自发产生相干对Y型四能级原子系统探测吸收的影响

在与三个场相互作用的Y型四能级原子系统中,利用密度矩阵方程计算了介质对探测场的吸收,分析了自发产生相干对探测吸收的影响.结果发现:随着自发产生相干的影响,在共振中心处,探测吸收表现出不同的现象.当自发产生相干对探测吸收产生相消干涉时,随着自发产生相干的增强,在共振中心处削弱吸收,出现增益.当自发产生相干对探测吸收产生相长干涉时,随着自发产生相干的增强,在共振中心处出现吸收增强,也即出现电磁诱导吸收(electromagnetically induced absorption,简称EIA),在共振两侧的双电磁感应透明强度(electromagnetically induced transparency,简称EIT)增强,窗口变宽.同时,在能级| 3〉→| 2〉与| 4〉→| 2〉的自发衰减速率比值不变下,当能级|3〉→|2〉与|4〉→|2〉的自发衰减速率减小时,在共振中心处,吸收线宽变窄,共振两侧的透明窗口变宽.     

Measurements of NO2 mixing ratios with topographic target light scattering-differential optical absorption spectroscopy system and comparisons to point monitoring technique

A topographic target light scattering-differential optical absorption spectroscopy(ToTaL-DOAS) system is developed for measuring average concentrations along a known optical path and studying surface-near distributions of atmospheric trace gases.The telescope of the ToTaL-DOAS system points to targets which are located at known distances from the measurement device and illuminated by sunlight.Average concentrations with high spatial resolution can be retrieved by receiving sunlight reflected from the targets.A filed measurement of NO2 concentration is performed with the ToTaL-DOAS system in Shijiazhuang in the autumn of 2011.The measurement data are compared with concentrations measured by the point monitoring technique at the same site.The results show that the ToTaL-DOAS system is sensitive to the variation of NO2 concentrations along the optical path.     

Study on spatial resolution of micromegas as a neutron detector under condition of high neutron flux and γ ray background

In this paper Micromegas has been designed to detect neutrons. The simulation of the spatial reso-lution of Micromegas as neutron detector is carried out by GEANT4 toolkit. The neutron track reconstruction method based on the time coincidence technology is employed in the present work. The influence of the flux of incident 14 MeV neutron and high gamma background on the spatial resolution is carefully studied. Our results show that the spatial resolution of the detector is sensitive to the neutron flux, but insensitive to the intensity of γ background if the neutron track reconstruction method proposed by our group is used. The γ insensitivity makes it possible for us to use the Micromegas detector under condition which has high γ-rays background.     

A prototype of a high rating MRPC

Six-gap resistive plate chamber (MRPC) prototypes with semiconductive glass electrodes (bulk resistivity～1010.cm) were studied for suitability in time-of-flight (TOF) applications at high rates. These studies were performed using a continuous electron beam of 800 MeV at IHEP and an X-ray machine. Time resolutions of about 100 ps and efficiencies larger than 90% were obtained for flux densities up to 28 kHz/cm2.     

Ferroelectric and dielectric properties of SrBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript> thin films grown on Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> film layer

Ferroelectric and dielectric properties of bilayered ferroelectric thin films, SrBi₄Ti₄O₁₅ grown on Bi₄Ti₃O₁₂, were investigated. The thin films were annealed at 700°C under oxygen atmosphere. The bilayered thin films were prepared on a Pt(111)/Ti/SiO₂/Si substrate by a chemical solution deposition method. The dielectric constant and dielectric loss of the bilayered thin films were 645 and 0.09, respectively, at 100 kHz. The value of remnant polarization (2P _r) measured from the ferroelectric thin film capacitors was 60.5 μC/cm² at electric field of 200 kV/cm. The remnant polarization was reduced by 22% of the initial value after 10¹⁰ switching cycles. The results showed that the ferroelectric and dielectric properties of the SrBi₄Ti₄O₁₅ on Bi₄Ti₃O₁₂ ferroelectric thin films were better than those of the SrBi₄Ti₄O₁₅ grown on a Pt-coated Si substrate suggesting that the improved properties may be due to the different nucleation and growth kinetics of SrBi₄Ti₄O₁₅ on the c-axis-oriented Bi₄Ti₃O₁₂ layer or on the Pt-coated Si substrate.     

Deterministic Bidirectional Remote State Preparation of a- and Symmetric Quantum States with a Proper Quantum Channel

We present a new scheme for deterministically realizing the mutual interchange of quantum information between two distant parties via selected quantum states as the shared entangled resource. We first show the symmetric bidirectional remote state preparation (BRSP), where two single-qubit quantum states will be simultaneously exchanged in a deterministic manner provided that each of the users performs single-qubit von Neumann measurements with proper measurement bases as well as appropriate unitary operations, depending essentially on the outcomes of the prior measurements. Then we consider to extend the symmetric protocol to an asymmetric case, in which BRSP of a general single-qubit state and an arbitrary two-qubit state is investigated successfully. The necessary quantum operations and the employed quantum resources are feasible according to the present technology, resulting in that this protocol may be realizable in the realm of current physical experiment.     

Removal of oxygen from silicon by electron beam melting

Small amounts of multicrystalline silicon were melted in an electron beam furnace in different experimental conditions in order to investigate the oxygen evaporation behavior during the electron beam melting (EBM) process. The oxygen content level before and after EBM was determined by secondary ion mass spectroscopy. The oxygen content was reduced from 6.177 to 1.629 ppmw when silicon was melted completely at 15 kW with removal efficiency up to 73.6 %. After that, it decreased continually to <0.0517 ppmw when the refining time exceeded 600 s with a removal efficiency of more than 99.08 %. During the melting process, the evaporation rate of silicon is 1.10 × 10^?5 kg/s. The loss of silicon could be reduced up to 1.7 % during oxygen removal process to a desirable figure, indicating EBM is an effective method to remove oxygen from silicon and decrease the loss of silicon.     

高辐射效率超宽谱脉冲辐射天线的设计与实验

设计了一种采用共面TEM馈电结构的抛物反射面超宽谱脉冲辐射天线,分析了该种馈电结构的阻抗特性与辐射特性。实验表明当馈入电压为3kV、前沿180ps的超宽谱脉冲时,该天线主轴辐射场测试距离与峰值场强之积平均值达到18.3kV,相较于常用的TEM喇叭馈电的超宽带反射面天线,其辐射效率有了显著的提高。     

A diode laser spectrometer at 634nm and absolute frequency measurements using optical frequency comb

This paper reports that two identical external-cavity-diode-laser (ECDL) based spectrometers are constructed at 634 nm referencing on the hyperfine B-X transition R(80)8-4 of ¹²⁷I₂. The lasers are stabilized on the Doppler-free absorption signals using the third-harmonic detection technique. The instability of the stabilized laser is measured to be 2.8×10^-12 (after 1000 s) by counting the beat note between the two lasers. The absolute optical frequency of the transition is, for the first time, determined to be 472851936189.5 kHz by using an optical frequency comb referenced on the microwave caesium atomic clock. The uncertainty of the measurement is less than 4.9 kHz.     

一种新型微结构光纤的设计与数值研究

提出了一种新型双包层结构的微结构光纤(MOF),利用有限元法对其模场面积、损耗及色散系数随波长的变化规律进行了数值模拟与分析,并在相同条件下与传统的双包层MOF作了比较。结果表明,该种光纤不但结构新颖,而且较传统光纤有更优异的色散性能。通过合理优化,设计了几种在500nm波长范围内保持低平色散和较大模场面积的新型双包层MOF。这种光纤结构的提出对以后的理论研究和工艺制备具有一定的参考意义。