibility (Im[χ⁽³⁾]) found for each film was of the same order of magnitude as the |χ⁽³⁾| found by the DFWM method, showing that the major part of the fast decaying component of |χ⁽³⁾| comes from the nonlinear absorption.     

Surface plasmon-enhanced third-order optical non-linearity of silver triangular nanoplate

Abstract

We have obtained Ag triangular nanoplates with plasmon resonance bands locating from 750 to 950 nm by wet chemical method. The third-order optical non-linear response property of Ag triangular nanoplate is investigated using z-scan technique. The incident wavelength dependence of χ⁽³⁾ (the third-order susceptibility) shows the third-order nonlinear behaviour of Ag nanoplate is greatly modified by its plasmon resonance property, for the largest value of χ⁽³⁾ is observed around the wavelength of plasmon resonant peak. Also, we find the maximum value of Ag nanoplate’s χ⁽³⁾ is 7.46 × 10^?11 esu, which is about 1–3 orders of magnitude larger than that of many other nanomaterials including Au nanorod, nanobipyramid and nanocube, as well as Ag nanosphere and nanodisc. This fact indicates the Ag triangular nanoplate is a kind of useful nonlinear material with larger third-order nonlinearity, showing great potentials in the explorations of functional non-linear devices.     

Large third-order optical nonlinearity of SrBi2Nb2O9 thin films fabricated by pulsed laser deposition

SrBi₂Nb₂O₉ (SBN) thin films with a single phase of layered perovskite structure have been fabricated on fused quartz substrates at room temperature by pulsed laser deposition. The XRD and AFM analysis indicated that the films had better crystallinity, less rough surface morphology, and larger grain size with increasing oxygen pressure. The nonlinear optical properties of the samples were determined using a single beam Z-scan technique at a laser wavelength of 532 nm with laser duration of 25 ps. The real and imaginary parts of the third-order nonlinear optical susceptibility χ⁽³⁾ of the films were measured to be 3.18 × 10^− 8 esu and 5.94 × 10^− 9 esu, respectively.     

Third-order nonlinear optical properties of Bi2S3 nanocrystals doped in sodium borosilicate glass studied with Z-scan technique

The third-order nonlinear optical properties of Bi₂S₃ nanocrystals doped in sodium borosilicate glass are measured by Z-scan technique. The microstructures of the glass are characterized by means of X-ray diffraction, transmission electron microscopy, scanning transmission electron microscopy, energy dispersion X-ray spectra, and high-resolution transmission electron microscopy. The results show that the Bi₂S₃ nanocrystals ranging from 10 to 30 nm are determined to be of the orthorhombic crystalline phase, and the third-order optical nonlinear refractive index γ, absorption coefficient β, and susceptibility χ⁽³⁾ of the glass are determined to be 2.56 × 10⁻¹⁶ m² W⁻¹, 4.13 × 10⁻¹⁰ mW⁻¹, and 1.43 × 10⁻¹⁰ esu, respectively.     

Nonlinear optical response of silica doped with copper nanoclusters under 1064 nm laser excitation

Metal nanocluster composite glass was formed by Cu ion implantation into silica using metal vapor vacuum arc (MEVVA) ion source. The microstructural properties of the nanoclusters were analyzed by optical absorption spectra and transmission electron microscopy (TEM). Third-order nonlinear optical properties of the nanoclusters were measured at 1064 nm excitations using Z-scan technique. The nonlinear refraction index, nonlinear absorption coefficient, and the real and imaginary parts of the third-order nonlinear susceptibility were deduced. The mechanisms responsible for the nonlinear response were discussed. Third-order nonlinear susceptibility χ⁽³⁾ of this kind of sample was determined to be (4.2 ± 1.0) × 10⁻⁸ esu.     

Preparation and nonlinear optical response of novel palladium-containing micellar nanohybrids

The synthesis and characterization of novel micellar nanohybrids with controllable sizes consisting of palladium nanosized core and covered by well-defined poly(lauryl methacrylate)-block-poly(2-(acetoacetoxy)ethyl methacrylate) (pLauMA-b-pAEMA) diblock copolymers are reported. Their nonlinear optical (NLO) response (i.e. nonlinear refraction and absorption and the third-order susceptibility χ⁽³⁾) is also studied under 35 ps laser excitation both in the visible and in the infrared and found to be insensitive to the size of the micelles while it was found to be greatly affected by the molar fraction of the AEMA block. To the best of our knowledge it is the first time that such Pd micellar nanohybrids are synthesized and investigated towards their NLO properties. The magnitude of the nonlinear optical response of these nanohybrids renders them promising candidates for potential optoelectronic applications.     

