无零级衍射干扰的彩色数字全息研究

彩色数字全息研究中,用球面波为重建波及角谱衍射公式进行波前重建是一种有效的方法.然而,重建图像上通常伴有强烈的零级衍射干扰.本文通过理论分析,对波前重建过程作了重要改进.用改进后的方法进行彩色数字全息的实验研究表明,重建彩色图像的质量获得显著改善. 关键词： 彩色数字全息 波前重建 零级衍射干扰     

基于双芯光纤耦合器的梳状滤波器及其CO2激光调节

基于光纤耦合器的波长特性,分析了光纤耦合器作为梳状滤波器的光谱特性;将长度不同的双芯光纤(twin-core fiber,TCF)熔接在两根单模光纤(single mode fibors,SMF)之间,实验制得具有不同峰值波长间隔的基于双芯光纤耦合器的全光纤型梳状滤波器,其消光比可达25 dB. 首次使用CO₂激光对其进行光谱调节,调节导致光谱向长波方向漂移和消光比的变化. 这种调节是基于CO₂与光纤相互作用时的残余应力释放和熔融变形机理,使用氢载TCF可以在相同实验参数下得到更大的波长调节激光. 关键词： 双芯光纤耦合器 梳状滤波器 2激光')" href="#">CO₂激光 残余应力     

Large-scale synthesis and the roles of growth conditions on the formation of Zn2GeO4 nanorods

Large-scale Zn₂GeO₄ nanorods with a length of about 10 μm have been synthesized via a facile hydrothermal process in the absence of any surfactant. The synthesized nanorods are single crystals with a rhombohedral phase. The dependence on the growth conditions, such as reaction temperature, reaction time, compactness and GeO₂ concentration, of the formation, morphologies and sizes of the Zn₂GeO₄ nanostructures has been investigated. Proper selection and combination of the growth conditions are the key aspects to control the formation, morphologies and sizes of the Zn₂GeO₄ nanostructures. The nucleation and crystalline growth mechanism are proposed to explain the formation and growth of Zn₂GeO₄ nanorods. The photoluminescence spectrum of the Zn₂GeO₄ nanorods exhibits three fluorescence emission peaks centered at 421, 488 and 529 nm when the excitation wavelength is 235 nm.     

Ultracompact nonreciprocal optical isolator based on guided resonance in a magneto-optical photonic crystal slab

We design an ultracompact optical isolator with normal incident geometry that operates with a bandwidth that is substantial for a device of this size. For operation in a telecommunication wavelength of 1.55?μm, the thickness of the device is less than 1?μm and the device supports an operating bandwidth of 400?GHz over which the minimum contrast ratio exceeds 25?dB. Our design utilizes guided resonance in a photonic crystal slab to enhance magneto-optical effects, and exploits interference effects among multiple resonances to create desired transmission spectral line shapes.     

Picosecond pulses from a cryogenically cooled, composite amplifier using Yb:YAG and Yb:GSAG

A cryogenic Yb amplifier using two laser materials, Gd3Sc2Al3O12 and Y3Al5O12 (YAG), has been used to obtain 70 W average power at 5 kHz pulse repetition frequency; the output was compressed to 1.6 ps, compared with an input compressible to 1.4 ps. The gain broadening obtained by combining two media enables shorter pulses than using Yb:YAG alone but retains the power-scaling advantages of cryogenic Yb:YAG.     

Intense photoluminescence at 2.7 μm in transparent Er 3+:CaF2-fluorophosphate glass microcomposite

Er3+ doped CaF2-fluorophosphate (FP) glass microcomposites were produced by heat-treating the mixture of Er3+:CaF2 precipitate and FP glass powder above the melting temperature of the FP glass. The appearance of CaF2 crystallites in the resulting composites was confirmed by x ray diffraction. Despite the fact that the average diameter of the crystallites was around 10 μm as revealed by the micromorphology study, a transparent composite was obtained by matching the refractive index of FP glass to that of CaF2. Intense IR fluorescence at around 2.7 μm was observed in the composite, implying the composite would be a promising candidate for IR lasers and amplifiers.     

Four-dimensional flash trajectory imaging using time-delay-modulated range-gated viewing

We present a four-dimensional flash trajectory imaging method to image object trajectories over time in three-dimensional space. In the method, time-delay-modulated range-gated viewing with multiple exposures is presented so that the time evolution of object trajectories free from background interference is directly given without complicated image processing and the motion parameters of objects can be estimated. The method is demonstrated by a ball oscillating as a pendulum.     

Superhydrophobicity of silica nanoparticles modified with polystyrene

Polystyrene/silica nanoparticles were prepared by radical polymerization of silica nanoparticles possessing vinyl groups and styrene with benzoyl peroxide. The resulting vinyl silica nanoparticles, polystyrene/silica nanoparticles were characterized by means of Fourier transformation infrared spectroscopy, scanning electron microscopy and UV-vis absorption spectroscopy. The results indicated that polystyrene had been successfully grafted onto vinyl silica nanoparticles via covalent bond. The morphological structure of polystyrene/silica nanoparticles film, investigated by scanning electron microscopy, showed a characteristic rough structure. Surface wetting properties of the polystyrene/silica nanoparticles film were evaluated by measuring water contact angle and the sliding angle using a contact angle goniometer, which were measured to be 159° and 2°, respectively. The excellent superhydrophobic property enlarges potential applications of the superhydrophobic surfaces.     

Fabrication of CuO/T-ZnOw nanocomposites using photo-deposition and their photocatalytic property

CuO/tetrapod-like ZnO whisker (T-ZnOw) nanocomposites were successfully synthesized using a simple photo-deposition method. Some nanocomposites exhibit remarkably improved photocatalytic property, while the extents of the improvements vary with different Cu/Zn molar ratios and polyethylene glycol (PEG) concentrations. Moreover, it is found that excessively high Cu/Zn molar ratio or PEG concentration would reduce the photocatalytic property of the nanocomposites. A direct relationship between the morphology and the photocatalytic property of CuO/T-ZnOw was established and then analyzed by discussing the photocatalytic mechanism of the CuO/T-ZnOw nanocomposites.     

Correlation between microstructure and property of electroless deposited Pt counter electrodes on plastic substrate for dye-sensitized solar cells

Flexible Pt counter electrodes (CEs) were prepared on indium-doped tin oxide coated polyethylene naphthalate (ITO-PEN) substrate by electroless deposition. The correlation between the microstructure and the property of the Pt CEs was investigated. Results showed that isolated Pt nanoparticles were uniformly distributed on the ITO surface at a short deposition duration, and then grew with the deposition duration, leading to the interconnection of adjacent Pt nanoparticles. The interconnection of Pt nanoparticles was beneficial to the electrical property of the Pt CEs, while it was unfavorable to the electrocatalytic property of the Pt CEs. A microstructure model was proposed to explain the correlation between the microstructure and the property of the Pt CEs. In addition, the Pt CEs showed low charge transfer resistance (1.66-0.58 Ω cm²), which was comparable to that (1.16 Ω cm²) of the conventional sputtered Pt CE. The high electrocatalytic property of the electroless deposited Pt CEs makes the assembled DSCs present comparable energy conversion efficiency of the DSCs using sputtered Pt CE.