Development of novel flexible black silicon

We report a new type of black silicon: flexible black silicon. A silicon-on-insulator (SOI) wafer is irradiated by automatically scanning a femtosecond laser and then split by etching out the SOI silica middle layer. Large-area, uniform micro spikes on the surface of a very thin flexible silicon layer are obtained. The black silicon shows good flexibility and optical properties. The absorption spectrum of the flexible black silicon is as high as 97% in the visible and insensitive to the change of the incident angle of the light, which makes it a potential good candidate as an absorber for the solar-thermo generator.     

Wave optics simulation approach for high-power laser beam combination

A numerical wave optics approach for simulating multiplex super Gaussian beam combination in high-power laser facility is presented. The approach involves the application of a sequence of random phase screens and von Karman turbulence phase to an initial beam field and the summation of the intensity results. The analytical and numerical calculation results have been given to illustrate the properties of the resulting far-field pattern after coherent, incoherent and spatially coherent combination, and some of that are compared with experimental results. The approach can be used for modeling and evaluating applications such as high-power laser shooting that might utilize different beams combining approach.     

Controlling of symmetric and asymmetric mode coupling in long-period fiber gratings singe-side induced by long-pulse CO2 laser

We report a simple fabricating approach to control the mode couplings in long-period fiber gratings (LPFGs) through side exposing fiber to long-pulse-10.6-μm laser from a cheap, internally modulated CO₂ tube. By tuning focused-spot size on fibers, not only circularly symmetric mode coupling but also asymmetric mode couplings can be effectively achieved. Simulation of mode profiles in grating cross-section with Finite Element Method (FEM), and LPFG-cladding etching experiment with hydrofluoric acid (HF), support our explanation that asymmetric mode coupling in LPFGs depends on local refractive-index (RI) change within an azimuthally thin cladding layer, resulted from large-spot method induced deep melt flow on fiber surface during CO₂ laser irradiation.     

Study on the rewritability of bisazobenzene-containing films in optical storage based on two-photon process

In this paper, we use a two-photon technique to record data points on bisazobenzene-containing films. The recording data points are evidently polarization dependent. It is found that the recording data points can be erased by the linearly polarized light whose polarization direction is perpendicular to that of the recording beam and then, in the same region, new data can be rewritten after erasing. In addition, the recorded data can also be erased completely by the circularly polarized light. Compared with linearly polarized beam, the circularly polarized light is a better choice for erasure as no main orientation is regained after erasing rather than reorientation.     

Design and tolerance analysis of optical interleaver based on retardant crystals

A set of recursion equations was developed for the design of an optical interleaver based on retardant crystals and a third-order optical interleaver with maximally flat passband was designed accordingly. The fabrication tolerance for the retardant crystals was simulated based on crosstalk consideration. Given crosstalk requirement of −25 dB, the tolerance for the crystal thickness and axis orientation was obtained as 0.91 μm and 0.51°, respectively.     

电化学沉积金属铜的分形枝晶生长控制与性能

 以CuSO_{4/sub>为前驱体,HCl为添加剂,采用电化学沉积方法,在室温条件下制得了μm级、面心立方结构分形铜的枝状晶体,研究了铜离子浓度、硫酸浓度、电流密度、沉积时间、氯离子浓度等实验参数对分形枝状铜晶体尺寸、结构的影响。结果表明：硫酸的浓度对铜沉积物结构无明显影响;随着Cu^{2+/sup>浓度的不断增大,铜沉积物的分形效果越来越明显;增大电流密度（0.4～1.6 A·cm-2/sup>）,铜沉积物由致密向多分枝的开放型转变;延长沉积时间（大于等于5 min）,可获得含大量次级分枝铜的晶体;适当增加盐酸用量（0.05～0.20 mol/L）,铜沉积物枝晶尺寸显著减小。最后讨论了分形枝晶铜在碱性条件下氧化甲醇的电化学性能。}}     

高斯-谢尔模型光束通过杨氏双缝衍射后的解析传输公式

 通过将杨氏双缝窗口函数表示为复高斯函数叠加的方法,从Collins公式出发推导出了高斯-谢尔模型(GSM)光束通过杨氏双缝和ABCD光学系统后光强的近似解析表达式。利用该公式作了数值计算,通过与Collins公式计算结果进行比较,确定了该公式的适用范围,研究了相干长度和双缝中心遮拦比对解析公式适用范围的影响,并对该公式的应用前景作了展望。     

平顶高斯超短脉冲激光的时间部分相干性对相干合成的影响

 利用准单色光干涉理论,计算了2×2平顶高斯超短脉冲激光在远场的干涉图样,分析了激光的时间部分相干性及其存在束间相位差时对相干合成的影响。计算结果表明,当单路激光输出光束线宽小于100 nm时,理想波前的远场光斑图样和峰值光强基本保持不变,当光束线宽大于100 nm时,干涉减弱衍射效应逐渐增强;光束间存在相位差时,时间部分相干性将破坏远场图样随束间相位差的周期性变化,相位差越大干涉越弱;当超过相干长度时,则为非相干合成,但1/6倍相干长度范围内,仍可视为较理想的相干合成,此时焦斑的斯特列尔比大于0.9,对超短脉冲的相干合成影响可忽略。     

Mn-Cu合金成分对去合金化法制备纳米多孔铜的影响

 采用电弧熔炼制备出前驱体Mn-Cu合金,在稀盐酸溶液中自由腐蚀去合金化,制备出具有双连续结构的纳米多孔铜。研究了前驱体合金的成分对纳米多孔铜微观结构及Mn的选择性腐蚀程度的影响。结果表明：前驱体Mn-Cu合金的Cu原子分数为43%时,其去合金化受到抑制,存在明显的未完全去合金化的岛状结构;前驱体Mn-Cu合金的Cu原子分数为32%～23%时,可完全去合金化,形成平均孔径尺寸为20～100 nm,平均系带尺寸为30～80 nm,具有双连续结构的纳米多孔铜;前驱体Mn-Cu合金的Cu原子分数低至20%时,去合金化后存在大量裂纹,形成纳米颗粒聚集体。纳米多孔铜中存在少量的残余Mn,残余Mn的原子分数随着前驱体合金Mn原子分数的增高而降低。实验表明腐蚀液浓度对纳米多孔铜形貌也存在影响。     

缩水甘油胺型聚氨酯胶粘剂的性能研究北大核心CSCD

采用商品化SKE-1型环氧树脂对自制聚氨酯预聚体(NCOPU)进行封端,制备了缩水甘油胺型聚氨酯(GAPU),并用傅里叶-红外光谱(FT-IR)对其结构进行表征,用在线FT-IR监控间苯二甲胺固化GAPU过程,用差示量热扫描(DSC)研究其相分离,用扫描电镜(SEM)观察固化物的表面微观形貌,用热重(TG)分析固化物的热力学稳定性。探讨了聚丙二醇(PPG)分子量的大小、不同质量分数的SKE-1对NCOPU封端及不同种类的固化剂对GAPU固化物力学性能的影响。研究表明:在60℃时用间苯二甲胺固化GAPU,2h即可固化完全,固化物热稳定性能良好,其外推起始分解温度为248.3℃,5%的分解温度为282.6℃。GAPU固化物的力学性能随着GAPU的环氧值减小而减小,在室温以上力学性能下降,在-196℃力学性能增加,其环氧值为0.153,在-196℃的拉伸剪切强度最佳,为16.11MPa。