Synthesis and Crystal Growth of Stilbazolium Derivatives for Second‐Order Nonlinear Optics

A series of ionic stilbazolium salts with benzenesulfonates with different substituents in the para position have been synthesized. Single crystals of 4‐N,N‐dimethylamino‐4′‐N′‐methylstilbazolium p‐methoxybenzenesulfonate (DSMOS) were successfully grown in methanol solution by slow cooling. X‐ray studies revealed that DSMOS crystallized in the triclinic space group P1 with its molecular dipoles perfectly aligned in one direction—favorable for large nonlinear optical and electro‐optical effects. Kurtz powder tests revealed a large powder second‐harmonic generation efficiency that is similar to that of the well‐studied 4‐N,N‐dimethylamino‐4′‐N′‐methylstilbazolium tosylate (DAST).     

Poled Sol–Gel Materials With Heterocycle Push–Pull Chromophores that Confer Enhanced Second‐Order Optical Nonlinearity

Hybrid organic–inorganic materials doped with zwitterionic push–pull chromophores with high hyperpolarizability have been synthesized by a sol–gel procedure. A large chromophore concentration was reached by using N‐(hydroxyethyl)carbazole as a physical spacer (preventing the dye aggregation). Spin‐coated doped films were electrically poled and second harmonic generation measurements performed in situ. During the thermally assisted poling under a N₂ atmosphere, only the carbazole molecules degraded. Second‐harmonic generation measurements gave an estimation of the nonlinear coefficient, r₃₃, of 38 pm V^–1 at 1064 nm.     

Layer‐Structured Photoconducting Polymers: A New Class of Photorefractive Materials

We study the photorefractive (PR) properties of a new kind of low glass‐transition temperature (T_g) polymer composite based on layered photoconductive polymers, poly(p‐phenylene terephthalate) carbazoles (PPT‐CZs). These photoconductors consist of the rigid backbone of PPT with pendant oxyalkyl CZ groups. The compounds are doped with the photosensitizer C₆₀ and nonlinear optical chromophores diethylaminodicyanostyrene (DDCST), and no plasticizers are added. When the host polymers are mixed with various PR ingredients, the layers are preserved and their layer distance increases, indicating that all the guest molecules are confined to the nanoscale interlayer space. These composites showed very low T_g values (< ? °C). Despite the absence of a plasticizer and the lower concentration of the carbazole photoconductive moieties as compared to poly(N‐vinylcarbazole) systems, these materials show excellent PR properties, i.e., a PR gain of Γ = 250 cm^–1 under an external electric field of 60 V μm^–1, and diffraction efficiency and PR sensitivity of 93 % and 24 ± 7 cm² kJ^–1 at E = 100 V μm^–1, respectively.     

激光防护材料的研究现状及发展趋势

根据激光辐射对眼睛的损伤规律,分析了激光对人眼和装备传感器的损伤,简述了激光的应用与防护,介绍了激光防护材料的技术指标、类型、性能以及国外对激光防护材料的应用,重点分析并指出了今后激光防护材料的发展方向。     

Organic Phenolic Configurationally Locked Polyene Single Crystals for Electro‐optic and Terahertz Wave Applications

We investigate a configurationally locked polyene (CLP) crystal 2‐(3‐(4‐hydroxystyryl)‐5,5‐dimethylcyclohex‐2‐enylidene)malononitrile (OH1) containing a phenolic electron donor, which also acts as a hydrogen bond donor. The OH1 crystals with orthorhombic space group Pna2₁ (point group mm2) exhibit large second‐order nonlinear optical figures of merit, high thermal stability and very favorable crystal growth characteristics. Higher solubility in methanol and a larger temperature difference between the melting temperature and the decomposition temperature of OH1 compared to analogous CLP crystals, are of advantage for solution and melt crystal growth, respectively. Acentric bulk OH1 crystals of large sizes with side lengths of up to 1 cm with excellent optical quality have been successfully grown from methanol solution. The microscopic and macroscopic nonlinearities of the OH1 crystals are investigated theoretically and experimentally. The OH1 crystals exhibit a large macroscopic nonlinearity with four times larger powder second harmonic generation efficiency than that of analogous CLP crystals containing dimethylamino electron donor. A very high potential of OH1 crystals for broadband THz wave emitters in the full frequency range of 0.1–3 THz by optical rectification of 160 fs pulses has been demonstrated.     

Photorefractive Performance of Hyperstructured Cyclotriphosphazene Molecular Glasses containing Carbazole Moieties

Two hyperstructured photorefractive (PR) molecular glasses ( M1 and M2 ) with a cyclotriphosphazene core are synthesized via nucleophilic substitution and an azo‐coupling reaction. These molecules exhibit excellent solubility in common organic solvents and maintain a complete amorphous state in spite of their high glass‐transition temperature. The nonlinear optical effects, two‐beam coupling and four‐wave mixing, respectively, are used to prove the PR performance in the optically transparent films of M1 and M2 doped with 30 % N‐ethyl‐carbazole. With no external electric field, a gain coefficient of 102 cm^–1 and diffraction efficiency of 24 % are obtained in the composite made from M1 , and an even higher gain coefficient of 214 cm^–1 and diffraction efficiency of 31 % are obtained in the composite made from M2 owing to its higher chromophore loading.     

