Enhancement of optical nonlinearity in a guest-host system by nematic ordering

Second-harmonic generation (SHG) has been studied for understanding the enhancement mechanism for the second-order optical nonlinearity by the nematic (or axial) ordering in a liquid crystal doped with one-dimensional nonlinear optical (NLO) organic molecules. An extended version of the Maier-Saupe mean-field theory for nematic liquid crystals was developed to obtain analytical expressions for the second-order NLO coefficients in terms of the axial order, the polar order and the effective nematic potential. From the SHG data in a guest-host system composed ofN,N'-dimethylaminonitrostilbene molecules (0.5% by weight) and a liquid crystal, the enhancement of the second-order NLO coefficient,d ₃₃, by nematic ordering becomes almost 3, which agrees well with our theoretical predictions.     

聚合物薄膜中生色团分子间的相互作用对其宏观二阶非线性的影响

制备了3-(1,1-二氰基噻吩)-1-苯-4,5-二羟基-H-噻唑(DCNP)与聚醚醚酮(PEK-c)组成的主客掺杂聚合物薄膜,用Maker条纹法测量了不同掺杂浓度下薄膜的二阶非线性系数χ₃₃⁽²⁾.实验结果表明,聚合物中生色团的含量高到一定程度,其宏观二阶非线性随生色团含量的增加反而下降.本文在考虑聚合物中生色团分子相互作用的情况下,修正了聚合物宏观二阶非线性与生色团的含量之间的关系,此时聚合物宏观二阶非线性与生色团的含量已非简单的正比关系.讨论了生色团分子间 关键词：     

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.     

Linear and Nonlinear Optical Properties Of Racemic (±)2-(α-Methylbenzylamino)-5-Nitropyridine Single Crystals

Linear and nonlinear optical properties of racemic (±)2-(α-methylbenzylamino)-5-nitropyridine ((±)MBANP) single crystals have been comprehensively investigated and compared with those of the enantiomorph (–)2-(α-methylbenzylamino)-5-nitropyridine ((–)MBANP) crystals. (±)MBANP crystal exhibits very high chemical and physical stability, but relatively small nonlinear optical coefficients (d₃₁ = 6.8 pm/V, d₃₂ = 4.7 pm/V, d₃₃ = 0.84 pm/V). A comparison between the nonlinear optical coefficients of (±)MBANP and (–)MBANP demonstrates the validity of the oriented-gas model in molecular crystals that neglects all the contributions from intermolecular interaction.     

Investigation of the polyetherketone guest–host DR1/PEK-c polymer films by real-time monitoring of the second-harmonic generation

The real-time monitoring of the second-harmonic generation (SHG) was used to optimize the poling condition and to study the nonlinear optical (NLO) properties of the polyetherketone (PEK-c) guest–host polymer films. The high second-order NLO coefficient χ₃₃⁽²⁾=11.02 pm/v measured at 1.064 μm was achieved when the weight percent of DR1 guest in the polymer system is 20%. The NLO activity of the poled DR1/PEK-c polymer film can maintain more than 80% of its initial value when temperature is under 100°C, and the normalized second-order NLO coefficient can maintain more than 85% after 2400 s at 80°C.     

Study on the second-harmonic-generation of GdCa4O(BO3)3 crystals along various phase-matching directions

In this paper, the theoretical calculations of d_eff of GdCa₄O(BO₃)₃ (GdCOB) along various phase-matching (PM) directions are reported. It is shown that the maximum d_eff is out of the main planes and the d_eff in the range of (0<θ≤90, 90<φ≤180) are larger than that in the range of (0<θ≤90, 0≤φ≤90). The PM direction along (θ=66.8, φ=132.6) for GdCOB crystal has the largest d_eff. Second-harmonic-generation (SHG) experiments were performed on GdCOB crystal along various PM directions. The results show that in GdCOB crystal, the intracavity SHG conversion efficiency is 27.6% along the PM direction (θ=66.8, φ=132.6) which is larger than that along PM directions in XY and XZ main planes, which are in good agreement with the theoretical calculations. The continuous-wave (cw) green laser output power is 1.22 W when LD pump power is 10 W in the Nd:YVO₄/GdCOB laser.     

