新型偶氮苯衍生物的三阶非线性光学特性

本文以30 ps的脉冲激光为激发光源,用Z扫描技术研究了偶氮苯类材料4-羟基-4’-羧基偶氮苯(BN)和N-(3,4,5-辛氧基苯基)-N’-4-[(4-羟基苯)偶氮苯]1,3,4-恶二唑(AOB-t8)及金属复合物(Au/AOB-t8)的三阶非线性光学性质,并从理论上进行了分析和计算.结果表明,AOB-t8的三阶非线性极化率是BN的1.38倍,其非线性光学效应的增大是由共轭链增长、大π键增多引起的.结果同时给出,AOB-t8的三阶非线性极化率是其与金纳米颗粒复合物的4.7倍,这种与金属复合产生的非线性光学效应的减弱是金属引入的局域场效应与有机分子大π键作用之间相互抵消导致的.     

Third-order nonlinear optical properties of multiwalled carbon nanotubes modified by CdS nanoparticles

CdS nanoparticles were coated on the side wall of multiwalled carbon nanotubes (MWCNTs) by a wet chemical synthesis approach via noncovalent functionalization of MWCNTs with poly(diallyldimethylammonium chloride) (PDDA). The as-prepared material was characterized by X-ray diffraction (XRD), UV–vis absorption, fluorescence and transmission electron microscopy (TEM). The results indicated that CdS nanoparticles were uniformly coated on the surface of MWCNTs. Third-order optical nonlinearity of the as-prepared material was studied with the Z-scan technique with picosecond laser pulses at 532 nm. The Z-scan curve revealed that CdS nanoparticle-modified MWCNTs exhibited negative nonlinear refraction index and positive absorption coefficient. The real part and imaginary part of the third-order nonlinear susceptibility χ⁽³⁾ were calculated to be −4.9 × 10⁻¹² and 6.8 × 10⁻¹³ esu, respectively.     

三-α-(2,4-二甲基-3-戊氧基)溴硼亚酞菁的三阶非线性光学性质研究

应用Z扫描技术，在波长为532nm、脉宽为8ns条件下，对一种新型亚酞菁配合物三-α-(2,4-二甲基-3-戊氧基)溴硼亚酞菁的三阶非线性光学特性进行了研究，结果发现，该新化合物有较强的反饱和吸收(β=3.7×10^-10 m/W)效应和非线性自聚焦折射效应(n₂=7.2×10^-11esu)，其三阶非线性极化率χ⁽³⁾=1.1×10^-11esu.分析了溴硼亚酞菁配合物特殊的锥形分子结构和重原子溴的轴向配位等因素对其三阶非线性光学性质的重要影响. 关键词： 亚酞菁 Z扫描 三阶光学非线性     

Photophysical properties of pyridyloxy phthalocyanine encapsulated in nanoparticles

Two aluminum chloride phthalocyanines with pyridyloxy substitution at α/β positions were synthesized. Their structures were characterized by infrared spectroscopy, proton nuclear magnetic resonance as well as elemental analysis. Tetra-α(β)-(2-pyridyloxy) aluminum chloride phthalocyanines were encapsulated into a diblock copolymer methoxy-poly(ethylene glycol)-block-poly(L-lysine) through a cosolvent method. The morphologies and photophysical properties of phthalocyanines encapsulated in nanoparticles were studied by transmission electron microscope, ultraviolet-visible, and fluorescence spectroscopic methods. The photophysical properties of phthalocyanines encapsulated into nanoparticles exhibited substitution positions dependence. The phthalocyanines with substitution at α positions were found to be an excellent candidate for use as photosensitizers for treatment of cancer by photodynamic therapy.     

Interface effects on the nonlinear optical properties of thin films

The optical nonlinearity of low-dimension structures is studied in the self-effect case at a wavelength of 630 nm in a range of light intensities below 0.1 W/cm² by waveguide methods. Common tendencies in relationships between intensity of light and optical properties of multilayer structures and semiconductor-doped glass films are detected. It is shown that the state of interfaces determines the character of optical nonlinearity.     

