Investigation on the nonlinear optical properties of the DCNP/PEK-c guest–host polymer films

The polyetherketone (PEK-c) guest-host polymer thin films doped with 3-(1,1-dicyanothenyl)-1-phenyl-4,5-dihydro-1H-pryazole (DCNP) were prepared. The polymer films were investigated with in situ second-harmonic generation (SHG) measurement. The corona poling temperature was optimized by the temperature dependence of the in situ SHG signal intensity under the poling electric field applying. The temporal and temperature stability of the second-order properties of the poled polymer film were measured by the in situ SHG signal intensity probing. The second-order NLO coefficient L₃₃⁽²⁾=32.65 pm/V at 5=1064 nm was determined by using the Maker fringe method after poling under the optimal poling condition. The dispersion of the NLO coefficient of the guest-host polymer system was determined by the measured value of L₃₃⁽²⁾ at 1064 nm and the two-level model.     

Broadband high-energy mirror for ultrashort pulse amplification system

We report a broadband high-energy mirror for TW-class chirped-pulse amplification of ᄺ-fs pulses. This mirror consists of broadband coatings and optimized high-damage-threshold coatings for decreasing the intensity on the broadband coatings. It is important to optimize the number of high-damage-threshold coatings so that high damage-threshold and relatively low dispersion are traded off against each other. The bandwidth of this mirror ((5겨 nm at 5₀꼀 nm) is almost equivalent to that of a commercial broadband mirror, and the damage threshold of this mirror is almost equivalent to that of a commercial high-energy mirror. This mirror can withstand chirped pulse laser beam's with high fluence (>1 J/cm²) and wide spectra (153 nm FWHM) in practice.     

Thermal tuning of a fixed Bragg grating for IR light fabricated in a LiNbO3:Ti channel waveguide

We investigate a thermally tunable integrated narrow-bandwidth interference filter for light in the infrared wavelength region around 5=1550 nm fabricated in a channel waveguide in lithium niobate. The filter is based on a holographically recorded and thermally fixed refractive-index Bragg grating. The device is connected to optical single-mode fibers and works polarization-independent. We measure a peak reflectivity of 95% and a linewidth (FWHM) of 0.09 nm. By temperature-controlling the peak wavelength of the filter is tuned. For the linear thermal expansion coefficient of lithium niobate along the c axis the value !₃₃=(4.5ǂ.5)᎒^-6 K^-1 is obtained. Permanent illumination of the filter with incoherent light allows us to adjust the peak reflectivity. Dedicated to Prof. K. Ringhofer on the occasion of his 60th birthday.     

Fe:LiNbO3全息图热定影及H+浓度的影响

应用光折变效应动力学方程,导出了在Fe:LiN_bO₃中对光折变全息图热定影所需的最小H⁺浓度,以及H⁺浓度与光栅空间频率的关系.应用光谱比较法测量了不同样品的H⁺浓度值.得出了进行有效热定影的H⁺浓度范围.完成了Fe:LiN_bO₃全息存储和热定影实验.获得了100h连续无损读出的良好热定影实验结果.     

KTiOPO4, KTiOAsO4, and KNbO3 crystals for mid-infrared femtosecond optical parametric amplifiers: analysis and comparison

We have designed a simple mid-IR femtosecond OPA seeded by a white-light continuum and delivering very stable, largely tunable and energetic output pulses. This OPA requires fewer than 200 7J of 120-fs Ti:sapphire pump pulses as energy. This system allowed us to experimentally compare the performances of potassium crystals (KTP, KTA, and KNbO₃) for the generation of up to 100-fs Fourier-transform-limited pulses tunable in 1-4.6 7m mid-IR wavelengths.     

Epitaxial growth of non-c-oriented ferroelectric SrBi2Ta2O9 thin films on Si(100) substrates

Epitaxial SrBi₂Ta₂O₉ (SBT) thin films with well-defined (116) orientation have been grown by pulsed laser deposition on Si(100) substrates covered with an yttria-stabilized ZrO₂ (YSZ) buffer layer and an epitaxial layer of electrically conductive SrRuO₃. Studies on the in-plane crystallographic relations between SrRuO₃ and YSZ revealed a rectangle-on-cube epitaxy with respect to the substrate. X-ray diffraction pole figure measurements revealed well-defined orientation relations, viz. SBT(116)SrRuO₃(110)YSZ(100)Si(100), SBT[110]SrRuO₃[001], and SrRuO₃[111]YSZ[110]Si[110].     

