中心对称萘酞菁分子二次谐波产生的实验研究

研究了三种萘酞菁化合物LB膜的制备,并通过二次谐波产生的方法研究了单个对称取代的萘酞菁化合物及双(四叔丁基萘酞菁)铒的二阶非线性光学特性,并对它们的产生机理进行了简单的讨论.单个对称取代的萘酞菁化合物,它们的二次谐波产生机制为磁偶极子耦合机制,双(四叔丁基萘酞菁)铒的二阶非线性光学特性起源于电四极子模型,且它的二阶非线性极化率χ(2)(或超极化率β)大于单个萘酞菁化合物.     

半导体材料AAl2C4(A=Zn, Cd, Hg; C=S, Se)的电子结构和光学性质

采用基于密度泛函理论的第一性原理方法, 对具有缺陷型黄铜矿结构的半导体材料A^ⅡAl₂C₄^Ⅵ(A=Zn, Cd, Hg; C =S, Se)的构型和电子结构进行研究, 并系统考察了各晶体的光学性质. 对于线性光学性质, 五种晶体在红外区和部分可见光区具有良好的透光性能, 其中HgAl₂S₄和HgAl₂Se₄晶体具有适中的双折射率. 在非线性光学性质方面, 该类晶体倍频效应较强, 理论预测得到的二阶静态倍频系数均较大(>20 pm/V). 体系的倍频效应主要来源于价带顶附近以S/Se 价p轨道为主要成分的能带向含有较多Al/Hg 价p成分的空带之间的跃迁. 通过与已商业化的AgGaC₂晶体光学性质的对比, 结果表明HgAl₂S₄和HgAl₂Se₄是一类性能优良的红外非线性光学晶体材料.     

Study of structural phase transitions by techniques of nonlinear optics

The paper is intended to illustrate that nonlinear optical phenomena yield useful information about structural phase transitions in crystals. Emphasis is placed on collinear second harmonic generation (SHG) and on second harmonic scattering (SHS). The temperature dependence of higher-rank tensors describing SHG is discussed in detail and is related to variations of long- and short-range order. Several kinds of SHS are considered and explained by modulations of the nonlinear optical susceptibility. Particular attention is paid to results obtainable by SHS, but not by ordinary scattering of light.     

半花菁／氮冠（醚）交替LB多层膜的二阶光学非线性性质

对一种新型的，具有双脂链的盘状非活性分子氮冠（醚）（ＮＣ）ＬＢ膜进行了表征。小角Ｘ射线衍射（ＳＡＸＤ）结果表明：纯ＮＣ分子可以形成非常好的ＬＢ膜有序结构。将它与活性分子半花菁（ＤＡＥＰ）制备成Ｙ型交替多层膜，由于半花菁分子的单脂链（长尾）可以镶嵌在ＮＣ分子的双脂链之间，改善了多层膜的结构有序性及稳定性，从而得到二次谐波强度随层数的变化在１￣１１６双层范围内显示出较理想的平方关系。通过二次谐波的测量     

ZnO–TeO2–Yb/Tm glasses with silver nanoparticles as laser operated quantum electronic devices

The incorporation of silver nanoparticles into a Yb/Tm codoped ZnO–TeO₂ glass is shown to lead to a substantial increase in optically stimulated second harmonic generation (SHG). The corresponding second order optical susceptibility is equal to 1.32 pm/V at a wavelength of 1064 nm. The optimal conditions required the thermoannealing of the sample for 48 h and the use of a pump-probe delaying time of 12 ns.     

