Order Nonlinear Optical Susceptibility Research Articles

Third harmonic generation in undoped and X doped ZnO films (X: Ce, F, Er, Al, Sn) deposited by spray pyrolysis

There is a current interest in research of wide band gap semiconductor materials for the purposes of third order nonlinear optical properties in view of optoelectronics applications. Materials for nonlinear optics should present important changes of nonlinear intensity, dependence on changes of nonlinear refractive index, short response time, and weak absorption losses. We report the results of the third order nonlinear optical susceptibilities of undoped and doped (cerium, fluorine, erbium, aluminum, and tin) zinc oxide films using the third harmonic generation technique at 1064 nm wavelength region in picoseconds regime. Thin films were grown on glass substrate by the spray pyrolysis technique at different temperatures of substrates and characterized by using the x-ray diffraction, scanning electron microscope, transmission, and photoluminescence. A strong third harmonic signal was obtained from the studied films with a good crystallinity and roughness. We have found that at high conductivity, there is a big conversion of the third harmonic signal at different dopants and at an appropriate concentration. We might say that the morphology and the crystalline quality of the films are the main factors for this high conversion.

Third order nonlinear susceptibility of InN at near band-gap wavelengths

The authors report room-temperature measurements of the third order nonlinear susceptibility modulus ∣χ(3)∣ of thick (∼600nm) InN layers. Transmission measurements provide a room-temperature value for the optical band gap of the samples slightly above 1500nm. Third order nonlinear optical susceptibility has been measured using degenerate four wave mixing experiments at wavelengths near and above band gap. ∣χ(3)∣ values of (4.2–10)×10−10esu were measured at this wavelength range. The associated relaxation time of the generated population grating at 1500nm was measured. The obtained value of 4.8ps is consistent with a nonradiative recombination mechanism.

Influence of the central metal atom on the nonlinear optical properties of MPcs solutions and thin films

Third order nonlinear optical susceptibility ( χ 〈3〉) of metallophthalocyanines (MPcs, where M = Co, Cu, Zn, Mg) thin films and solutions was investigated by standard backward degenerate four wave mixing (DFWM) method at 532 nm. Third harmonic generation (THG) measurement at 1064 nm performed on MPcs thin films is also discussed. MPcs thin films were grown by conventional thermal evaporation in high vacuum and solution were dissolved in tetrahydrofuran (THF), in which the studied materials are soluble. In the case of microscopic nonlinearity, we calculated the second order hyperpolarizability ( γ) for MPcs solutions. We found that the χ 〈3〉 and the γ values are affected by the nature of the central metal atom. We also found that the χ DFWM 〈 3 〉 value is larger than that measured via THG experiment. The variation in χ 〈3〉 values occurs due to the different resonance contributions.

Thermal and optical properties of zinc halotellurite glasses

Zinc halotellurite glasses were studied with respect to the glass transition, softening temperature, thermal expansion, optical energy gap, Urbach energy, density, molar volume, refractive index, polarizability, molar refraction and third order non-linear optical susceptibility. Thermal characteristic were determined using a dilatometry. The optical absorption in the wavelength range (300–3200 nm) was measured. From the absorption edge studies, the values of optical band gap (Eopt) and Urbach energy (ΔE) have been evaluated. Optical parameters viz., color dispersion, dispersion energy, Ed, average oscillator energy, E0, and third order non-linear optical susceptibility values are estimated from measuring the refractive index at different wavelength. Results obtained are discussed in terms of the glass structure.

