Second-order nonlinear optical properties of poled coumaromethacrylate copolymers

Second-order nonlinear optical properties of newly designed and synthesized coumaromethacrylate side-chain polymers are reported. The optimum poling conditions were determined experimentally. The optimum poling temperature for these side-chain polymers is well above the glass transition temperature. The second harmonic coefficient of films poled by coronaonset at elevated temperature and the linear electro-optic coefficient of films poled by contact electrodes were measured. The stabilized value of the second harmonic coefficient, d ₃₃, at 1064nm fundamental wavelength was found to be 13 pm/V. The linear electro-optic coefficient, r ₃₃, exhibits strong dispersion ranging from 2 to 12pm/V in the wavelength range 477 to 1115 nm.     

Second-order optical nonlinearity in thermally poled Pyrex borosilicate glass

The thermal poling method was utilized to create second-order optical nonlinearity in Pyrex borosilicate glass. The distribution and amplitude of the induced nonlinearity were characterized with second harmonic microscopy. The induced optical nonlinearity was found in a thin layer around 1.9 μm under the anode surface with a magnitude as high as 0.24 pm/V, comparable to that observed in fused silica samples. SEM observation of the cross-section of the poled glass region, after it had been etched in diluted hydrofluoric acid for several minutes, revealed an etched trench, ∼1.8 μm under the anode edge and ∼0.3 μm in width; while in post-annealed samples, no such etched trench could be observed. The effect of poling voltage on the magnitude of the induced nonlinearity was also studied, where the results showed that higher poling voltage resulted in higher nonlinearity with a threshold of ∼0.9 kV.     

Coupled multiwave interactions in aperiodically poled nonlinear optical crystals

A new type of coupled nonlinear optical interactions that can be implemented in crystals with an aperiodic modulation of the nonlinear susceptibility is studied. The quasi-phase matching condition is satisfied simultaneously for several conventional three-frequency processes involved in the interaction due to the aperiodic variation of the nonlinearity in space. A simple method for designing aperiodically poled nonlinear optical crystals is proposed and analyzed. The method is based on the superposition of nonlinearity modulations produced by several periodic functions simultaneously so that each of these functions individually corresponds to its own quasi-phase-matched nonlinear process. The dynamics of energy exchange during interaction of five waves with different frequencies that involves three coupled three-frequency parametric interaction processes is investigated thoroughly. The ratio between the effective nonlinear wave coupling coefficients and the amplitudes of pump waves is determined for the case in which the initial stage of the interaction is characterized by the parametric instability. It is demonstrated that the secondary simplification of the coupled differential equations with spatially modulated nonlinear coefficients, which leads to the system of equations with constant nonlinear coefficients, correctly describes the dynamics of interaction of the waves at distances of the order of 50 characteristic nonlinear lengths.     

Second-order optical nonlinearity of 10-mum-thick periodically poled LiNbO(3) films

We report on the fabrication and chic((2)) measurements of thin ~10-mum -thick films of periodically poled LiNbO(3), obtained by crystal ion slicing. The d(33) optical coefficient in the films is probed by sum-frequency generation with a short-pulse laser source at 1550 nm and compared with that of the bulk. Efficient, room-temperature TM(omega, m = 0)-to-TM(omega +omega, m = 0) mode conversion is obtained in the films. These measurements show that domain periodicity is preserved during ion implantation and that the thin films have bulklike nonlinearity and material dispersion.     

Second-harmonic generation in poled films of nonlinear optical polymer composites

The second-harmonic generation (SHG) has been measured for studying the molecular ordering and its relaxation process in poled states of two different nonlinear optical (NLO) polymer composites.p-Nitroaniline (pNA) and the azo dye Disperse Orange 3 (DO3) are uniformly dispersed in photopolymer matrices followed by poling. Two different composites made-up of 1 wt% of pNA and 2.5 wt% of DO3 are poled at 200 MV m^-1 and 80 MV m^-1, respectively. One of the second-order NLO coefficients,d ₃₃, was found to be 0.27 pm V^-1 for the pNA-doped film and 0.20 pm V^-1 for the DO3-doped film. While for the latter the ratiod ₃₃/d ₃₃ (3.1) is consistent with the value of 3 in the low-field approximation, for the former the value of 3.5 indicates that higher-order effects of the poling field play a significant role in the NLO process. It is suggested that the SHG relaxation dynamics is also closely related to the UV absorption of the NLO molecules in a photopolymer matrix.     