Electro‐optical Materials: Switching of Electrically Responsive,Light‐Sensitive Colloidal Suspensions of Anisotropic Pigment Particles (Adv. Funct. Mater. 3/2011)

An unusual electro‐optical behavior of colloidal suspensions of dichroic, elongated (rod‐shaped) pigment particles is reported. These suspensions exhibit nematic liquid crystal order at low volume fraction of the suspended particles (<15 wt%) and show a strong electric and optical response to an external electric field. Additionally, the characteristics of the optical response can be reversibly manipulated by illuminating the sample with light in its absorption band. The suspensions show a number of interesting phenomena like homeotropic‐planar orientational transitions and light‐induced pattern formation.     

LiInS2: A new nonlinear crystal for the mid-IR

Second harmonic generation for fundamental wavelengths between 2.3 and 6 μm and optical parametric generation from 5 to 12 μm in the mid-IR are demonstrated in a new nonlinear crystal, LiInS₂, exhibiting no two-photon absorption near 800 nm. Photoinduced absorption in the visible to near-IR occurring at λ<450 nm excitation can be removed with illumination at λ>500 nm or minimized by annealing in In₂S₃ vapor.     

Co~(2+)∶LiNbO_3晶体的坩埚下降法生长及其光谱性质

应用坩埚下降法,以同成分化学摩尔分数比(Li2O:48.6%,Nb2O5:51.4%)为原料,以CoO作为掺杂物,在合适的温度梯度(20~40℃/cm)与生长速度(1~3mm/h),生长出了Co2+掺杂摩尔分数分别为0.1%与0.3%的LiNbO3(LN)晶体。用X射线衍射(XRD)与差热分析(DTA)表征了获得的晶体。测定了不同部位晶体从350~2500nm的吸收光谱。观测到520nm,549nm与612nm三个分裂的尖吸收峰以及以1358nm为发光中心的吸收带。从吸收特性表明,Co离子掺杂于畸变的氧八面体中,呈现+2价态,并且沿着晶体生长方向浓度逐渐减少,Co2+在LiNbO3晶体中的有效分凝系数大于1。研究了不同部位晶体在900nm以下的荧光光谱特性,在750nm发现有较强的荧光发射,并随着激发波长的增长,荧光发生红移。     

Dragonfly‐Eye‐Inspired Artificial Compound Eyes with Sophisticated Imaging

The natural compound eye is a striking imaging device with a wealth of fascinating optical features such as a wide field of view (FOV), low aberration, and high sensitivity. Dragonflies in particular possess large, sophisticated compound eyes that exhibit high resolving power and information‐processing capacity. Here, a large‐scale artificial compound eye inspired by the unique designs of natural counterparts is presented. The artificial compound eye is created by a high‐efficiency strategy that combines single‐pulse femtosecond laser wet etching with thermal embossing. These eyes have a macrobase diameter of 5 mm and ≈30 000 close‐packed ommatidia with an average diameter of 24.5 μm. Moreover, the optical properties of the artificial compound eyes are investigated; the results confirm that the eye demonstrates advanced imaging quality, an exceptionally wide FOV of up to 140°, and low aberration.     

Quadratic Optical Nonlinearities of N‐Methyl and N‐Aryl Pyridinium Salts

Four series of dyes with dimethylamino electron donor groups and N‐R‐pyridinium (R = methyl Me, phenyl Ph, 2,4‐dinitrophenyl 2,4‐DNPh, or 2‐pyrimidyl 2‐Pym) electron acceptors are studied as their hexafluorophosphate salts. The intramolecular charge‐transfer (ICT) energies (E_max) of these compounds decrease within each of the series in the order R = Me > Ph > 2,4‐DNPh > 2‐Pym, as the electron‐accepting ability of the pyridinium ring increases. Hyper‐Rayleigh scattering with femtosecond 1300 or 800 nm lasers yields fluorescence‐free first hyperpolarizabilities β, and static first hyperpolarizabilities β₀[H] are obtained via the two‐state model. Dipole moment changes Δμ₁₂ for the ICT transitions obtained from Stark spectroscopy afford β₀[S] values by using β₀ = 3Δμ₁₂(μ₁₂)²/2(E_max)² (μ₁₂ = transition dipole moment). The β₀[S] data show that the combination of pyridyl N‐arylation with conjugation extension affords large increases in β₀. The β₀[H] data generally agree with this conclusion, but resonance effects may explain some apparent anomalies. X‐ray structural studies on various salts reveal that the use of tosylate anions is not a generally applicable approach to engineering noncentrosymmetric structures of pyridinium salts. However, trans‐N‐phenyl‐4‐(4‐dimethylaminophenyl‐4‐buta‐1,3‐dienyl)pyridinium hexafluorophosphate adopts the polar space group Cc, and shows a very large powder second harmonic generation efficiency from a 1907 nm laser, which is similar to that of the well‐studied material trans‐4′‐(dimethylamino)‐N‐methyl‐4‐stilbazolium tosylate (DAST).