ポリメチルメタクリレート／ターシャリブチルバナジルフタロシアニン複合膜の光双安定特性の入力光強度依存性

After organic gas treatment for 25 hrs in 1,2-Dichloroethane vapor, the third order nonlinear susceptibility of PMMA/Tertiary-butyl Vanadylphthalocyanine [(t-Bu)nVOPc] composite film was observed to increase markedly because the phase morphology of PMMA/(t-Bu)nVOPc composite film changed from Phase I to II. A waveguide was prepared with a triangular prism and PMMA/ (t-Bu)nVOPc composite film treated for 25 hrs in organic gas. When irradiating the waveguide with input laser power, the output power was recognized as having optical bistability. Moreover, the input laser power dependences of optical bistability were measured using the waveguide. Their optical bistability had a higher stability and sensitivity than that of the optical bistability reported previously and excellent reproducibility, which meant it was not necessary to write the error bars. However, in the input laser power dependences of optical bistability, the on-off switching position shifts according to the input laser power intensity. This indicates that by changing the input laser power intensity, the thickness of the PMMA/(t-Bu)nVOPc composite film increases due to the heat occurring when laser light is irradiated onto the composite film, leading to a marked enhancement in the third order nonlinear optical susceptibility (χ(3)), and a subsequent increase in the nonlinear optical refractive index of the PMMA/(t-Bu)nVOPc composite film, linked to an enhanced χ(3) value. Therefore, the increase in the χ(3) value is closely related to the changing switch on-off position, according to the input laser power intensity.

Linear electro-optical behavior of hybrid nanocomposites based on silicon carbide nanocrystals and polymer matrices

An electro-optical activity has been recently reported for hybrid nanocomposite thin films where inorganic silicon carbide nanocrystals $(\mathrm{ncSiC})$ are incorporated into polymer matrices. The role of the interface $\mathrm{SiC}$ polymer is suggested as the origin of the observed second order nonlinear optical susceptibility in the hybrid materials based on poly-(methylmethacrylate) (PMMA) or poly-($N$-vinylcarbazole) matrices. In this work, we report an analysis of the electro-optical response of this hybrid system as a function of the $\mathrm{ncSiC}$ content and surface state in order to precise the interface effect in the observed phenomenon. Two specific $\mathrm{ncSiC}$ samples with similar morphology and different surface states are incorporated in the PMMA matrix. The effective Pockels parameters of the corresponding hybrid nanocomposites have been estimated up to $7.59\ifmmode\pm\else\textpm\fi{}0.74\phantom{\rule{0.3em}{0ex}}\mathrm{pm}∕\mathrm{V}$ ($1\phantom{\rule{0.3em}{0ex}}\mathrm{wt}.\phantom{\rule{0.2em}{0ex}}%$ of $\mathrm{ncSiC}$ in the matrix). The interfacial region $\mathrm{ncSiC}$ polymer is found to play the main role in the observed effect. Particularly, the electronic defects on the $\mathrm{ncSiC}$ nanocrystal surface modify the interfacial electrical interactions between the two components. The results are interpreted and discussed on the basis of the strong influence of these active centers in the interfacial region at the nanoscale, which are found to monitor the local hyperpolarizabilities and the macroscopic nonlinear optical susceptibilities. This approach allows us to complete the description and understanding of the electro-optical response in the hybrid $\mathrm{SiC}$/polymer systems.

Spectral dependence of third order nonlinear optical susceptibility of zinc phthalocyanine

Wavelength dependence of saturable absorption (SA) and reverse saturable absorption (RSA) of zinc phthalocyanine was studied using 10Hz, 8ns pulses from a tunable laser, in the wavelength range of 520–686nm, which includes the rising edge of the Q band in the electronic absorption spectrum. The nonlinear response is wavelength dependent and switching from RSA to SA has been observed as the excitation wavelength changes from the low absorption window region to higher absorption regime near the Q band. The SA again changes back to RSA when we further move over to the infrared region. Values of the imaginary part of third order susceptibility are calculated for various wavelengths in this range. This study is important in identifying the spectral range over which the nonlinear material acts as RSA based optical limiter.

