Third-order Nonlinear Optical Effects Research Articles

The synthesis, structure and third-order nonlinear optical effect of a new 2D cluster polymer based on a [WS4Cu4]2+ SBU and 1,2-di(pyridin-4-yl)ethane

The self-assembly reaction of a multinodal preformed cluster with 1,2-di(pyridin-4-yl)ethane as the organic ligand afforded the 2D cluster polymer (1), {[(WS4Cu4)I2(dpe)2](DMF)4}n. There is a cavity between each two nearby dpe ligands in 1. The [WS4Cu4]2+ units are fixed by I− ions, which is attributed to the multinodal feature of the W–S–Cu secondary building units, and therefore, the cavities in 1 are settled. The NLO properties show that 1 exhibits an optical self-focusing behavior and reverse saturable absorption effects. This work provides us with useful clues to further explore the 2D W–Cu–S-based cluster polymer with cavities.

Plasmon-assisted enhancement of third-order nonlinear optical effects in core (shell) nanoparticles

We study resonant self-action effects of light in plasmonic γ-Fe2O3 (Au) core (shell) nanoparticles (NPs) in a polymer matrix by the spectroscopic Z-scan technique. Plasmon-assisted enhancement of the local optical field in NPs results in the appearance of saturable absorption, as well as in the amplification of nonlinear refraction by more than an order of magnitude compared with nonresonant conditions.

Excimer laser deposited CuO and Cu2O films with third-order optical nonlinearities by femtosecond z-scan measurement

By controlling the oxygen pressure, single-phase CuO and Cu2O thin films have been obtained on quartz substrates using a pulsed laser deposition technique. The structure properties and linear optical absorption of the films were characterized by X-ray diffraction and UV–VIS spectroscopy. By performing z-scan measurements using a femtosecond laser (800 nm, 50 fs), the real and imaginary parts of the third-order nonlinear susceptibility, Re χ (3) and Im χ (3), of the films were determined. Both CuO and Cu2O films exhibited large optical nonlinearities, which is comparable to those in some representative semiconductor films such as ZnO and GaN films using femtosecond laser excitation. Compared with Cu2O films, the CuO films showed larger third-order nonlinear optical effects under off-resonance excitation. Furthermore, the mechanisms of the optical nonlinearities in CuO and Cu2O films are explained in the main text. It was suggested that the reasons of the difference in their nonlinear refractive effects may be related to the different electronic structure in CuO and Cu2O materials.

Ultafast organic nonlinear optical molecules and the realization of mesoscopic photonic devices

In the twentieth century, revolutionary changes took place in the human society and people’s life-style due to the improvement of the optoelectronic information technology based on the second-order nonlinear optical effects, such as the electro-optic effect, the second harmonic generation (SHG), and so on. Along with the rapid development of light information technology, new principles and methods of nonlinear optics are needed, and the third-order nonlinear optical effects attract great attention. The research progress of nonlinear optics is reviewed in this article. Our research work on the third-order nonlinear optical materials, ultrafast and low-power organic all-optical photonic crystal switching are introduced.

Photoinduced transient Faraday rotation in NiO

A non-thermal ultrafast magneto-optical response of antiferromagnetic NiO to irradiation with an intense optical pulse was observed. With temporally overlapping pump and probe pulses, the circularly polarized pump pulse induced rotation of the linear polarization of the probe pulse along with two-photon absorption and cross-phase modulation. The sign of the rotation of the linear polarization reversed with the reversal of the pump helicity. This non-resonant phenomenon is described as a third-order nonlinear optical effect and is ascribed to an inverse Faraday effect: photoinduced magnetization.

Quantitative myelin imaging with coherent anti-Stokes Raman scattering microscopy: alleviating the excitation polarization dependence with circularly polarized laser beams

The use of coherent anti-Stokes Raman scattering microscopy tuned to the lipid vibration for quantitative myelin imaging suffers from the excitation polarization dependence of this third-order nonlinear optical effect. The contrast obtained depends on the orientation of the myelin membrane, which in turn affects the morphometric parameters that can be extracted with image analysis. We show how circularly polarized laser beams can be used to avoid this complication, leading to images free of excitation polarization dependence. The technique promises to be optimal for in vivo imaging and the resulting images can be used for coherent anti-Stokes Raman scattering optical histology on native state tissue.

Nonlinear Optical Response of Chloroaluminiumphthalocyanine Encapsulated by Silica Core−Shell Particles

We report for the first time on the synthesis of core-shell particles containing chloroaluminiumphthalocyanine (ClAlPc) prepared using a sol-gel technique. These particles have the dye molecules at the core, encapsulated by silica shell. The mean size of the particle is determined from HRTEM studies and is found to be approximately 0.08 microm. The surface and bulk compositions of the core-shell particles are studied by XPS and EDAX measurements, respectively. Time-resolved fluorescent measurements indicate a decrease in fluorescence lifetime for the core-shell particles as compared to that of bare dye dissolved in ethanol. This is analyzed on the basis of available theoretical models. Third-order nonlinear optical effects are investigated by the Z-scan technique using 8 ns pulses at a wavelength of 532 nm from a frequency-doubled Nd:YAG laser. The analysis indicates that both singlet and triplet excited-state absorption contribute to nonlinear absorption.