Gold nanoparticles incorporated mesoporous silica thin films of varied gold contents and their well-tuned third-order optical nonlinearities

Gold nanoparticles (NPs) incorporated mesoporous silica thin films (MSTFs) of varied gold contents from 4.64 to 29.15 wt.% were synthesized through a refined chemical modification to the mesopore surface using different amounts of silane with amino end group. The microstructures of the composite thin films were characterized and the off-resonant third-order optical nonlinearities of the composite thin films were investigated by Z-scan technique at 1064 nm. The resultant composite thin films showed increased third-order optical nonlinear susceptibility (χ⁽³⁾) from 4.26 × 10⁻¹¹ to 9.24 × 10⁻¹⁰ esu at increased gold contents. The dependence of χ⁽³⁾ on gold content have been discussed, which can be described by an exponent function y = y₀ + Ae^−x/t when the gold contents of the composite thin films were below 30 wt.%.     

Ab-initio and DFT methodologies for computing hyperpolarizabilities and susceptibilities of highly conjugated organic compounds for nonlinear optical applications

In this talk, after a short introduction on the methodologies used for computing dipole polarizability (α), second and third-order hyperpolarizability and susceptibility; the results of theoretical studies performed on density functional theory (DFT) and ab-initio quantum mechanical calculations of nonlinear optical (NLO) properties for a few selected organic compounds and polymers will be explained. The electric dipole moments (μ) and dispersion-free first hyperpolarizabilities (β) for a family of azo-azulenes and a styrylquinolinium dye have been determined by DFT at B3LYP level. To reveal the frequency-dependent NLO behavior, the dynamic α, second hyperpolarizabilities (γ), second (χ⁽²⁾) and third-order (χ⁽³⁾) susceptibilites have been evaluated using time-dependent HartreeFock (TDHF) procedure. To provide an insight into the third-order NLO phenomena of a series of pyrrolo-tetrathiafulvalene-based molecules and pushpull azobenzene polymers, two-photon absorption (TPA) characterizations have been also investigated by means of TDHF. All computed results of the examined compounds are compared with their previous experimental findings and the measured data for similar structures in the literature. The one-photon absorption (OPA) characterizations of the title molecules have been theoretically obtained by configuration interaction (CI) method. The highest occupied molecular orbitals (HOMO), the lowest unoccupied molecular orbitals (LUMO) and the HOMO–LUMO band gaps have been revealed by DFT at B3LYP level for azo-azulenes, styrylquinolinium dye, push–pull azobenzene polymers and by parametrization method 6 (PM6) for pyrrolo-tetrathiafulvalene-based molecules.     

Enhancement of optical nonlinearity in binary metal-nanoparticle arrays

Periodic binary metal-nanoparticle arrays, comprising of Au and Fe, were fabricated on quartz substrates using nanosphere lithography and pulsed laser deposition technique. The dimension of the obtained triangular Au(Fe) particles was about 80 nm which was defined by the single-layer masks prepared by self-assembly of polystyrene nanospheres with radius R = 100 nm. The structural characterization of the particle arrays was investigated by atomic force microscopy. In the optical absorption spectra, the metal-nanoparticle arrays show a strong absorption peak of ~ 550 nm due to the surface plasmon resonance of metal particles. The nonlinear optical properties of the nanoparticle arrays were determined using a single beam z-scan method at a wavelength of 532 nm with laser duration of 55 ps. By adding Fe, the resonant absorption of Au particles was quenched, and the figure of merit χ⁽³⁾/α (with χ⁽³⁾ being the third-order nonlinear susceptibility, α being the absorption coefficient) was obviously increased. The obtained maximum χ⁽³⁾/α is about 6.15 × 10^− 12 esu cm. The results show that periodic Au + Fe nanoparticle arrays exhibit a large nonlinear optical property with fast response.     

Organic and inorganic hybrid film with second-order nonlinear optical and pyroelectric properties

An organic and inorganic hybrid material was prepared from a nonlinear optically active imidazole derivative 4-(nitrophenyl)-2,4-Bis-(4,4′-[N,N-bis-(2-hydroxyethyl)aminophenyl]) imidazole and metal alkoxide of Nb(V) via sol-gel process. The second-order nonlinear optical and pyroelectric properties of the hybrid film were investigated in terms of the second harmonic generation (SHG) and pyroelectric coefficient measurement. The SHG coefficient d₃₃ was found to be 29.3 pm/V at the fundamental wavelength of 1064 nm and the pyroelectric coefficient P was found to be 1.47 × 10^− 6 C/cm² K.     