Langmuir-Blodgett Films of Novel Diacetylene-Containing Polymers with High Second Order Nonlinear Optical Susceptibility

ABSTRACT Langmuir-Blodgett films of four polymers containing benzoate and cinnamate main chains and Disperse Red 19 in the side chains were prepared and characterized by means of BAM and AFM. The poly(para-benzoate) and poly(para-cinnamate) gave LB films with much higher ordered textures than the respective meta-polymers. The para-polymers apparently possess self-assembly capacity, and this is thought to be the cause of their high second order nonlinear optical susceptibility. The X-type films of the para-polymers showed second order nonlinear optical responses, suggesting that the para-polymers form self organized membranes with the chromophores orientated to the direction perpendicular to the substrate.

Surface Enhanced Second Harmonic Generation from Macrocycle, Catenane, and Rotaxane Thin Films: Experiments and Theory

Surface enhanced second harmonic generation (SE SHG) experiments on molecular structures, macrocycles, catenanes, and rotaxanes, deposited as monolayers and multilayers by vacuum sublimation on silver, are reported. The measurements show that the molecules form ordered thin films, where the highest degree of order is observed in the case of macrocycle monolayers and the lowest in the case of rotaxane multilayers. The second harmonic generation activity is interpreted in terms of electric field induced second harmonic (EFISH) generation where the electric field is created by the substrate silver atoms. The measured second order nonlinear optical susceptibility for a rotaxane thin film is compared with that obtained by considering only EFISH contribution to SHG intensity. The electric field on the surface of a silver layer is calculated by using the Delphi4 program for structures obtained with TINKER molecular mechanics/dynamics simulations. An excellent agreement is observed between the calculated and the measured SHG susceptibilities.

Second-order nonlinear optical properties and polar order relaxation dynamics in a cyano-chromophore grafted polyurethane polymer

The all-optical recording of a microscopic second-order nonlinear susceptibility in a new azo dye pendant polyurethane polymer is investigated. An experimental configuration which permits self-phase matched was used. The peak value of the phase-matched light-induced second order nonlinear optical susceptibility χ(2) measured at 1.06μm reaches 62pm/V at room temperature, which corresponds to a molecular orientation ratio of 30%. Temporal stability of the induced polar order measured by second harmonic generation revealed a reduced decay rate of the χ(2) value in comparison to Disperse Red 1 pendant poly(methyl methacrylate).

Optimization of Intersubband Optical Nonlinearities in Continually Graded AlGaN Quantum Well Structures

A method is proposed for finding optimal AlGaN-based quantum well profiles with respect to specified intersubband optical properties, e.g. nonlinear optical susceptibilities at resonance. It is based on applying the isospectral transformations (supersymmetric and coordinate transform) to an initial Hamiltonian in order to generate a family of parameters of controlled potentials, accompanied by position-dependent effective mass. By varying those control parameters, one call change the values of dipole matrix elements relevant for a particular effect, while energy levels, once obtained in the initial potential, remain unchanged. The internal electrostatic field, originating from piezoelectric and spontaneous polarization in the nitride alloy, has been taken into account. The use of the method is illustrated by maximizing second order nonlinear optical susceptibilities at wavelengths in the near infrared spectral range, and optimal smooth structures are eventually discretized to make their fabrication easier.

Second Molecular Hyperpolarizability of Mixed Transition Metal, Non-Metal Clusters

The real and imaginary parts of third order nonlinear optical susceptibilities (χ (3)) of 10−4M solutions of [{Fe2(CO)6}(μ 3-Y3P){CpCr(CO)2}] (Y=S (1) or Se (2)) and the well known precursor clusters [Fe3(CO)9(μ 3-Y)2] (Y=S (3) or Se (4)) in toluene were measured using Z-scan and ARINS techniques respectively. Compounds 1 and 2 possess nearly three times the γ R values of their corresponding precursor compounds, 3 and 4. The results suggest a rich potential of mixed-metal, mixed-nonmetal class of clusters as materials exhibiting large nonlinearity.