Hybrid organic-dielectric thin film stacks for nonlinear optical applications

We propose an optical switching device that utilizes the third-order nonlinear optical effect in an organic material embedded into a superprism photonic crystal structure. A convenient way for the realization of the photonic crystal is using a multilayer thin film stack made of dielectrics. Following this approach, we face the challenge of building hybrid stacks containing both inorganic dielectric as well as organic materials. We evaluate strategies for the design and fabrication of hybrid thin film stacks to avoid the development of thin film cracking during the fabrication of hybrid PS-Ta 2O 5 (polystyrene-tantala) and PMMA-Ta 2O 5 (poly(methyl methacrylate)-tantala) stacks on glass substrates. Crack-free hybrid PS-Ta 2O 5 as well as PS-SiO 2 (polystyrene-silicon dioxide) and PMMA-SiO 2 (poly(methyl methacrylate)-silicon dioxide) samples on glass substrates were fabricated.

Linear and nonlinear optical properties of (Pb,La)(Zr,Ti)O3 ferroelectric thin films grown by radio-frequency magnetron sputtering

Linear and nonlinear optical properties of lanthanum-modified lead zirconate titanate (Pb0.92La0.08)(Zr0.65Ti0.35)O3 (PLZT 8/65/35) ferroelectric thin films are presented in this paper. The PLZT ferroelectric thin films were grown on quartz substrates by radio-frequency magnetron sputtering at 650 °C. Their crystalline structure and surface morphologies were examined by x-ray diffraction and atomic force microscopy, respectively. It was 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 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 a strong third-order nonlinear optical effect. A large and negative nonlinear refractive index n2 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 nonlinear optical devices.

Dependence of third-order nonlinear optical effect on refractive index in barium (Li) aluminum (Ga or Si) borate ternary glasses produced by new pulling down technique

Ternary glasses of barium (Li-substituted) aluminum (Ga- or Si-substituted) borate were solidified by new technique using conventional Floating-zone Pulling Down system. It was difficult to grow single crystalline materials in this system. However, solidification of glasses was easy. Refractive indexes of these glasses were 1.5–1.7. Third-order nonlinear optical effects, χ(3), were larger than that of standard SiO2 glass at 355nm. Despite small refractive indexes as oxide glasses, large χ(3) were obtained.

Ordered adsorption of coagulation factor XII on negatively charged polymer surfaces probed by sum frequency generation vibrational spectroscopy

Electrostatic interactions between negatively charged polymer surfaces and factor XII (FXII), a blood coagulation factor, were investigated by sum frequency generation (SFG) vibrational spectroscopy, supplemented by several analytical techniques including attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), quartz crystal microbalance (QCM), zeta-potential measurement, and chromogenic assay. A series of sulfonated polystyrenes (sPS) with different sulfonation levels were synthesized as model surfaces with different surface charge densities. SFG spectra collected from FXII adsorbed onto PS and sPS surfaces with different surface charge densities showed remarkable differences in spectral features and especially in spectral intensity. Chromogenic assay experiments showed that highly charged sPS surfaces induced FXII autoactivation. ATR-FTIR and QCM results indicated that adsorption amounts on the PS and sPS surfaces were similar even though the surface charge densities were different. No significant conformational change was observed from FXII adsorbed onto surfaces studied. Using theoretical calculations, the possible contribution from the third-order nonlinear optical effect induced by the surface electric field was evaluated, and it was found to be unable to yield the SFG signal enhancement observed. Therefore it was concluded that the adsorbed FXII orientation and ordering were the main reasons for the remarkable SFG amide I signal increase on sPS surfaces. These investigations indicate that negatively charged surfaces facilitate or induce FXII autoactivation on the molecular level by imposing specific orientation and ordering on the adsorbed protein molecules.

Linear and nonlinear optical properties of RF sputtered (Pb,La)(Zr,Ti)O3 ferroelectric thin films

Linear and nonlinear optical properties of (Pb,La)(Zr,Ti)O-3 (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 degrees 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 x 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.

Synthesis and Z-scan measurements of third-order optical nonlinearity in push–pull molecules with dihydroxylethyl amino donor and nitro acceptor

Novel azo diol chromophores were synthesized through multi-step azo-coupling reaction and characterized by NMR, IR, and UV. The third-order NLO properties of the chromophores were investigated. The measurements of second hyperpolarizabilities were performed using single-beam Z-scan technique with picosecond laser pulses at 1064 nm in DMF solutions. Our results indicate that larger second hyperpolarizabilities γ can be readily obtained in such chromophores because of increase of molecular conjugation length and donor–acceptor conjugation path. Further enhancement of γ has been achieved via replacement of phenyl rings in the conjugated backbone by heteroaromatic spacers such as benzothiazole and pyrimidine rings. Therefore, it is very probable that the increase in the obtained γ values considerably arises from the conjugation path of the delocalized electrons for large third-order nonlinear optical effects.