Second- and third-harmonic generations for a nondilute suspension of coated particles with radial dielectric anisotropy

We derive expressions for the effective nonlinear susceptibility tensors for both the second harmonic generation (SHG) and induced third harmonic generation (THG) of nonlinear composite materials, in which nondilute coated particles with radial dielectric anisotropy are randomly embedded in the linear host. Two types of coated particles are considered. The first is that the core possesses a second order nonlinear susceptibility and the shell is linear and radially anisotropic, while the second is that the core is linear with radial anisotropy and the shell has a second order nonlinear susceptibility. We observe greatly enhanced SHG and THG susceptibilities at several surface plasmon resonant frequencies. For the second model, due to the coating material being metallic, there exists two fundamental resonant frequencies ω_c1 and ω_c2, whose difference ω_c2-ω_c1 is strongly dependent on the interfacial parameter and the radial dielectric anisotropy. Furthermore, in both systems, the adjustment of the dielectric anisotropy results in larger enhancement of both SHG and induced THG susceptibilities at surface plasmon resonant frequencies than the corresponding isotropic systems. Therefore, both the core-shell structure and the dielectric anisotropy play important roles in determining the nonlinear enhancement and the surface resonant frequencies.     

Enhancement of the second harmonic generation from monolayer WS2 coupled with a silica microsphere

Monolayer transition metal dichalcogenides (TMDs) are widely used for integrated optical and photoelectric devices. Owing to their broken inversion symmetry, monolayer TMDs have a large second-order optical nonlinearity. However, the optical second-order nonlinear conversion efficiency of monolayer TMDs is still limited by the interaction length. In this work, we theoretically study the second harmonic generation (SHG) from monolayer tungsten sulfide (WS₂) enhanced by a silica microsphere cavity. By tuning the position, size, and crystal orientation of the material, second-order nonlinear coupling can occur between the fundamental pump mode and different second harmonic cavity modes, and we obtain an optimal SHG conversion efficiency with orders of magnitude enhancement. Our work demonstrates that the microsphere cavity can significantly enhance SHG from monolayer 2D materials under flexible conditions.     

4-硝基-4′-氨基偶氮苯的光学性质研究

采用紫外可见吸收和二次谐波产生技术研究了“推-拉”型偶氮苯分子Langmuir-Blodgett(LB)膜的光谱和二阶非线性光学特性.4-硝基-4′-氨基偶氮苯(NAA)分子能制成很好的LB多层膜,在稀溶液中以单体的反式异构体形式存在,在膜中主要以J-聚集体的形式存在,LB膜的紫外可见吸收谱的吸收峰较之溶液的发生了52 nm的红移.NAALB膜的二阶非线性极化率χ(2)为19.59×10－8 esu,一阶超极化率β值较大,约为1.974×10－29 esu.其光学二阶非线性起源于电偶极子机制.     

ZnS/PVA nanocomposites for nonlinear optical applications

We have found a correlation between ZnS nanocomposite nonlinear optical features and technological processing using electrolytic method. In the earlier researches this factor was neglected. However, it may open a new stage for operation by photovoltaic features of the well known semiconductors within a wide range of magnitudes. The titled nanostructured zinc sulfide (ZnS) was synthesized by electrolytic method. The obtained ZnS nano-crystallites possessed nano-particles sizes varying within 1.6 nm…1.8 nm. The titled samples were analyzed by XRD, HR-TEM, STEM, and nonlinear optical methods such as photo-induced two-photon absorption (TPA) and second harmonic generation (SHG). For this reason the nano-powders were embedded into the photopolymer poly(vinyl) alcohol (PVA) matrices. Role of aggregation in the mentioned properties is discussed. Possible origin of the such correlations are discussed.     

UV-induced two-photon absorption in BiB3O6 single crystals

We show that BiB₃O₆ (BiBO) crystals, well known for their excellent second harmonic generation (SHG) properties, may also be of interest for third-order optical phenomena, particularly for two-photon absorption (TPA). Photoinduced TPA measurements were performed under illumination of excimer Xe–F laser (λ = 217 nm) as a photoinducing (pumping) beam. It created a thin surface layer (about 85 nm) that was a source of the observed photoinduced TPA. Raman shifted Nd-YAG laser radiation (λ = 1.9 μm) as well as its second and fourth harmonics (λ = 950 and λ = 475 nm, respectively) were used as fundamental (probing) beams of the TPA. The highest values of the TPA β coefficient were achieved for a polarization of the pumping light directed along crystallographic axis b. Quantum chemical simulations indicate on substantial contribution of UV-induced electron–phonon anharmonicity to the observed TPA. The obtained values of TPA coefficients indicate a possibility of using BiBO crystals as UV-operated optical limiters in a wide spectral range.     

