纳米级精度分光路双频干涉度量系统的设计

为完成快速、精确的外观轮廓度量,设计了一种新型纳米级精度分光路双频干涉度量系统。系统由低频差双频激光干涉度量模块和微探头及二维工作台两部分组成。微探针以轻敲式接近样品至几十纳米时,受原子力作用发生偏转,利用双频干涉模块度量其纵向偏转量,并对样品进行梳状式度量得到外观形貌。根据双频激光的实际光源,对原有双频干涉度量理论进行了改进提高。进行了系统组建和实验验证。结果表明:系统具有纳米级精度,可用于超精样品外观轮廓度量。     

Energy levels in doped SiGe quantum well studied by admittance spectroscopy

SiGe/Si quantum wells (QWs) with different Boron doping concentrations were grown by molecular beam epitaxy (MBE) on p-type Si(1 0 0) substrate. The activation energies of the heavily holes in ground states of QWs, which correspond to the energy differences between the heavy hole ground states and Si valence band, were measured by admittance spectroscopy. It is found that the activation energy in a heavily doped QW increases with doping concentration, which can be understood by the band alignment changes due to the doping in the QWs. Also, it is found that the activation energy in a QW with a doping concentration of 2 × 10²⁰ cm⁻³ becomes larger after annealing at a temperature of 685 °C, which is attributed to more Boron atoms activation in the QW by annealing.     

腔内倍频调Q激光器中脉冲光场的时间不稳定性研究

以腔内倍频调Q激光器工作原理为基础,研究了多种形式抽运光分布的情况下倍频光的脉冲形状以及脉冲持续过程中光场分布的时间不稳定性,分析了倍频光光束质量随时间的变化规律.发现腔内倍频调Q激光器输出的倍频光光场分布在脉冲的持续过程中并不稳定,呈持续变化.对高斯型抽运的情况研究发现,减小腔长会使脉冲光场分布的不稳定性减小;而增加...     

Experimental investigation on partially coherent higher-order non-diffractive beams

We experimentally study the generation of a partially coherent non-diffractive beam by focusing a partially coherent vortex beam with an axicon. The investigation results show that when the partially coherent vortex beam is focused by the axicon, the beam is transferred into a partially coherent higher-order non-diffractive beam. In the non-diffractive zone, the transverse intensity distribution of the partially coherent higher-order non-diffractive beam is invariant during propagation. In addition, the range of the non-diffractive zone is related to the coherence of the partially coherent vortex beam. The poorer the coherence of the partially coherent vortex beam, the shorter the range of the non-diffractive zone.     

Evaluation of the dosimetric characteristics of a radiophotoluminescent glass dosimeter for high-energy photon and electron beams in the field of radiotherapy

We aimed to evaluate the suitability of a glass dosimeter (GD) for high-energy photon and electron beams in experimental and clinical use, especially for radiation therapy. We examined the expanded dosimetric characteristics of GDs including dose linearity up to 500 Gy, uniformity among GD lots and for individual GDs, the angular dependence, and energy dependence of 4 therapeutic x-ray qualities. In addition, we measured the dosimetric features (dose linearity, uniformity, angular dependence, and energy dependence) of the GD for electron beams of 10 different electron energy qualities. All measurements with the exception of dose linearity for photon beam were performed in a water phantom. For high-energy photon beams, dose linearity has a linear relationship for a dose ranging from 1 to 500 Gy with the coefficient of determination; R² of 0.998. The uniformity of each GD of dose measurements was within ±0.5% for four GD lots and within ±1.2% for 80 GDs. In terms of the effects of photon beam angle, lower absorbed doses of within 1.0% were observed between 60° and 105° than at 90°. The GD energy dependence of 4 photon beam energy qualities was within ±2.0%. On the other hand, the result of the dose linearity for high-energy electron beams showed well fitted regression line with the coefficient of determination; R² of 0.999 between 6 and 20 MeV. The uniformity of GDs exposed to the nominal electron energies 6, 9, 12, 16, and 20 MeV was ±1.2%. In terms of the angular dependence to electron beams, absorbed doses were within 2.0% between 60° and 105° than at 90°. In evaluation of the energy dependence of the GD at nominal electron energies between 5 and 20 MeV, we obtained responses between 1.1% and 3.5% lower than that for a cobalt-60 beam. Our results show that GDs can be used as a detector for determining doses when a high-energy photon beam is used, and that it also has considerable potential for dose measurement of high-energy electron beam.     