Averaging scheme for atomic resolution off-axis electron holograms

All micrographs are limited by shot-noise, which is intrinsic to the detection process of electrons. For beam insensitive specimen this limitation can in principle easily be circumvented by prolonged exposure times. However, in the high-resolution regime several instrumental instabilities limit the applicable exposure time. Particularly in the case of off-axis holography the holograms are highly sensitive to the position and voltage of the electron-optical biprism. We present a novel reconstruction algorithm to average series of off-axis holograms while compensating for specimen drift, biprism drift, drift of biprism voltage, and drift of defocus, which all might cause problematic changes from exposure to exposure. We show an application of the algorithm utilizing also the possibilities of double biprism holography, which results in a high quality exit-wave reconstruction with 75 pm resolution at a very high signal-to-noise ratio.     

Dependence of functional properties on processing in sol-gel (Pb,La)TiO3 thin films

Pb_0.88La_0.08TiO₃ films were processed on Si-based substrates by a diol-based sol-gel route from solutions with variable content of PbO excess. Crystallisation was performed at heating rates of 10 °C min^-1 and higher than 500 °C min^-1 (rapid heating). The pyroelectric coefficient was measured after poling the samples by two methods: applying a sinusoidal wave and applying a train of square pulses, with the latter showing a higher poling efficiency. The piezoelectric d₃₃ coefficient was determined by double-beam interferometry. Strain vs. field measurements provided evidence of 90° domain orientation in these films. Those crystallised at 10 °C min^-1 showed the highest functional properties (%=1.7᎒^-2 7C cm^-2 K^-1 and d₃₃=57 pm V^-1). This is a consequence of the higher stability of the 90° domains oriented during poling, caused by the lower tensile stress arising during preparation. The voltage responsivity of these films also benefited from the lower permittivity arising from their higher porosity. These films are good candidates for applications in infrared detectors and microelectromechanical devices.     

Compact interrogator for fiber optic Bragg sensors based on an acousto-optic filter formed by photonic crystal rows of air holes

Fiber optic sensors are typically used with expensive tunable lasers or optical spectrum analyzers for wavelength interrogation. We propose to replace the tunable laser by a broadband optical source incorporated with a novel thin linewidth acousto-optic tunable filter. It utilizes optical beam expanders constituted by photonic crystal rows of air holes in LiNbO(3) waveguide. A new design is numerically studied for a short structure (with 32 photonic crystal rows) by a two-dimensional finite-difference time-domain method. Extrapolation of these results to larger structure sizes (about 1 cm) demonstrates the possibility to develop compact interrogators with 0.4 pm wavelength resolution and 40 nm tunable range around 1550 nm.     

MSLM调制组件的电光性能

对设计并制作的[M_gF₂+(ZrO₂/SiO₂)]膜系·LiNbO₃·ITO/玻璃结构的MSLM用调制组件的综合电光性能进行了实验测定。结果表明,其反射半波电压V_πR为1.2kV±0.1kV,反射率达99%,峰值次级电子发射系数为5.8。用其制作的光导址MSLM具有良好的功能与性能。     

Computer-generated holograms from 3D-objects written on twisted-nematic liquid crystal displays

In order to optimize computer-generated holograms (CGHs) for three-dimensional objects, an extension of the well known Gerchberg-Saxton algorithm is used. Optical reconstructions using an electrically addressed twisted-nematic liquid crystal display are presented. For arbitrary CGHs, reconstructing 3D-objects, we will discuss the problems and solutions associated with periodic replication of holograms.     

Simple determination of Na2 scattering lengths using observed bound levels at the ground state asymptote

A simple model is developed to determine a scattering length from the experimental values of the energy of the last, least bound, vibrational levels of the ground state, either ¹S_g⁺^1\Sigma _g^{+} or ³S_u⁺^3\Sigma _u^{+},of an alkali dimer. It is based on an extrapolation of the positions of the few outermost nodes of the bound vibrational wave functions towards the dissociation threshold. It uses the asymptotic part of the molecular potential only. The method is applied to recently measured levels at the asymptote (3s+3s) of Na₂. We obtain precise values for the two scattering lengths respectively associated to the dissociation limits F₁=F₂=1,F=2 (55.1±\pm 1.6 a₀) and F₁=F₂=1,F=0 (50.0±\pm 1.6 a₀); the first value corresponds to the a_1,-1 scattering length usually considered in cold collisions. The extrapolation procedure is also applied to Li₂, using existing experimental data.     