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.     

Synthesis and NLO properties of hybrid inorganic-organic films containing thiophene ring

A family of second-order nonlinear optical sol-gel films with a pendent thiophene chromophore has been developed. The key step in preparation these hybrids was the syntheses of alkoxysilane dye containing thiophene ring, which was accomplished by utilizing the urethane forming reaction. Molecular structural characterization for the resultant was achieved by FTIR, ¹H NMR and UV-Visible spectra. The microscopic optical nonlinearity of the thiophene chromophore was evaluated to be 7646 × 10^− 30 esu D by solvatochromic method and second harmonic coefficients (d₃₃) of the hybrid film was also calculated to be 41.2 pm/V by second harmonic generation (SHG) measurements, respectively. Furthermore, the stability of optical nonlinearity in poled film was also investigated through a depoling experiment.     

Nonlinear optical response of silica doped with copper nanoclusters under 1064 nm laser excitation

Metal nanocluster composite glass was formed by Cu ion implantation into silica using metal vapor vacuum arc (MEVVA) ion source. The microstructural properties of the nanoclusters were analyzed by optical absorption spectra and transmission electron microscopy (TEM). Third-order nonlinear optical properties of the nanoclusters were measured at 1064 nm excitations using Z-scan technique. The nonlinear refraction index, nonlinear absorption coefficient, and the real and imaginary parts of the third-order nonlinear susceptibility were deduced. The mechanisms responsible for the nonlinear response were discussed. Third-order nonlinear susceptibility χ⁽³⁾ of this kind of sample was determined to be (4.2 ± 1.0) × 10⁻⁸ esu.     

Linear and nonlinear optical properties of plasma-enhanced chemical-vapour deposition grown silicon nanocrystals

We provide a systematic study on the linear and nonlinear optical properties of silicon nanocrystals (Si-nc) grown by plasma-enhanced chemical vapour deposition (PECVD). Linear optical properties, namely absorption, emission and refractive indices are reported. The sign and magnitude of both real and imaginary parts of third-order nonlinear susceptibility X(³) of Si-nc are measured by the Z-scan method. Closed aperture Z-scan reveals a positive nonlinearity for all the samples. From the open aperture measurements, nonlinear absorption coefficients are evaluated and attributed to two-photon absorption. Absolute values of X(³) are in the order of 10^-9 esu and show systematic correlation with the Si-nc size, due to quantum confinement related effects. A correlation has been made between X(³), nanocrystalline size, linear refractive index and optical band gap.     

Linear and nonlinear optical properties of RF sputtered (Pb,La)(Zr,Ti)O<Subscript>3</Subscript> ferroelectric thin films

Linear and nonlinear optical properties of (Pb,La)(Zr,Ti)O₃ (PLZT) ferroelectric thin films were presented in this paper. The PLZT ferroelectric thin films have been in situ grown on quartz substrates by radio-frequency (RF) magnetron sputtering at 650 °C. Their crystalline structure and surface morphologies were examined by X-ray diffraction and atomic force microscopy, respectively. It can be found that the PLZT thin films exhibit well-crystallized perovskite structure and good surface morphology. The fundamental optical constants (the band gap energy, linear refractive index, and linear absorption coefficient) were obtained through the optical transmittance measurements. A Z-scan technique was used to investigate the optical nonlinearity of the PLZT thin films on quartz substrates. The films display the strong third-order nonlinear optical effect. A large and negative nonlinear refractive index n ₂ is determined to be 1.21 × 10⁻⁶ esu for the PLZT thin films. All results show that the PLZT ferroelectric thin films have potential applications in optical limiting, switching, and modulated-type optical devices.     

Optical bistability for ZnO–Nb2O5–TeO2 glasses

We examined the optical nonlinear properties of ZnO–Nb₂O₅–TeO₂. The absorption and Raman spectra were measured, the third-order nonlinear susceptibility was determined by degenerated four wave mixing technique. The magnitude of χ⁽³⁾ is about 1.0 × 10⁻¹² esu, larger than that of silica glasses, and the optical bistability was observed in a Fabry–Perot cavity.