Properties of Sr- and Sb-doped PZT–Portland cement composites

Lead zirconate titanate (PZT) ceramic-cement-based composites have increasingly been recognized as an attractive new composite material for use as a sensor in structural applications. In this work, PZT was doped with Sr and Sb (PSZT) to give it greater dielectric constant (ε _r) and higher piezoelectric coefficient (d ₃₃) values than normal PZT and is the first time that it is mixed with normal Portland cement to produce a 0–3 connectivity PSZT–Portland cement composite using PSZT contents of 50% and 70% by volume. Scanning electron micrographs show PSZT ceramic particles closely surrounded by the hydrated cement matrix where a dense microstructure can be observed in the interfacial zone. Both the ε _r and d ₃₃ values were found to increase with PSZT content and the values are amongst the highest so far for these types of composites, where the ε _r and d ₃₃ values reached 590 and 48 pC/N, respectively.     

The influence of different doping elements on microstructure, piezoelectric coefficient and resistivity of sputtered ZnO film

ZnO film is attractive for high frequency surface acoustic wave device application when it is coupled with diamond. In order to get good performance and reduce insertion loss of the device, it demands the ZnO film possessing high electrical resistivity and piezoelectric coefficient d₃₃. Doping ZnO film with some elements may be a desirable method. In this paper, the ZnO films undoped and doped with Cu, Ni, Co and Fe, respectively (doping concentration is 2.0 at.%) are prepared by magnetron sputtering. The effect of different dopants on the microstructure, piezoelectric coefficient d₃₃, and electrical resistivity of the film are investigated. The results indicate that Cu dopant can enhance the c-axis orientation and piezoelectric coefficient d₃₃, the Cu and Ni dopant can increase electrical resistivity of the ZnO film up to 10⁹ Ω cm. It is promising to fabricate the ZnO films doped with Cu for SAW device applications.     

Second-order optical susceptibility in doped III-V piezoelectric semiconductors in the presence of a magnetostatic field

A detailed analytical investigation of second-order optical susceptibility has been made in moderately doped III-V weakly piezoelectric semiconductor crystal, viz. n-InSb, in the absence and presence of an external magnetostatic field, using the coupled mode theory. The second-order optical susceptibility arises from the nonlinear interaction of a pump beam with internally generated density and acoustic perturbations. The effect of doping concentration, magnetostatic field and pump intensity on second-order optical susceptibility of III-V semiconductors has been studied in detail. The numerical estimates are made for n-type InSb crystals duly shined by pulsed 10.6 μm CO₂ laser and efforts are made towards optimising the doping level, applied magnetostatic field and pump intensity to achieve a large value of second-order optical susceptibility and change of its sign. The enhancement in magnitude and change of sign of second-order optical susceptibility, in weakly piezoelectric III-V semiconductor under proper selection of doping concentration and externally applied magnetostatic field, confirms the chosen nonlinear medium as a potential candidate material for the fabrication of nonlinear optical devices. In particular, at B ₀ = 14.1 T, the second-order susceptibility was found to be 3.4 × 10^-7 (SI unit) near the resonance condition.     

Investigation of hydrogen bond effects on the hyperpolarizability of 2-Aminopyridinium maleate (2APM) complex and determining the non-linear optical susceptibility of the molecular crystal of 2APM

2-Aminopyridinium maleate (2APM) is a recently discovered organic acid-base complex that crystallizes in a non-centrosymmetric space group Pc and hence has a nonzero second-order optical susceptibility. In 2APM the cation (aminopyridinium ion) is connected to the anion (maleate ion) through hydrogen bonds (N1-H10–O2 and N2-H12–O1), we have calculated the molecular properties of 2APM for varying strength of these hydrogen bonds. It is observed that the molecular hyperpolarizabilty varies for varying strength of these hydrogen bonds. These observations are interpreted in terms of the change in nature of the hydrogen bond interaction as its strength is varied. Macropscopic second-order optical susceptibility (d ₀) of 2APM is obtained using the calculated value of molecular hyperpolarizability and the reported crystal structure of 2APM. In order to study the influence of molecular packing on the macroscopic non-linear optical property of the crystal, susceptibility calculations are repeated for 2-methyl-4nitroaniline (MNA) crystal, which is a very well known non-linear optical organic crystal with an exceptionally high value of second-order optical susceptibility. A comparison between the non-linear optical property of 2APM and MNA crystals is given. Comparing the values of d ₀ of 2APM crystals with that of urea shows that the nonlinear optical response of 2APM crystals will be nearly 10 times that of a urea crystal.     