Third order nonlinear optical susceptibility of Cu:Al2O3 nanocomposites: From spherical nanoparticles to the percolation threshold

The third order optical susceptibility of metal-dielectric nanocomposite films (Cu:Al2O3) has been determined by degenerate four wave mixing. The films have been synthesized by alternate pulsed laser deposition and consisted of Cu nanoparticles in an amorphous Al2O3 matrix. They have metal volume fractions, p, ranging from 0.07 to 0.45, and morphologies that range from spherical particles (diameter, φ∼2 nm) to a random network when close to the percolation threshold. In nanocomposites containing isolated oblate spheroids (p⩽0.17), the optical response at wavelengths close to that of the surface plasmon resonance (SPR) can be described in the frame of the Maxwell-Garnett effective medium theory. Above the particle coalescence threshold, in nanocomposites with higher Cu content (p⩾0.2), both the linear absorption in the near-infrared and the third order nonlinear optical susceptibility at the SPR are greatly enhanced, the latter achieving values as high as 1.8×10−7 esu. These results are discussed in terms of multipolar interactions among particles and giant local resonance effects that appear as a consequence of the particle coalescence and the increase in size of the nanocrystals.

Purely magnetization-induced second-harmonic generation in thin garnet films

Optical second-harmonic generation (SHG) of purely magnetic origin has been observed in thin films of Lu3-χ Biχ Fe5-y Gay O12 grown on (100) oriented gadolinium gallium garnet (GGG) substrates for the purpose of magneto-optical imaging. The films have in-plane magnetization, and when studied in transmission at normal incidence all relevant elements of the crystallographic part of the second order non-linear optical susceptibility tensor vanish identically, while a magnetization-induced contribution remains. The observed rotational anisotropy SHG signal in a transverse magnetic field is demonstrated to be indeed of purely magnetic origin, and can be switched off by applying a polar magnetic field.

An effective-medium approach to the optical properties of heterogeneous materials with nonlinear properties

We have derived an analytic approach, based on the hypothesis of the effective-medium theory, to evaluate the effective dielectric magnitudes, including the effective third order nonlinear optical susceptibility α(χ(3)), of a heterogeneous two-component medium in which one of the components (the host matrix or the embedded particle respectively) presents nonlinear behaviour. Our formulation allows us to solve the full nonlinear problem in the whole range of concentrations without treating the nonlinear effects as a small perturbation to the linear behaviour. Therefore, it can be considered as an upper limit of the commonly used low-field nonlinear approximations for heterogeneous materials. Under certain conditions, these composites can exhibit a bistable regime that the present theory properly describes in wide ranges of the concentration, shape, wavelength, dielectric contants and intrinsic nonlinear optical susceptibility of the nonlinear component as well as in terms of the intensity of the external electric field. The present approach has been used to calculate the nonlinear optical response of Cu—Al2O3 nanocomposites.

塩化カリウム（１００）基板上に作製されたバナジルフタロシアニン薄膜の形態と非線形光学強度の膜厚依存性

Vanadyl-phthalocyanine (VOPc) thin films were fabricated on KC1 (100) substrate by a molecular beam epitaxy. The morphologies of VOPc thin films fabricated under different preparing conditions were investigated by using Vis/ UV spectra, AFM images and the third order nonlinear optical properties measured with Maker fringe. The morphology of VOPc thin film on a KC1 substrate has three types. The first type has VOPc molecules tilted epitaxially on KC1 substrate, the second type has pseudomorphic VOPc layers on the epitaxial layer, and the third type is the bulk VOPc crystals deposited on the pseudomorphic layer. The third order nonlinear optical susceptibility estimated from a maximum third harmonic intensity of VOPc thin film measured by Maker fringe is about 10-9 esu. This is a practical value requested for the application to optical devices such as optical switching and memory.