Calculation of nonlinear waves guided by optical fibers with an inhomogeneous nonlinear core

A circular optical fiber consisting of an inhomogeneous nonlinear core bounded by a linear cladding medium is considered here. In this case, the calculation of the nonlinear modes is of practical importance because of the joint effects of nonlinearity and inhomogeneity on the field concentration and the achievable optical confinement. Numerical results indicate that the combination of this type of inhomogeneity along with the characteristics of nonlinearity may play a significant role towards the optical confinement in the core.     

Ultrafast third-order optical nonlinearity of several sandwich-type phthalocyaninato and porphyrinato europium complexes

The third-order optical nonlinearity of two sandwich-type phthalocyaninato and porphyrinato europium com- plexes, including double- and triple-deckers （Eu[Pc（OC5H11）8]2, Eu2（Pc）（TPP）2, Pc=phthalocyanine, TPP=5, 10, 15, 20- tetraphenylporphyrinate）, was investigated by using the femtosecond time-resolved optical Kerr gate method at 830 nm wavelength. Their second-order hyperpolarizability is estimated to be 0.74× 10^-30esu and 3.0× 10^-3esu respectively. This exhibits an evident enhancement in comparison with 0.47×10^-30esu for one-decker Eu（Pc）（acac） （acac=acetylacetonate）, which is also measured under the same conditions. The enhancement is attributed to the introduction of lanthanide metal to the large π-conjugated system, intermacrocycle interaction and two-photon resonance etc.     

Third-order nonlinear optical properties of thin sputtered gold films

Au films of thickness ranging between 5 and 52 nm were prepared by sputtering on quartz substrates and their third-order nonlinear optical response was investigated by Optical Kerr effect (OKE) and Z-scan techniques using 532 nm, 35 ps laser pulses. All prepared films were characterized by XRD, AFM and UV-VIS-NIR spectrophotometry while their third-order susceptibility χ⁽³⁾ was measured and found to be of the order of 10⁻⁹ esu. The real and imaginary parts of the third-order susceptibility were found in very good agreement with experimental results and theoretical predictions reported by Smith et al. [D.D. Smith, Y. Yoon, R.W. Boyd, Y.K. Cambell, L.A. Baker, R.M. Crooks, M. George, J. Appl. Phys. 86 (1999) 6200].     

Investigation of third-order nonlinear optical properties of conjugated benzodioxal derivatives

An investigation of third-order nonlinear optical characterization of newly synthesized conjugated benzodioxal derivatives has been done by using nanosecond Z-scan technique at 532 nm. The molecules demonstrate self-defocusing effect with intensity dependent refractive index (n₂) of the order of 10⁻¹⁴ cm²/W. The measured molecular TPA cross-section is ranging from 2.47 ×10⁻⁴⁷ cm⁴ s/photon to 6.00 cm⁴ s/photon. Their input-output curves indicate that there is a clear optical power limiting behavior with the limiting threshold in the range 125-181 μJ. The main factor to exhibit the observed nonlinearity in these molecules is the presence of charge donor and acceptor groups. The increased conjugation length increases the nonlinear refraction and increased electron density enhances the nonlinear absorption. The molecules exhibit good nonlinear optical properties, comparable to those of regular azoaromatic compounds. Therefore, the molecules investigated here are promising candidates for optical power limiting devices.     

Nonlinear optical properties in double-sided nonlinear media with Z-scan technique based on the Huygens——Fresnel principle

We present a theoretical model to analyse the propagation of a Gaussian laser beam through double-sided nonlinear media. This model is based on the Huygens--Fresnel diffraction integral method. This theoretical model is not only consistent with the cascade structure model for a small nonlinear phase-shift but also can be used for a large nonlinear phase-shift. It has been verified that it is suitable to characterize the double-sided nonlinear media compared with the cascade structure model. A good agreement between the experimental data and the results from the theoretical model is obtained. It will be useful for the design of multi-sided nonlinear materials.     