A generalized Ginzburg-Landau approach to second harmonic generation

We develop a generalized Ginzburg-Landau theory for second harmonic generation (SHG) in magnets by expanding the free energy in terms of the order parameter in the magnetic phase and the susceptibility tensor in the corresponding high-temperature phase. The non-zero components of the SHG susceptibility in the ordered phase are derived from the symmetries of the susceptibility tensor in the high-temperature phase and the symmetry of the order parameter. In this derivation, the dependence of the SHG susceptibility on the order parameter follows naturally, and therefore its nonreciprocal optical properties. We examine this phenomenology for the magnetoelectric compound Cr₂O₃ as well as for the ferroelectromagnet YMnO₃. Received 27 August 1999     

Voigt位型下电介质/反铁磁/电介质结构二次谐波生成非倒易性研究

利用非线性传递矩阵方法研究了Voigt位型下电介质/反铁磁/电介质 结构二次谐波生成的非倒易性. 研究发现外加静磁场反向和电介质层排序翻转均对二次谐波输出产生影响, 出现了二次谐波生成的非倒易性. 二次谐波生成非倒易性频率区域在反铁磁共振区, 此区间正处于THz频段. 随着入射角度的增加, 非倒易性的效果越来越明显. 研究二次谐波生成的非倒易性, 可为反铁磁器件的设计加工提供理论支持.     

Size effect on the SHG properties of Cu-doped CdI2 nanocrystals

Because the optically induced second harmonic generation (SHG) is prevented by symmetry in a centrosymmetric material, one needs to form noncentrosymmetric processes in order to observe the SHG. However, one of the efficient ways to enhance the noncentrosymmetricity of a material is to dope it with an appropriate impurity and amount. We grow Cu-doped CdI₂ layered nanocrystal structures from the mixture of CdI₂ and CuI using the standard Bridgman-Stockbarger method and investigate the nano-confined effects by studying the second-order optical effect via the measurements of SHG. The second-order susceptibility for the nanocrystals is calculated and the values at liquid helium temperature range from 0.38 to 0.83 pm V⁻¹ for the thicknesses of 10-0.8 nm respectively. The size dependence demonstrates the nano-sized quantum-confined effect with a clear increase in the SHG with decreasing the thickness of the nanocrystal or crystal temperature. Since the local electron-phonon anharmonicity is described by third-order rank tensors in disordered systems, the SHG is very similar to that one introduced for the third-order optical susceptibility. It has been confirmed by observing the large photoluminescent yield of the pure crystals. The Raman scattering spectra taken for thin nanocrystals confirm the phonon modes originating from interlayer phonons crucially responsible for the observed effects. The obtained results show that the Cu-doped CdI₂ layered nanocrystals are promising materials for applications in optoelectronic nano-devices.     

稳定高质量光参量啁啾脉冲放大系统优化设计

要实现光参量啁啾脉冲放大(OPCPA)系统稳定、高质量输出,需要同时对光参量放大和泵浦光倍频这两个非线性过程进行优化设计。在光参量放大系统优化设计中,建立了描述光参量放大过程的多种简化物理模型;通过模拟泵浦光和信号光口径匹配关系,分析了放大信号光空间两维对称性并提出了优化方法;建立了非线性晶体最佳长度确定及调谐方法,以实现信号光输出高稳定性。在泵浦光倍频系统优化设计过程中,提出应用位相失配法实现稳定倍频输出,研究表明这种方法不仅能实现倍频光能量起伏抖动远远小于基频光能量的起伏抖动,而且能减小泵浦光近场调制度和时间波形调制,极大地改善输出倍频光光束质量,进而提高OPCPA系统输出信号光质量。     

Second harmonic generation in α-Si:H thin films: Thickness dependence

The second harmonic generation (SHG) technique has been applied to investigate the nonlinear optical properties of thin films of hydrogenated amorphous silicon on a glass substrate. SHG measurements have been performed in two transmission experimental schemes. Modeling of a film as a three-layer structure and considering the interference and absorption at the SH wavelength have been carried out. The dependence of the nonlinear susceptibility on the film thickness was used to separate the bulk electric dipole contribution.     