Second-order nonlinear optical susceptibility in chalcone-group crystalline molecular compounds

A study is reported of the second-order nonlinear optical susceptibility in polycrystalline molecular materials of the chalcone group made by second-harmonic generation at a wavelength of 1.06 μm. Some of the compounds studied exhibit a high nonlinear activity and are transparent in the blue region of the spectrum. The measured macroscopic nonlinear polarizability χ ² was compared with the calculated values of β, the second-order molecular polarizability tensor. The high nonlinear optical polarizability observed in some chalcone compounds is shown to be related to crystal symmetry type. Fiz. Tverd. Tela (St. Petersburg) 41, 2084–2087 (November 1999)     

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 1.06 μm reaches 62 pm/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).     

Efficient femtosecond optical parametric oscillators based on aperiodically poled nonlinear crystals

We discuss the use of aperiodically poled nonlinear crystals to improve conversion efficiency in a synchronously pumped ultrafast optical parametric oscillator. We show theoretically that with these crystals the conversion efficiency can be considerably higher than that obtained when a periodically poled crystal with the same length is used. Moreover, we show that pump threshold can be simultaneously improved by use of longer crystals.     

Spectral and nonlinear optical properties of metal complexes with 1,2-naphthalocyanine in silicate gel matrices

We have studied the influence of the method for embedding metal (Yb or Zn) complexes with 1,2-naphthalocyanine into nanoporous silicate xerogels (directly during sol-gel synthesis or by impregnation of the xerogel) and the nature of the Yb³⁺ exoligand (anionic Cl⁻ or acetylacetone) on the spectral properties and structure of impurity molecular centers. It is shown that the degree of protonation and/or aggregation of the studied metal complexes is determined by the average surface concentration of HO-Si≡ silanol groups of the gel-matrix nanopores. It is established that the Yb complex with 1,2-naphthalocyanine and the anionic ligand Cl⁻ penetrates to the greatest extent from solution into the inner cavities of the xerogel (degree of impregnation). This is due to quasichemical interaction of pigment molecules with the dehydroxylated nanopore surface containing ≡Si-O-Si≡ siloxane bridges. It is shown that the investigated metal complexes in both liquid solutions and solid-state silicate gel-matrices have a limiting effect on powerful optical radiation. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 439–446, July–August, 2007.     

Surface second-harmonic generation based on periodically poled LiNb03 nonlinear optical crystal

We have generated a second-harmonic generation （SHG） of a Q-switched microchip Nd：YAG laser on the surface of a periodically poled LiNbO3 （PPLN） nonlinear crystal near the grazing incidence angle. Three individual SHC waves as transmitted homogeneous, kthomogeneous and reflected radiations have been generated and their intensities are measured and characterized within a desirable range of about 10 different incidence angles of the Nd：YAG laser as pump source on the PPLN surface. The basic of surface nonlinear radiation is also investigated and similar results are calculated and extracted from the theory. Comparison between calculated and measured data shows that they are in good agreement with each other.     

Visualization of the nonlinear optical space-charge region of bulk thermally poled fused-silica glass

We etched thermally poled fused-silica coverslips in 49% HF for 30 s transverse to the poling direction to reveal structural details of the nonlinear region. A peaked ridge below the anode surface, corresponding to a slower etch rate than that of the bulk SiO(2) , was located approximately 5 microm below the anode surface for a poling time of 30 s. The ridge moved deeper into the glass logarithmically with poling time. This trend is qualitatively consistent with a recent model for the formation of the space-charge region that includes injection of hydrogen ions at the anode surface.     

Surface second-harmonic generation based on periodically poled LiNbO3 nonlinear optical crystal

We have generated a second-harmonic generation(SHG) of a Q-switched microchip Nd:YAG laser on the surface of a periodically poled LiNbO3(PPLN) nonlinear crystal near the grazing incidence angle.Three individual SHG waves as transmitted homogeneous,inhomogeneous and reflected radiations have been generated and their intensities are measured and characterized within a desirable range of about 10 different incidence angles of the Nd:YAG laser as pump source on the PPLN surface.The basic of surface nonlinear radiation is also investigated and similar results are calculated and extracted from the theory.Comparison between calculated and measured data shows that they are in good agreement with each other.     

Characterization of a second-order nonlinear layer profile in thermally poled optical fibers with second-harmonic microscopy

Second-harmonic microscopy has been successfully applied to characterize the second-order nonlinear layer in optical fibers thermally poled at 280 degrees C and 3.5 kV for 30 min. The nonlinear layer was found to be approximately 5.1 microm deep under the anode and was not always centered about the closest point between the electrodes.     

Second-order nucleon-nucleus optical potential

The second-order nucleon-nucleus optical potential has been calculated by using a simple second-order perturbation formalism. The results obtained by using an effective energy denominator indicate that the closure approximation is not valid for scattering.     

