A neutron polarization analysis study of Ce2Fe17 in its paramagnetic phase

Spin-flip (paramagnetic) scattering and neutron depolarization studies were performed on Ce₂Fe₁₇ in its paramagnetic phase on the Dhruva neutron polarization analysis spectrometer. The absence of normalQ dependence of the scattered spin flip intensity shows that Ce₂Fe₁₇ is not a normal paramagnetic and there exist superparamagnetic clusters of sufficiently large dimensions (～100Å). The observed neutron depolarization gives an indication of the dynamics of these Ce₂Fe₁₇ superparamagnetic clusters.     

Spherical gravitational collapse with photon emission and a generalized Schwarzchild interior solution

The general dynamical equations for perfect fluid filled spheres with an outward flux of photons are derived. The vital role played by the energy density of the free gravitational field in accelerating photon production has been emphasized. It is pointed out that even when the material energy density is finite, the energy density of the free gravitational field can take infinitely large values resulting in vanishing surface area of the star. A generalized Schwarzschild interior solution with conformally flat geometry but with photon emission has been obtained. It is pointed out that the interior conformal coordinate system bears a strong resemblance to the exterior Krushkal coordinates. It is shown that for spherical star the invariant velocity of the fluid particles, falling towards the centre, is proportional to its radius suggesting that the outer envelopes collapse at a faster rate than the core part. It is shown that the interior radiating solution can be matched with generalized Schwarzchild exterior solution.     

J0相干角向偏振涡旋光束的深聚焦

通过矢量德拜理论,研究了J0相干角向偏振涡旋光束深聚焦的性质。推导了在焦点区域的光强分布、光谱相干度和偏振度的表达式。数值模拟结果表明,光强分布、相干度和偏振度不仅依赖于相干长度和数值孔径最大角,而且依赖于拓扑电荷数。这种光束在焦平面还可获得非常小的焦点和焦洞。     

Molecular contrast in optical coherence tomography by use of a pump-probe technique

We describe a novel technique for contrast enhancement in optical coherence tomography (OCT) that makes possible molecular-specific imaging for what is believed to be the first time. A pump-probe technique is employed in which a pulsed pump laser is tuned to ground-state absorption in a molecule of interest. The location of the target molecule population is derived from the resulting transient absorption of OCT sample-arm light acting as probe light. A signal processing technique for three-dimensional localization of the transient absorption signal is described, and preliminary results exhibiting OCT contrast from methylene blue dye in multilayer and scattering phantoms are presented.     

基于电泳法和磁控溅射技术制备金纳米阵列

采用纳米球刻蚀技术中的电泳法设计了3组对照实验,通过控制电压、悬浮液的体积分数和基板正负极性,得到电泳法制备纳米球掩膜板的最佳条件,制备出排布均匀的纳米球单层密堆积结构的掩膜板.采用磁控溅射技术在掩膜板上沉积金薄膜,去除纳米球掩模板,通过扫描电子显微镜观察到周期排列的三角形棱台状金纳米颗粒阵列.测量其吸收光谱,可观察到表面等离子体共振吸收峰.     

大气湍流三维波前探测模式层析算法分析

大气湍流三维波前探测是实现多层共轭自适应光学技术的关键和前提. 对湍流三维波前探测中最常用的模式法层析技术进行理论研究与分析, 提出该算法存在原理性限制, 并基于此对模式法层析技术产生误差的原因展开分析, 最后针对不同类型的模式层析重构误差给出数值仿真实验结果.分析表明, 模式层析重构中使用了Zernike分解基的一部分作为新的分解基进行波面拟合, 从而引入模式混淆和模式耦合两个方面的误差; 部分Zernike分解基不相关是避免模式混淆误差的必要条件, 模式耦合误差则无法避免. 最后结合仿真结果提出大视场探测、小区域重构的方法, 很好地抑制了模式耦合误差. 关键词： 三维波前探测 大气层析 模式法 误差分析     

Study of fiber optic sugar sensor

Over the last two decades, the fiber optic technology has passed through many analytical stages. Some commercially available fiber optic sensors, though in a small way, are being used for automation in mechanical and industrial environments. They are also used for instrumentation and controls. In the present work, an intensity-modulated intrinsic fiber optic sugar sensor is presented. This type of sensor, with slight modification, can be used for on-line determination of the concentration of sugar content in sugarcane juice in sugar industry. In the present set-up, a plastic fiber made of polymethylmethacrylate is used. A portion of the cladding (1 cm, 2 cm, 3 cm) at the mid-point along the length of the fiber is removed. This portion is immersed in sugar solution of known concentration and refractive index. At one end of the fiber an 850 nm source is used and at the other end a power meter is connected. By varying the concentration of sugar solution, the output power is noted. These studies are made due to the change in refractive index of the fluid. The device was found to be very sensitive which is free from EMI and shock hazards, stable and repeatable and they can be remotely interfaced with a computer to give on-line measurements and thus become useful for application in sugar industries.     

Optical absorption and thermoluminescence studies on LiF-Sb2O3-B2O3 glasses doped with Ni ions

20LiF-(30−x)Sb₂O₃-50B₂O₃:xNiO glasses with the value of x (ranging from 0 to 1.0 mol% in steps of 0.2) were prepared. A number of studies, viz. differential scanning calorimetry, optical absorption, magnetic susceptibility and thermoluminescence, on these glasses were carried out as a function of nickel ion concentration. An anomaly has been observed in all the properties of these glasses when NiO concentration is about 0.6 mol%. The results of these studies were analysed in the light of different environments of nickel ions in the glass network.     

Ce3+离子敏化Eu3+∶Cr3+∶Sm3+∶YAG外延层的荧光现象

对Ce3+ ∶Eu3+ ∶Cr3+ ∶Sm3+ ∶YAG处延层中的荧光敏化现象进行了报道和分析 ,在较高浓度的Ce3+ 离子掺杂时 ,外延层在蓝色、绿色波段出现了新的荧光谱线 ,可解释为在Ce3+ 离子敏化作用下 ,Eu3+ 离子产生了由高位激发态能级5Di(i=1,2 ,3)直接到基态能级7Fj(j =0 ,1,2 ,3)的辐射跃迁过程 ,并且这种Ce3+ ∶Eu3+ ∶Cr3+ ∶Sm3+ ∶YAG外延层还是一种新颖的白色单晶荧光材料。