非对称耦合量子阱Zn1-xCdxSe/ZnSe的二次谐波产生及其光学各向异性研究

采用反射式二次谐波产生方法对非对称Ⅱ-Ⅵ族耦合量子阱Zn1-xCdxSe/ZnSe的非线性光学特性进行了研究。与衬底相比,非对称量子阱在可见光波段的二次谐波信号增强一个量级以上。测量和比较了室温下量子阱样品与衬底样品的荧光光谱,研究了在入射光和反射光均为p偏振,以及入射光和反射光分别为s偏振和p偏振两种情况下,二次谐波强度随样品旋转方位角的变化关系,可见其有非常明显的二阶非线性一光学各向异性。     

Linear and nonlinear optical properties of yttrium formate dihydrate,Y(HCOO)<Subscript>3</Subscript>·2H<Subscript>2</Subscript>O

Yttrium formate dihydrate, Y(HCOO)₃·2H₂O (point group 222), a promising new material for Raman laser frequency converters, has been reinvestigated with respect to the linear and nonlinear optical (second-harmonic generation, SHG) properties. High-precision data of refractive indices and their dispersion in the wavelength range 365–1083 nm are given, together with the three independent components of the tensor of nonlinear optical susceptibility (SHG) [d_ijk ^SHG]. A calculation of the macroscopic nonlinear optical susceptibility from the hyperpolarizabilities of the formate groups results in good agreement with the experimental values. This signals that the nonlinear optical interaction in Y(HCOO)₃·2H₂O can mainly be attributed to the formate groups. PACS 42.65.Ky; 42.70.Mp; 78.20.Ci     

Laser nonlinear-optical probing of silicon/SiO2 interfaces: Surface stress formation and relaxation

A nonlinear optical technique based on optical second harmonic generation in reflection is shown to provide information on the surface layer structure of semiconductor crystals, thin films and layered systems. The second harmonic intensity is sensitive to inhomogeneous stress in centrosymmetric materials via spatial selection rules and the appearance of an electric dipole contribution to the second order nonlinear optical susceptibility. The technique is used to monitor mechanical stress relaxation in the SiO₂/Si interface during several annealing procedures.     

Second harmonic generation in planar optical waveguides

We study optical second harmonic generation (SHG) in planar waveguide structures composed of several layers with different dielectric constants. We develop a general formalism for the calculation of mode generation by a planar antenna embedded in the waveguide. As an application we consider a monolayer of high second-order susceptibility adsorbed at the interface between two layers of the waveguide structure. Periodic modulation of the nonlinear susceptibility allows phase matching leading to dramatically enhanced second harmonic intensities. We investigate the SHG-efficiency of various experimentally realizable geometries.     

Measurement of ultrashort laser pulses using single-crystal films of 4-aminobenzophenone

Single-crystal thin-film of an organic second-order nonlinear optical material, 4-aminobenzophenone (ABP), is used to measure the pulsewidth of a Ti-Sapphire laser producing 45 fs pulses at 1 kHz repetition rate, by the non-collinear second-harmonic generation (SHG) intensity autocorrelation technique. These films are suitable for measurements over a broad wavelength range, down to 780 nm, due to their wide optical transparency. The single-crystal film with thickness (3 μm) less than the coherence length requires no phase-matching for efficient broadband SHG. Pulse walk-off due to group-velocity mismatch (GVM) and temporal broadening of the pulses due to group-velocity dispersion (GVD) are found to be negligible. These effects have been estimated for pulse width down to few-cycle pulses (10 fs), and the analyses show that these films can be used to characterize such ultrashort optical pulses.