Manifestation of nano-sized effects in photoinduced nonlinear optics of CdI2–Cu layered single crystals

The infrared (IR) induced second harmonic generation in the thin CdI₂–Cu crystalline layers was discovered. With decreasing thickness of the CdI₂–Cu crystals up to several nanometers value of second-order nonlinear optical susceptibility d₁₄ (at wavelength λ=2.76 μm) for the output IR-induced SHG significantly increases. For the Cu content about 0.4% the output SHG signal achieves its maximum at the sample thickness below 2 nm. It is important that for the samples with larger film thickness the corresponding changes have substantially different properties. Limitation of the d₁₄ at the larger concentration is probably caused by formation of the Cu clusters limiting the enhancement of the hyperpolarizability for particular cluster as well as total nonlinear dielectric susceptibility.     

Raman spectroscopy of the BC3 phase obtained under high pressure and high temperature

A direct transformation of the g‐BC₃ phase to a new diamond‐like d‐BC₃ phase was observed in a diamond‐anvil cell (DAC) at high temperature, 2033 ± 241 K, and high pressure, 50 GPa. Analysis of the peak positions of the d‐BC₃, B₄C, α‐boron, and the boron‐doped diamond leads to the conclusion that the positions of the peaks of the d‐BC₃ are more similar to the peak pattern of the boron‐doped diamond rather than that of boron carbide, α‐boron. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of xylenol orange on the crystalline perfection,optical, piezoelectric and NLO behavior of unidirectionally grown imidazolium L-Tartrate single crystal

Pure and 0.1 mol% Xylenol orange (XO) doped Imidazolium L-tartrate (IMLT) nonlinear optical (NLO) single crystals were grown using Sankaranarayanan–Ramasamy (SR) method of uniaxial solution crystallization technique. The pure IMLT crystal is 100 mm in length and 15 mm in diameter. The doped IMLT crystal is 25 mm in length and 10 mm in diameter. UV–Vis-NIR spectrum shows that the pure and XO doped IMLT crystals' cut off wavelength is 235 nm. High-resolution X-ray diffraction (HRXRD) measurement and birefringence interferometry confirm that the SR method grown crystal has good crystalline perfection and optical homogeneity. The wavelength dependent refractive index and piezoelectric d₃₃ coefficient were measured. The difference refractive index (Δn) of (100) plane in parallel and perpendicular directions shows a strong dependence on wavelength. The dielectric constant, hardness and SHG conversion efficiency were also increased as a result of XO dye doping in IMLT crystal.     

Synthesis and nonlinear optical properties of branched pyrroline chromophores

New tricyanopyrroline (TCP) chromophores with rigid–flexible dendron were prepared for second‐order nonlinear optical (NLO) application. The chromophores were fully characterized using ultraviolet‐visible spectroscopy, nuclear magnetic resonance spectroscopy and mass spectrometry. Thermal gravimetric analysis (TGA) revealed that the chromophores had excellent thermal stability. Large λ_max and high solvate chromic effects revealed that the chromophores had large second‐order optical nonlinearity. The electro‐optic coefficients (r₃₃) were measured in the chromophores‐doped poly(bisphenol A carbonate) films at the fundamental wavelength of 1310 nm, and the highest γ₃₃ achieved was 217 pmV^?1. Copyright © 2010 John Wiley & Sons, Ltd.     

Dielectric and piezoelectric properties of PZT–silica fume cement composites

PZT–silica fume cement (PZT–SFC) composites were produced using PZT (at 50% and 60% by volume) and silica fume cement (cement containing silica fume of 5% and 10% by weight). PZT–Portland cement with no silica fume was also produced to allow comparison of the results. Dielectric constants of PZT–SFC composites are found to be higher than that of PZT–PC composite where ε_r value was found to increase with increasing SF content (ε_r values of composite with SF at 0%, 5% and 10% are 117, 125 and 178, respectively). PZT–SFC composites were successfully poled and d₃₃ results of PZT–SFC composites (d₃₃ = 18 pC/N) were found to be marginally higher than that of PZT–PC composite (d₃₃ = 17 pC/N). SEM micrograph also shows a dense matrix of SFC hydration product surrounding the PZT particles. From the results, these PZT–SFC composites are therefore promising materials for use in structural applications and should be ideal for high strength structures where SFC is used in the host structure.     