The effect of a photovoltaic field on the Bragg condition for volume holograms in LiNbO3

Experimental and theoretical studies of the photovoltaic shift in the position of the diffraction efficiency maximum of holograms recorded in LiNbO₃ for the case of optimal electric field multiplexing are described. The experimental data are explained using a model in which the bulk photovoltaic field is excited in a crystal that is electrically connected with a low loading resistance. We suggest that the surface conductivity of the crystal can play an important role in the formation of this effective loading resistance. Received: 29 November 2000 / Revised version: 9 February 2001 / Published online: 27 April 2001     

Holographic angle multiplexing combined with peristrophic multiplexing in a photorefractive LiNbO3 crystal

We have investigated angle multiplexing combined with peristrophic (rotational) multiplexing in a photorefractive LiNbO₃ crystal of cylindrical shape. The peristrophic multiplexing was achieved by rotating the recording medium while the angle multiplexing, by varying the incident angle of the reference beam. Angle multiplexing in synchronization with rotation of the sample made it possible to continuously record and retrieve holograms. In the combined multiplexing, holograms were stored at different peristrophic positions and thus their angular selectivity could be much improved in comparison to that of only angle-multiplexed holograms. The theoretical angular selectivity was derived, along with its dependence on the sample rotation. The experimentally measured selectivity was in agreement with the theoretical one. The angular selectivity of angle-multiplexed holograms was measured to be 0.03° in the absence of sample rotation and it became less than 0.0075° with a sample rotation by 5.4°.     

Temperature-tuned difference-frequency mixing in periodically poled KTiOPO4

4 (PPKTP). We generated 12 μW of radiation tunable around 1.6 μm by difference-frequency mixing of the outputs of a frequency-doubled Nd:YLF laser at 523 nm (240 mW) and a tunable Ti:sapphire laser near 760 nm (340 mW). A temperature tuning rate of 0.73 nm/°C for the generated wavelength and a FWHM temperature acceptance bandwidth of 6.9 °C cm was observed. The effective d₃₃ coefficient was estimated to be ∼5 pm/V. Received: 02 September 1998     

Facile ultrasound-assisted grafting of silica gel by aminopropyltriethoxysilane for aldol condensation of furfural and acetone

This work focuses on the development of a simple method to prepare heterogeneous catalysts with tunable basicity and stability for aldol condensation of furfural and acetone. Silica gel was grafted by aminopropyltriethoxysilane (APTES) with 20, 30, 40 and 50 wt. % of APTES using probe-type ultrasonicator with a power of 130 W and a frequency of 20 kHz. The grafted samples were studied by XRD, SEM, N₂ sorption, FTIR, XPS, CHN and TG analysis, and CO₂-TPD. The sonication facilitated the bond formation between APTES and the silica gel with less pore blocking than the conventional grafting method. The basicity of the samples was tunable with the quantity of APTES loading. The grafted samples were active catalysts for aldol condensation between furfural and acetone at 60 °C. The catalyst with 30 wt. % APTES grafting (30APS-U) provided a nearly complete furfural conversion and high furfurylbutenone selectivity. The conversion and selectivity increased with time and reached the highest values at 24 h. Thus, the catalysts with tunable basicity prepared by ultrasound-assisted grafting of silica with various APTES amounts were effective in furfural valorization.     

Electrically controlled diffraction of light by reflection holograms in an LiNbO3 crystal

A theoretical and experimental investigation is made of the electrical selectivity of reflection volume holograms recorded in a LiNbO₃ crystal using a near-optimum geometry. An analysis is made of the factors limiting electrical multiplexing. Fiz. Tverd. Tela (St. Petersburg) 40, 1038–1041 (June 1998)     

紫光至红光敏感的多波长复用全息存储材料

制备了一种对紫光至红光波段敏感的光致聚合物全息存储材料,用476 nm、488 nm、496 nm、514.5 nm及632.8 nm五种波长曝光对其进行光全息性能的研究.研究表明,该材料在各种波长下的最大衍射效率均不低于45%,曝光灵敏度大于4.22×10－3 cm2·mJ－1,折射率调制度高于1.62×10－4,光栅频率接近3 000 lp/mm等.     

Influence of the substrate voltage on the random telegraph signal parameters in submicron n-channel metal-oxide-semiconductor field-effect transistors under a constant inversion charge density

In this paper, the impact of the substrate bias U_BS on the parameters of a repulsive random telegraph signal in an n-channel metal-oxide-semiconductor field-effect transistor is studied. Particular attention is paid to the variation of the capture time constant F_c with the channel current I in linear operation. It is shown that the strong reduction of F_c with I can be explained by the Coulomb blockade effect. The corresponding Coulomb energy (E of the charged-near-interface oxide trap is shown to be a strong function of the substrate bias. From the analysis of the experimental results considering surface quantization effects follows that the variation of (E with U_BS is caused by the change in both the inversion layer surface charge density N_s and in the surface electric field F_s that influences the distance between the centroid of the inversion layer and the interface. In fact, it will be demonstrated that (E can be expressed in function of a single parameter (N_sF_s²). Finally, the impact of the substrate bias on the other parameters, i.e., the amplitude (I, the emission time constant F_e and the distance d of the trap from the interface, will also be addressed.