N2O脉冲高压直流放电的光谱研究

建立了一套产生瞬变物种的脉冲高压放电及其光谱探测的分子束装置,该装置的放电部分可在最高10kV电压条件下长期稳定工作,在数据采集中利用软件实现了取样积分器的功能,并且可以进行多通道数据的同时采集。利用此装置在几Pa压力下对N2O脉冲高压直流放电过程进行了研究,对得到的N2O (A~2Σ —~X2Πi)发射谱进行了标识,由振动光谱的强度得到了N2O ~A态的相对振动布居,和以往的研究结果相比,得到的N2O ~A态更偏离Bolzmann分布,产生的~A态是初生态。     

Study on a novel phase-recovering algorithm for partial intensity saturation in digital projection grating phase-shifting profilometry

The phase error and its periodic behavior caused by the partial intensity saturation of fringe patterns in the digital projection grating phase-shifting profilometry are studied. A saturation coefficient K is defined to describe the saturation degree of the fringe patterns projected on a measured object. The distribution of the phase error is analyzed through a simulation method. Moreover, a novel phase-recovering algorithm is studied to resolve the phase error issue introduced by the partial saturated fringe patterns. The real phase can be recovered by the unsaturated intensity values. A series of results corresponding to different degrees of saturation defined by K are given to prove the validity of the proposed algorithm.     

Spectral anomalies of pulsed Hermite-cosh-Gaussian beams focused by an aperture lens

The spectral behaviors of pulsed Hermite-cosh-Gaussian (HChG) beams focused by an aperture lens are studied. The propagation equation for the power spectra of pulsed HChG beams focused by an aperture lens is derived and used to study the spectral anomalies of pulsed HChG beams in the focused field. Numerical results are given to illustrate the dependence of spectral anomalies behavior on the pulse parameter and truncation parameter. The potential applications of spectral anomalies of ultrashort pulsed beams in information encoding and information transmission are considered.     

Focusing properties of Gaussian beam with mixed screw and conical phase fronts

Vector diffraction theory is employed to investigate the focusing properties of the Gaussian beams with mixed screw and conical phase fronts. Numerical simulations show that the Gaussian beams with screw-conical phase fronts are different from both the ordinary Laguerre-Gaussian beams and the higher-order Bessel beams. Rather than forming the ring-shaped intensity distributions characteristic of optical vortices, focusing the Gaussian beams with screw-conical phase fronts produce non-symmetric spiral intensity distributions at the focal plane. The intensity distribution forms a counter-clockwise non-symmetric screw path around the focus. The rotation of intensity distributions was observed in the focal plane. The gradient force patterns of these beams focused with high NA are also investigated. The results show that the gradient force pattern shape depends principally on parameter topological charge n of the phase distribution. The gradient force pattern expands with increase in the parameter m of the phase distribution. Therefore, one can change the topological charge n or the parameter m of the phase mask to construct the tunable optical trap to meet different requirements. Its potential application might include rotational positioning of particles and accumulation of smaller non-symmetric particles towards the focus.     

Nanoscale patterning of functional perovskite-type complex oxides by pulsed laser deposition through a nanostencil

We present studies on parallel nanoscale patterning of piezoelectrics/ferroelectrics via deposition through a nanostencil. Unlike other processes reported for oxide nanostructuring, we selectively deposit the material, directly, by interposing a nanosieve between the substrate and the deposition source. We show that this selective deposition can be realized even with materials as complex as perovskite oxides, both at room temperature and at high temperature. We elaborate on and analyze the performance of the nanostenciling approach for the growth of barium titanate BaTiO₃ on strontium titanate SrTiO₃(1 0 0). The patterned structures of ferroelectric materials are characterized by X-ray diffraction and imaged locally by scanning probe microscopy in piezoresponse mode to individually probe their functionality.     

Oxygen reduction activity of N-doped carbon-based films prepared by pulsed laser deposition

Carbon-based films with nitrogen species on their surface were prepared on a glassy carbon (GC) substrate for application as a non-platinum cathode catalyst for polymer electrolyte fuel cells. Cobalt and carbon were deposited in the presence of N₂ gas using a pulsed laser deposition method and then the metal Co was removed by HCl-washing treatment. Oxygen reduction reaction (ORR) activity was electrochemically determined using a rotating disk electrode system in which the film samples on the GC substrate were replaceable. The ORR activity increased with the temperature of the GC substrate during deposition. A carbon-based film prepared at 600 °C in the presence of N₂ at 66.7 Pa showed the highest ORR activity among the tested samples (0.66 V vs. NHE). This film was composed of amorphous carbons doped with pyridine type nitrogen atoms on its surface.     

Scanning laser microscope for imaging nanostructured superconductors

The nanofabrication of superconductors yields various interesting features in superconducting properties. A variety of different imaging techniques have been developed for probing the local superconducting profiles. A scanning pulsed laser microscope has been developed by the combination of the XYZ piezo-driven stages and an optical fiber with an aspheric focusing lens. The scanning laser microscope is used to understand the position-dependent properties of a superconducting MgB₂ stripline of length 100 μm and width of 3 μm under constant bias current. Our results show that the superconducting stripline can clearly be seen in the contour image of the scanning laser microscope on the signal voltage. It is suggested from the observed image that the inhomogeneity is relevant in specifying the operating conditions such as detection efficiency of the sensor.     

采用OFDM信号作为标记的光分组交换方案

以光正交频分复用信号作为光标记,利用两个不同波长的光载波分别经过强度调制,产生了10 Gb/sOOK光载荷和2.5 Gb/sOFDM光标记。测得了光分组信号经光纤传输前后接收载荷的眼图和标记的星座图以及误码率曲线,结果表明:经过40 km光纤传输后,载荷与标记的功率代价分别为1dB和0.5dB。     

自由空间中超短脉冲光束的非傍轴效应分析

在应用时间与空间傅里叶变换的基础上, 运用泰勒展开的方法, 得出了一种对多周期超短脉冲光束进行非傍轴修正的方法, 并将其应用于脉冲高斯光束．与数值结果的比较表明, 对于束宽在波长量级的脉冲光束, 二阶修正已经很接近非傍轴精确解, 并在例子中观察到：由于超短脉冲光束中时空耦合效应的存在, 脉冲的时间分布将会影响修正的空间分布．     

多晶硅表面周期性微结构的激光制备与性能研究

为了减小多晶硅表面入射光的反射率,提高太阳能电池的光电效率,利用紫外纳秒激光器在多晶硅表面制备不同深度、不同间距的微凹坑点阵绒面,研究织构形貌对反射率及光电转换效率的影响。通过激光频率的改变实现微凹坑深度的变化,通过微凹坑排布方式的改变实现微凹坑间距的变化;使用光纤光谱仪测量多晶硅表面反射率并通过激光共聚焦显微镜观察微凹坑形貌;在PC1D软件中建立多晶硅入射光反射模型并模拟不同点阵间距下的多晶硅短路电流和开路电压,计算光电转换效率和填充因子。研究表明,不同频率(300 kHz、200 kHz、150 kHz、50 kHz)和点阵排布方式(300×300、310×310、350×350、400×400)对多晶硅表面的反射率和光电转换效率影响显著,随着频率增大,多晶硅试样反射率先减小后增加最后保持稳定;随着点阵排布密集程度增加,多晶硅试样光电转换效率逐渐提高。实验结果显示当激光频率为150 kHz,点阵分布为400×400时,多晶硅表面微凹坑成型较好,表面平均反射率为3.32%,多晶硅电池的效率为18.80%,相较于未制绒多晶硅电池提高25.9%。