Second-order nonlinear susceptibilities of surfaces

Systematic studies were carried out with the goal to further develop optical Second-Harmonic Generation (SHG) as a tool for surface and interface analysis. For this purpose hexadecane thiol, HS(CH₂)₁₅CH₃, on polycrystalline Au films served as a model system to study the spectral behavior of the susceptibility of the gold surface and its variation as a function of coverage. Experiments have been performed at different coverages, with different polarization combinations of the incident and detected light, different angles of incidence and different wavelengths ranging from z=615 nm to 660 nm. In addition to the intensity of the generated second-harmonic light, its phase was measured. As a result, a complete determination of all independent elements of the susceptibility tensor became possible. The studies with different excitation wavelengths reveal the presence of resonances of the tensor elements and strikingly demonstrate the importance of phase measurements for an unambiguous interpretation of the data. The superposition of resonant contributions originating from different elements of the susceptibility tensor is discussed and gives rise to very distinct and peculiar spectral features.Paper presented at the 129th WE-Heraeus-Seminar on Surface Studies by Nonlinear Laser Spectroscopies, Kassel, Germany, May 30 to June 1, 1994     

足球烯分子三阶非线性光学性质的研究

报道了有关足球烯分子甲苯溶液中简并四波混频实验.测量出足球烯C_(70)分子和C_(60)分子的三阶超极化率张量y_(1111)分量分别为1.2×10~(-30)esu和4.0×10~(-31)esu.对应于固体样品的三阶非线性光学系数X_(1111)分量分别是2.5×10~(-8)esu和8.5×10~(-9)esu.此结果表明了足球烯分子是现有的非线性光学材料中具有较大三阶非共振电子极化率材料之一.文中还利用自由电子模型解释了非线性光学极化率的起源.     

Ultrafast optical nonlinear properties of metal nanoparticles

The physical origin and the dynamics of the ultrafast optical nonlinear response of noble metal nanoparticles are analyzed around the surface plasmon resonance frequency using extension of the bulk metal electron kinetics and band structure models. The computed spectral and temporal responses are found to be in very good agreement with the measured ones in silver when taking into account the impact of electron excitation on both the interband absorption and electron optical scattering rate. A good reproduction of the strong excitation regime experimental results is also obtained in the case of gold, with a dominant contribution of the interband effect. Received: 4 July 2001 / Published online: 10 October 2001     

CuO薄膜的三阶非线性光学特性研究

采用脉冲激光沉积技术在Si(100)和熔石英基片上制备了单相的CuO薄膜.通过X射线衍射仪,拉曼光谱仪,场发射扫描电镜和紫外可见光光度计对薄膜的结构,表面形貌和光学性质进行了表征. 场发射扫描电镜结果表明CuO薄膜中晶粒排列致密且分布均匀,其尺寸约为45nm.结合飞秒激光(800nm,50fs)和Z扫描方法测量了薄膜的三阶非线性光学特性,结果表明CuO薄膜具有超快的非线性光学响应且非线性折射率和非线性吸收系数均为负值,其大小分别为-3.96×10^-17 m^{2< 关键词： CuO薄膜 Z-扫描')" href="#">Z-扫描 三阶光学非线性}     

掺杂石墨烯系统电场调控的非线性太赫兹光学特性研究

石墨烯是单原子厚的二维狄拉克相对论费米子系统,其优秀的光电学性质得到了广泛的关注和研究. 本论文利用量子理论研究掺杂石墨烯系统外电场和光场共同作用下的非平衡载流子的非线性太赫兹光学性质. 研究发现,掺杂石墨烯带内光吸收表现出强的非线性太赫兹光学特性. 随着外加偏压电场的增大,石墨烯非线性光学响应增强;随着外界太赫兹光频率的减小,非线特性增强. 研究表明通过改变电场强度,可以有效调节石墨烯系统太赫兹非线性光学特性. 研究结果为探索和发展以石墨烯为基础的新型纳米太赫兹光电器件的研究和实际应用提供了理论依据. 关键词： 石墨烯 太赫兹 非线性 光电流     

Elastic,optical and nonlinear optical properties of InPS4

Indium phosphorus sulfide, a promising nonlinear optical material, is investigated with respect to elastic constants, anisotropic sound velocity, absorption, refraction and nonlinear optical applications. The elastic tensor components are evaluated from phonon frequency and wavevector data obtained by Brillouin scattering. The ordinary and extraordinary dispersion is determined for the entire transparency range (0.4–8 μm). A 5-parameter Sellmeier equation is fitted to these data and is used to calculate phase matching diagrams for second-harmonic generation and general three-frequency mixing. A possible, attractive application, angle tuned parametric oscillation, is discussed.