Dielectric and piezoelectric properties of manganese‐modified PbHfO3–PbTiO3–Pb(Mg1/3Nb2/3)O3 ternary ceramics with morphotropic phase boundary compositions

High piezoelectric and electromechanical properties were reported in the PbHfO₃–PbTiO₃–Pb(Mg_1/3Nb_2/3)O₃ ternary system with morphotropic phase boundary (MPB) compositions. This work focuses on the effect of MnO₂ addition on 0.8Pb(Hf_0.443Ti_0.557)O₃–0.2PMN (0.8PHT–0.2PMN) ceramics. It was observed that the Mn acceptor modification induced a “hardening” effect in 0.8PHT–0.2PMN, with decreased piezoelectric coefficients d₃₃ and dielectric loss tan δ and a significantly increased mechanical quality factor Q_m. Moreover, the 0.2 wt% MnO₂‐doped 0.8PHT–0.2PMN ceramics exhibited good piezoelectric and electromechanical properties with d₃₃, planar electromechanical coupling k_p and Q_m being on the order of 360 pC/N, 61% and 700, respectively, showing advantages compared to those of commercial hard PZT4 ceramics, which is attractive for high power applications. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Measurement of Second-Order Optical Nonlinear Coefficient from the Absolute Radiant Power of Parametric Fluorescence in LiI03

This work presents a new technique for the measurement of second-order optical nonlinear coefficients from the absolute radiant power of the parametric fluorescence emission. It is based on calibrated detectors regarded as secondary radiometric standards. This technique makes it possible to skip a number of problems usually encountered with standard techniques based on calibrated neutral density filters and reference sources of light at much higher power levels. We infer a value for the d₃₁ nonlinear coefficient of LiIO₃ from spectral measurements of the fluorescence power integrated over all solid angles, by denning the wavelength bandwidths with interference filters. Moreover, by performing the measurements on the ultraviolet and visible emission lines of an argon ion laser in the range from 351 to 488 nm, the wavelength dependence of d₃₁ is compared with the expected one obtained by Miller’s dispersion law.     

Optical second-harmonic generation of modulation doped Ga0.8Al0.2As film grown by molecular beam epitaxy

Absolute values of the second-order nonlinear susceptibility of modulation doped (100) Ga_0.8Al_0.2As are measured through a Q-switched Nd:YAG laser with self-calibrated power emanating in p-polarization. The angular variation of the reflecting second-harmonic wave agrees satisfactorily with the Bloembergen and Pershan theory. The nonlinear susceptibility of Ga_0.8Al_0.2As grown by MBE method is 20% larger than that of GaAs. A quasi-photon counting technique exploited in this experiment provides the possibility to detect the second harmonic reflecting coefficients as low as 10^-21cm²/watt.     

Zero-reflection metal slabs: A mechanism of light tunneling in metamaterials

Thick metals are nearly opaque due to high reflectance and the huge third-order nonlinear susceptibility of metals is hardly utilized. In the present paper, zero-reflection phenomena in a thick metal (M) slab covered with one-dimensional dielectric photonic crystals (PC’s) (CD) _n are studied in heterostructures M(DC) _n and sandwiched structures (CD) _n M(DC) _n . Visible-light tunneling modes can be realized in M(DC) _n or (CD) _n M(DC) _n in which the optical epsilon-negative medium (metal) is paired with the PC, which mimics a lossless optical mu-negative medium in the gap region. The transmittance as high as 33% and 38% are observed at wavelength of 589 nm for M = Ag, with thickness d=60.2 nm in a heterostructure and d=83.1 nm in a sandwiched structure, respectively. The transmittance is more than 200 times larger than that of a single Ag layer with the same thickness in the latter case. Possible applications on metal-based nonlinearity enhancement and optical absorber are also discussed.     

Thin films of arylenevinylene oligomers prepared by MAPLE for applications in non-linear optics

This paper discusses two arylenevinylene oligomers with optical nonlinear properties. Their trans molecular structure was confirmed by Fourier Transform Infrared Spectroscopy and Nuclear Magnetic Resonance. Second Harmonic Generation and two-photon fluorescence have been observed on Matrix Assisted Pulsed Laser Evaporation-deposited thin films. We have seen two local maxima in UV-Vis spectra and a red shift of the photoluminescence peak for carbazole-based oligomer, which can be correlated with a higher conformational flexibility and with strong polarization interactions in the solid state. Scanning Electron Microscopy and Atomic Force Microscopy images have revealed a grainy morphology of the film deposited on titanium and a higher roughness for carbazole-based oligomer. Second harmonic measurements have shown nearly equal values of the second-order nonlinear optical coefficient for the triphenylamine and carbazole-based oligomers for P_laser < 100 mW. z-Scan and x-scan representations of the carbazole-based oligomer film have shown strong two-photon fluorescence intensity inside the sample confirming a volume process, and a strong second harmonic at the surface of the sample determined by the surface morphology.