Cavity phase matching via an optical parametric oscillator consisting of a dielectric nonlinear crystal sheet

We experimentally demonstrate cavity phase matching for the first time using a sheet optical parametric oscillator which is made of an x-cut KTiOPO(4) crystal sheet. This microcavity presents 220 kW peak power capability for near-frequency-degenerate parametric outputs with up to 23.8% slope efficiency. It also features unique spectral characteristics such as single-longitudinal-mode and narrow linewidth. These attractive properties predict broad applications of such a mini-device, such as terahertz generation, photonic integration, spectroscopy, and quantum information, etc.     

Phase transitions in shear-induced segregation of granular materials

We computationally study shear-induced segregation of different-sized particles in vertical chute flow. We find that, for low solid fractions, large particles segregate toward regions of low shear rates where the granular temperature (velocity variance) is low. As the solid fraction increases, this trend reverses, and large particles segregate toward regions of high shear rates and temperatures. We find that this is a global phenomenon: local segregation trends reverse at high system solid fractions even where local solid fractions are small. The reversal corresponds to the growth of a single enduring cluster of 30%-60% of the particles that we propose changes the segregation dynamics.     

Application of the two-mode squeezed coherent state representation in deriving generalized optical Collins formula

We propose a new two-mode squeezed coherent state representation |z₁, z₂〉_g which is characteristic of the correlation between the squeezing and the displacement. Based on it and using the technique of integration within an ordered product of operators we obtain a generalized two-mode Fresnel operator (GTFO), which is an image of the mapping from (z₁, z₂) to in |z₁, z₂〉_g representation. The matrix element of GTFO in the coordinate representation leads to a generalized two-dimensional Collins formula (Huygens-Fresnel integration transformation describing optical diffraction) in entangled form.     

Design of different bandwidth dispersive mirrors

Dispersive mirrors in the wavelength range of 960–1110 nm, 700–900 nm, 950–1150 nm, 600–900 nm, 900–1200 nm, 600–1000 nm and 550–1050 nm are designed, respectively. From the design results, we analyse the choice of material and the approach to dispersion compensation. Furthermore, along with the increase of bandwidth, interaction between group delay dispersion (GDD) oscillation and high reflectivity, and influence of bandwidth on both GDD ripple and reflectivity are discussed.     

基于驻留时间补偿的抛光误差控制方法

 针对计算机控制光学表面成形中光学表面存在中高频误差的问题,提出了一种基于驻留时间补偿的有效控制方法。分析了抛光误差的形成机理和影响因素,对系统的误差影响因素进行分类和定量描述,构建了抛光过程中磨损影响因子、浓度变化影响因子和系统影响因子。基于各影响因素的影响因子对抛光驻留时间的求解函数进行了修正,提出采用离散最小二乘法对修正的函数求解驻留时间。研究表明：这种补偿方法能提高计算机控制光学表面成形技术中加工模型的精度,减小光学表面的残余误差。     

半导体制冷片制作的高能激光靶屏

 为了用热图法测量高能激光强度的时空分布,设计了将半导体制冷片作为激光靶屏的测量方案。研制了由16个50 mm×50 mm的制冷片组装成的总面积为200 mm×200 mm、总制冷功率超4 800 W的靶屏, 屏四周安装了8个红外标定物用于校正红外图像的畸变。理论上用热传导方程建立了激光辐照半导体制冷片靶屏的加热模型;数值模拟了屏表面温度分布同光强分布的关系,论证了氧化铝陶瓷材料制成的半导体制冷片作为高能激光靶屏的可行性,以及制冷片的制冷功能对测试性能的改善;通过实验验证了研制的靶屏测量光强是可行的。     

X波段2维金属光子晶体的加速结构

 光子晶体加速结构能够有效地阻尼高频率加速管中的尾场,对高能加速器中因尾场引起的束流不稳定性起到抑制作用。探索了X波段2维金属光子晶体微波加速结构的研制方法,用机械加工的方式制作了较高品质因数的2维光子晶体结构谐振腔。理论计算表明,在光子晶体结构谐振腔外围放置吸波材料,可有效地吸收加速结构中的类TM11偶极模等高次模,而对加速主模类TM01模影响较小。设计和制作了工作频率为11.42 GHz,由4个腔构成的X波段2维金属光子晶体行波加速器,实验结果与数值模拟计算值吻合较好。     

轴向分区双频磁绝缘线振荡器的数值模拟

 为了便于模式变换器的设计,达到双频微波都能集中辐射的目的,提出一种轴向分区的双频磁绝缘线振荡器,该器件束波互作用区为中间隔开、两端不同周期、不同深度的慢波结构,使电子在上下游与不同频率特性的慢波结构进行束波互作用,得到稳定的双频微波输出。使用2.5维全电磁粒子模拟软件进行数值模拟,在工作电压450 kV,电流40 kA条件下输出微波功率为1.4 GW,功率效率约为7%,输出的微波频率分别为1.25 GHz和1.65 GHz,两者频谱幅度相差约为1.5 dB,模式为TEM模。     

Widely tunable amplified spontaneous emission of Pyrromethene-650-doped nematic liquid crystal

We study amplified spontaneous emission of Pyrromethene-650-doped nematic liquid crystal deposited onto quartz and glass substrates. We prepare samples with different dye-doped concentrations pumped with a Nd:YAG laser at 532 nm. With an applied electric field, a tuning range of the amplified spontaneous emission of more than 20 nm was realized in each sample due to changing the effective refractive index of the nematic-liquid-crystal layer caused by the reorientation of nematic-liquid-crystal molecules. We show that there exist a threshold voltage and a saturation voltage for all the samples. With the increase in the dye-doped concentration, the peak wavelength of the amplified spontaneous emission has a red shift of about several nanometers.     

TiO<Subscript>2</Subscript> nanotube height effect on the efficiency of dye-sensitized solar cells

Performance of dye-sensitized solar cells (DSSCs) based on TiO₂ nanotubes (NTs) filled with TiO₂ nanoparticles (NPs) was studied as a function of NT height (h). The NT height was varied in the range of 1.5–7.0 μm, while the NT diameter was kept constant at ~80 nm. The studies showed that DSSC efficiency, current density, and fill factor linearly increased with h and ranged in 1.76–6.5%, 3.62–13.2 mA/cm², and 0.66–0.76, respectively, within the h range studied. The electrochemical impedance spectroscopy was also performed to study DSSC electron transport properties. Based on both photovoltaic and electrochemical impedance spectroscopy data, the results were explained as being due to the increased dye loading that led to higher light-harvesting efficiency.