噻二唑衍生物分子的电子光谱与三阶非线性光学性质

含噻二唑环偶氮类芳香有机化合物具有良好的有机非线性光学性能.采用密度泛函理论B3LYP方法和6-311++G(d,p)基组对6个噻二唑衍生物分子进行结构优化与频率计算,运用含时密度泛函理论对其吸收光谱进行理论计算,采用有限场方法及自编程序计算其三阶非线性光学性质(NLO).结果表明,6个分子的吸收波长在361~383nm范围内,属于近紫外区.组成噻二唑衍生物分子的羟基苯环与噻二唑环均不共面,-CH3或Cl引入到羟基苯环的邻、间、对位后,其共面程度与三阶NLO系数γ均按邻、间、对位取代递减.同一位置,引入-CH3比引入Cl原子的三阶NLO系数γ大.因此,在羟基苯环的邻位引入较强的供电子基,可以设计成为良好的三阶非线性光学材料.     

Photophysical and nonlinear optical properties of zincphthalocyanines with peripheral substitutions

Photophysical and nonlinear optical properties of zinc phthalocyanines (ZnPc) bearing peripheral phenoxy substituents containing different functionalized groups were studied. Fluorescence spectra corresponding to the optical transition S₁ → S₀ are found to be appeared at 684 or 686.4 nm. Z-scan technique reveals large nonlinearities, where the absorptive and refractive effects are separately evaluated. Saturation absorption of ZnPc-1 was observed at 632.8 nm, with a very large nonlinear absorption coefficient β = −1.36 × 10⁻² cm/W. However a strong nonlinear refractive effect was found in all ZnPcs (1-4). Transmitted versus incident irradiance measurements carried out on ZnPc-1 and ZnPc-2, showed a very clear optical limiting behavior with irradiance thresholds around be 44 W/cm² and 90 W/cm² respectively.     

Study on the structure dependent ultrafast third-order optical nonlinearity of GeS2–In2S3 chalcogenide glasses

The results of the femtosecond time-resolved optical Kerr at 820 nm in GeS₂–In₂S₃ chalcogenide glasses indicate that the response time in GeS₂–In₂S₃ glasses is subpicosecond, which is predominantly due to the distortion of the electron cloud. The value of χ⁽³⁾ in 0.95GeS₂–0.05In₂S₃ glass is also as large as 2.7 × 10⁻¹³ esu, and it reduces with the addition of In₂S₃, which may be ascribed to the microstructure evolution of GeS₂–In₂S₃ glasses. It is deduced that the intrinsic [Ge(In)S₄] tetrahedral structure units that possess the high hyperpolarizability may do great contribution to the enhancement of third-order optical nonlinearity while [S₃Ge–GeS₃] ethane-like molecular units make no considerable contribution to that in femtosecond time scale. These GeS₂–In₂S₃ and GeS₂–In₂S₃-based chalcogenide glasses would be expected to be the promising materials for all-optical switching devices.     

碳纳米管/二硒化钼有机玻璃的非线性吸收、非线性散射和光限幅特性

MoSe₂的禁带宽度较窄（1.1–1.5 eV）,且具有可调谐的激子光电效应,这样使其在光致发光、光电晶体管、太阳能电池和光学非线性等方面具有潜在的应用价值.然而,纯的MoSe₂的光生电子空穴复合率较高,限制了其在某些光学领域中的应用.通过设计MoSe₂的复合材料,可以降低材料的光生电子空穴复合率,从而扩展其应用领域.首先,通过热溶剂法合成CNT/MoSe₂复合材料;然后,通过浇铸法将其分散在甲基丙烯酸甲酯（MMA）中制备成有机玻璃,其中MMA会聚合成聚甲基丙烯酸甲酯（PMMA）,并利用改进的Z-扫描技术首次对CNT/MoSe₂/PMMA有机玻璃的非线性吸收、非线性散射和光限幅特性进行了研究.研究表明,随着输入能量的变化,通过调节输入能量,CNT/MoSe₂/PMMA有机玻璃表现出饱和吸收（SA）和从SA到反饱和吸收的转变.结合材料特性及应用条件要求,可以得到CNT/MoSe₂/PMMA有机玻璃在光学设备,如光学限制器和锁模/调Q激光器等方向具有较好的应用前景.     