Enhanced Third-Order Nonlinear Optical Properties in Dendrimer−Metal Nanocomposites

Nonlinear optical (NLO) and time-resolved fluorescence spectroscopic measurements of dendrimer-metal nanocomposites (DNCs) are reported. Third-order NLO effects were investigated by degenerate four-wave mixing (DFWM) measurements for DNCs and DNCs incorporated into thin polymeric films. The results show an enhancement of the third-order nonlinear susceptibility for the chromophore-functionalized dendrimer-metal nanocomposites. Investigations of the mechanism of the enhanced NLO effect suggested a strong contribution because of the metal's local field. These results show the potential usefulness of dendrimer-metal nanocomposites for nonlinear optical effects and biophotonic applications.

Synthesis and third-order optical nonlinearity in two-dimensional A-π-D-π-A carbazole-cored chromophores

Novel A-π-D-π-A carbazole-cored chromophores were synthesized and characterized by NMR, IR, UV techniques. The third-order NLO properties of the carbazole chromophores were investigated. The measurements of second-order hyperpolarizabilities were performed using single-beam Z-scan technique with picosecond laser pulses in DMF solutions. Our results indicate that larger second-order hyperpolarizabilities γ can be readily obtained in such carbazole chromophores because of increasing strength of withdrawing group and molecular conjugation length with two aromatic bridges in the two-dimensional conjugated system. Therefore, it is very probable that the increase in the obtained γ values considerably arises from the conjugation path of the delocalized electrons for large third-order nonlinear optical effects.

Magnetization-induced second- and third-harmonic generation in magnetic thin films and nanoparticles

The results of our recent experimental studies of magnetization-induced second- and third-order nonlinear optical effects in magnetic nanostructures are surveyed. Magnetization-induced variations of the intensity, the polarization state, and the relative phase of the second-harmonic wave are studied in magnetic nanogranular films, self-assembling films with garnet nanoparticles, thin magnetic metal films, and Langmuir-Blodgett films containing rare-earth ions. The nonlinear magneto-optical Kerr effect (NOMOKE) in second-harmonic generation (SHG) from thin magnetic and granular films is shown to exceed the linear magneto-optical Kerr effect by at least 1 order of magnitude. Magnetization-induced optical third-harmonic generation (THG) is observed in thin magnetic metal films and nanogranular films. The NOMOKE in THG from these magnetic nanostructures appears to be of the same order of magnitude as the second-order NOMOKE in SHG. The NOMOKE magnetic contrast in the THG intensity is up to ∼0.1 in Co_xAg(_1−x) nanogranular films. For the THG wave, the magnetization-induced rotation of polarization is up to 10° in thin Fe(110) films, and the relative phase shift is up to 70° in thin Co films. The studies of the magnetization-induced quadratic and cubic nonlinear-optical effects show the interconnection between the magnetic, structural, and magneto-optical properties of magnetic nanomaterials.

Investigation of the Soret coefficient in magnetic fluids using the Z-scan technique

The generalized thermal lens model formalism, which includes on it the thermodiffusion phenomenon, is used to determine the Soret coefficient ( S T) of a cationic surfacted ferrofluid. The single-beam Z-scan experiment is employed to obtain both the magnitude and sign of S T. Besides S T, the method allows the determination of the parameter ∂ n / ∂ I , where n and I are the sample index of refraction and the incident laser beam intensity on the sample. This parameter accounts for the third-order nonlinear optical effects which yield in the sample an instantaneous modification of the index of refraction, proportional to the intensity of the local light.

Enhanced optical nonlinearity near the photonic bandgap edges of a cholesteric liquid crystal

The third-order Kerr nonlinear optical effect of a one-dimensional photonic bandgap structure of a cholesteric liquid crystal is investigated. In a femtosecond nonlinear transmission measurement, nonlinear optical changes in the bandgap edges are observed. From analysis of the dispersion relation, Kerr nonlinear coefficients of nematics, forming the cholesteric liquid crystal, are found to be enhanced by 1-2 orders of magnitude through the photonic bandgap structure.

Optical non-linearity in Disperse Red 1 dye-doped sol–gel

Abstract A third-order non-linear optical effect, the optical Kerr effect, was studied in DR1-doped sol–gel using the Z-scan method which allows studying both processes of non-linear absorption and refraction. The materials under study are sol–gel substrates, amorphous silica glasses doped by the azo-dye Disperse Red 1. Modifying the conditions of the sol–gel synthesis, in particular the pH of the catalytic medium, enabled us to vary the morphology of the sol–gel substrate. Non-linear effects of various amplitudes were observed in sol–gel substrates of various porosities, involving different non-linear mechanisms.

THEORETICAL STUDIES ON NONLINEAR INTERACTION BETWEEN LASER AND BIO-MOLECULES IN OPTICAL TOMOGRAPHY

The nonlinear interaction between laser and bio-molecule has been studied by the theory of molecular nonlinear polarization. The expressions of operators of Hamiltonian, the moment of dipole and the electric susceptibility with different orders have been evaluated. The contributions of electrons and nuclei to the molecular polarization have been analyzed. A SHG tomography induced by third-order nonlinear optical effect has also been proposed.