Diacetylene-containing polymers. XIII. Poly(hexa-2,4-diynylene-l,6-dioxydicinnamates) containing an azo dye, Disperse Red 19

In order to obtain polymers having high second order nonlinear optical susceptibility, a series of novel polymers that contain a diacetylene group in the main chains and a polar chromophore (Disperse Red 19) were synthesized and characterized. These poly(hexa-2,4-diynylene-1,6-dioxydicinnamates) undergo crystallization in dimethylformamide solution, and the polymer crystals were only soluble in N-methylpyrrolidinone. The polymer films could be cross-linked by irradiation of UV light to give completely insoluble materials. Preliminary experiments on second order nonlinear properties of these polymers showed that the para-polymer was found to have nonlinear optical coefficients about five times greater than the meta-polymer.

Non-linear optical phenomena in the large-sized nanocrystallites

Photoinduced second harmonic generation (PISHG) in SiC nanocrystallites (with sizes ranging from 10 to 30 nm) incorporated into an oligoetheracrylate photopolymer matrix was studied using an experimental photoinducing non-linear optical technique and ab initio molecular dynamics simulations. PISHG measurements were made using a pulse YAG:Nd laser ( λ=1.06 μm ; duration time varying from 4 to 850 ps, laser power about 14 MW) as the probing beam and a nitrogen pulse laser ( P=25 MW; λ=0.377 μm ) as the pumping beam synchronized with a probing beam. We found that with an increase in the nitrogen laser power, the PISHG output signal increased and achieved its maximum value at nitrogen laser photon flux of about 2.6 GW/ cm 2 . Maximum output PISHG signals were observed for parallel polarization of the photoinducing and probing light beams. The second order non-linear optical susceptibility observed at the maximum PISHG was about 1.2 pm/V. The PISHG signals increased as the sample temperature decreased. This increase became marked when the temperature fell below 30 K. Time-dependent probe-pump measurements showed the existence of a PISHG maximum at a time delay of about 20–25 ps. As a result of total energy structure optimization, a good correlation between the size dimensions and the degree of hexagonality within the nanocrystallites was observed. An increase in the degree of hexagonality was also found to cause an increase in the PISHG signal. At a temperature of about 4.2 K, and with a time delay of 25 ps, the maximum PISHG was observed for a degree of hexagonality of approximately 0.76. Our calculations suggest that hexagonal substructures play a key role in the photoinduced effects observed. Several discrepancies between theoretical and experimental data may be caused by specimen in-homogeneity which is usually present in such kinds of materials.

Linear optical properties of niobium-based tellurite glasses

10·Na 2O– x·Nb 2O 5–(90− x)·TeO 2 ( x=0, 5, 10 and 20) glasses have been prepared and some of their physical and optical properties are investigated. The refractive index variation with wavelength is measured using a novel technique, white light interferometry. Optical band gaps and Urbach energies are estimated from the optical absorption spectra. Optical parameters viz., dispersion energy, average oscillator energy, Abbe's number and third order nonlinear susceptibility values are estimated from the dispersion of the refractive index. Respective refractive index and estimated third order nonlinear optical susceptibility values are larger than for the tellurite glasses reported earlier. Relatively large refractive index values obtained for the present glasses are attributed to the hyperpolarisability of the Nb–O bands. The present study of the optical band gap and dispersion energies of these glasses suggests the decrease of covalency of the glass with the increase of niobium (Nb) content.

Dielectric properties of I-III-VI2-type chalcopyrite semiconductors

Dielectric properties of I-III-${\mathrm{VI}}_{2}$-type ternary chalcopyrite semiconductors, including linear and second order nonlinear optical susceptibilities at 10.6 \ensuremath{\mu}m, have been quantitatively studied from the chemical bond viewpoint. Contributions from each type of constituent chemical bond, i.e., I $\char22{}$ VI and III $\char22{}$ VI bonds, to the total linear and nonlinear optical properties of these compounds at 10.6 \ensuremath{\mu}m have been theoretically determined. The chemical bond method quantitatively expresses the trends in the dielectric properties of these compounds, which is helpful for carrying out modeling of their properties.