Nonlinear optical properties of an azobenzene polymer

The nonlinear optical properties of an azobenzene polymer azol2-MO were investigated by a Z-scan technique. The polymer was synthesized by assembling the liquid-crystalline polymer azol2 with methyl orange. The nonlinear refrac- tive index （1.39×10^-15 cm2/W） and the nonlinear absorption coefficient （0.11 cm/GW） of azol2-MO were determined with 532-nm picosecond laser pulses at the irradiance of 92.40 GW/cm2. When compared to the nonlinear properties of azol2 and methyl orange, azol2-MO possesses the advantages of its two constituents and shows larger nonlinear optical properties.     

Third-order nonlinear optical properties of GeSe2-Ga2Se3-PbI2 glasses

The third-order nonlinear optical (NLO) properties of new selenium-based GeSe₂-Ga₂Se₃-PbI₂ glasses have been measured using the optical Kerr effect (OKE) technique, with picosecond and femtosecond laser pulses. The 0.70GeSe₂-0.15Ga₂Se₃-0.15PbI₂ glass has the largest third-order optical nonlinear susceptibility in GeSe₂-Ga₂Se₃-PbI₂ glass system with χ⁽³⁾ of 5.28×10¹² esu. In addition, the response time of glasses is sub-picosecond, which is predominantly associated with electron cloud. Local structure of the glasses has been identified by using Raman studies, while the origins of the observed nonlinear optical response are discussed. The [Ge(Ga)Se₄] tetrahedral and lone-pair electrons from highly polarizable Pb atom in glasses play an important role in enhanced NLO response. These results as well as their good chemical stability indicate that GeSe₂-Ga₂Se₃-PbI₂ glasses are promising materials for photonic applications of third-order nonlinear optical signal processing.     

Chirped optical pulse propagation in saturating nonlinear media

Using a variational method, we have investigated the propagation characteristics of a chirped optical pulse in anomalously dispersive media possessing saturating nonlinearity. For the special case of uniform loss less media, the dynamics of the temporal width of the pulse is shown to be equivalent to an oscillator of unit mass which is executing its motion under some effective potential well. The potential is examined and four different types of behavior of the pulse width are noticed. The role of saturation parameter and the initial chirp in determining the propagation characteristics have been examined. It is found that, both high value of chirp and saturation are detrimental to stable pulse propagation. Particularly, the effect of chirp becomes severe with the increase in the value of saturation. We have shown that incorporation of saturation in the nonlinearity leads to the existence of bistable soliton. For the case of a lossy medium, net broadening of width takes place over many cycles of oscillation. The net broadening decreases with the increase in the value of saturation.     

Linear and nonlinear optical properties of ZnO nanorod arrays

Polarization-dependent linear absorption, second-harmonic generation （SHG） and 3rd-order nonlinearities of wellaligned ZnO nanorod arrays have been investigated with ps pulses. The depressed spectral width and the enhanced intensity of reflective SHG along the long axis of ZnO nanorods were observed by using p-polarized pulses, which is explained by the optical confinements. The nonlinear absorption coefficient measured with s-polarization reached the maximum 4.0×10^4cm/GW at the wavelength -750nm, which revealed a large two-photon resonance absorption attributed to the quantum confined exciton when the polarization is vertical to the long axis of ZnO nanorod.     

Preparation,magnetic and electromagnetic properties of organic magnetic prepolymer containing copper phthalocyanine ring

A novel kind of organic magnetic prepolymer containing copper phthalocyanine ring was prepared via the polymerization of ferrocenyl organic metal magnetic resin (FOMR) with cuprous chloride. The process of prepolymerization was monitored by Fourier transform infrared spectroscopy and ultraviolet–visible spectrophotometry. Magnetic behavior of the samples was studied by a vibrating sample magnetometer.