Bi-Sb-Te基热电薄膜温差电池离子束溅射制备与表征

本文采用离子束溅射Bi/Te和Sb/Te二元复合靶,直接制备n型Bi₂Te₃热电薄膜和p型Sb₂Te₃热电薄膜.在退火时间同为1 h的条件下,对所制备的Bi₂Te₃薄膜和Sb₂Te₃薄膜进行不同温度的退火处理,并对其热电性能进行表征.结果表明,在退火温度为150 ℃时,制备的n型Bi₂Te₃关键词： 薄膜温差电池 2Te₃薄膜')" href="#">Sb₂Te₃薄膜 2Te₃薄膜')" href="#">Bi₂Te₃薄膜 离子束溅射     

Propagation characteristics of annular laser beams passing through the reflection Bragg grating with deformation

When high-power annular laser beams produced by the unstable resonator pass through the volume Bragg grating (VBG), absorption of light in the VBG will induce a temperature increment, resulting in changes in surface distortion. Considering that the surface distortion of the grating induces index and period differences, the scalar wave equations for the annular laser beams propagating in the VBG have been solved numerically and iteratively using finite-difference and sparse matrix methods. The variation in intensity distributions, the total power reflection coefficient, and the power in the bucket (PIB) for the annular laser beams passing through the reflection VBG with deformation have been analyzed quantitatively. It can be shown that the surface distortion of the VBG and the beam orders of the annular beams affect evidently the intensity distributions, the power reflection coefficient, and the PIB of the output beam. The peak intensity decreases as the deformation of the VBG increases. The total power reflection efficiency decreases significantly with the increase in deformations of the VBG. The PIB of the output beam decreases as the obscuration ratio β and the deformation of the VBG increase. For the given obscuration ratio β, the influence of deformation of reflection VBG on the PIB of the annular beams is more sensitive with increase in distortion of the VBG and decrease in beam order.     

无铅四方相钙钛矿短周期超晶格压电效应机理研究

超晶格压电行为与内部正离子之间的内在联系尚缺乏相关的研究.本文基于密度泛函理论的第一性原理方法,研究了三种无铅四方相钙钛矿铁电超晶格(BaTiO_3/SrTiO_3,KNbO_3/KTaO_3和BaTiO_3/KNbO_3)中A,B位正离子对整体的极化和压电贡献.通过计算超晶格不同轴向应变条件下原子结构和Born有效电荷,获得了超晶格和各个正离子的极化值和压电系数.结果表明,在轴向压缩应变条件下(-0.15—0 A),无铅超晶格中的正离子位移D(A)和D(B)受到抑制,在拉应变时位移才显著增大,因此极化和压电行为不明显.在轴向拉伸应变作用下(0—0.15 A),无铅超晶格中各原子的极化贡献显著增大,特别是B位原子Ti,Nb和Ta的极化贡献使得总的极化强度也显著提高,并当拉应变达到一定值,超晶格才会出现明显的压电行为.无铅超晶格的极化和压电行为主要由B位正离子贡献.     

刻槽绝缘平行板对电子束的导向效应研究

采用不同材质的刻槽绝缘平行板,包括高纯度石英玻璃、聚四氟乙烯（Teflon）、酚醛树脂（电木）和聚甲醛板（赛钢板）,并在15 pA/mm2 ~14.3 nA/mm2范围内改变入射流强,利用1 500 eV电子束入射上述绝缘平行板,实验研究了上述平行板对电子束的导向行为。实验发现,上述电子束通过上述平行板时存在明显的导向现象,其导向行为与束流流强和绝缘材质无关。据此,可排除绝缘平行板内表面沉积电荷自组织充放电过程中,以绝缘材料的面电阻和体电阻对地泄放的线性形式放电过程。Adopting several grooved parallel plates made by different insulators, such as high-purity fused quartz, Teflon, Bakelite and POM (Polyformaldehyde), and further adjusting the electron beam current in a wide range (tens of pA~tens of nA), the discharging mechanism in the self-organizing charge and discharge processes of electron guiding was investigated and discussed by using 1 500 eV incident electron beam. The present results show that, the electron guiding behaviors are obviously existing when such electron beam is transmitted through the above grooved insulating parallel plates, which are independent on beam current and insulators. Our results suggest that, the possibilities of the accumulated charges on inner-surface of grooved parallel plates linearly discharging through surface and bulk resistances of plates into the ground should be excluded.     

同轴相对论速调管周期永磁聚焦系统的初步研究

为了探索相对论速调管放大器(RKA)的小型化技术,开展了同轴RKA周期永磁聚焦的物理与设计技术研究。周期永磁聚焦系统采用Halbach阵列结构,产生的磁场类型为周期性会切磁场。首先给出该系统的磁场各个分量的表达式,分析该系统磁场分布的特点,并推导得出该系统聚焦强流环形电子束的稳定条件。根据该稳定条件,对Ka波段同轴RKA设计了一个周期永磁聚焦系统,并优化了周期磁场参数,确定了磁场系统设计的最佳周期和幅值。研究结果显示,周期永磁(PPM)聚焦系统在周期长度18 mm和磁场幅值0.33 T的条件下可引导500 kV、6 kA的同轴RKA,得到1 GW的微波输出功率,物理分析确定了周期永磁聚焦系统应用于高功率同轴RKA的技术可能性。