基于双通预脉冲清洁及腔内频谱滤波的高对比度飞秒激光再生放大器

为了提高再生放大器输出激光脉冲的对比度,需要同时提高激光脉冲纳秒尺度的对比度和皮秒尺度的对比度。利用普克尔盒对主脉冲和预脉冲时间滤波的方法,设计了普克尔盒的双通预脉冲清洁装置,通过该装置使再生放大器输出激光纳秒尺度的预脉冲对比度提高了5个数量级;利用频谱整形方法,通过在放大器腔内适当位置插入频谱整形滤波片使得主脉冲前400 ps处的放大自发辐射对比度提高了1个数量级。最终,在双通预脉冲清洁与腔内频谱滤波共同作用下,再生放大器输出激光纳秒尺度的预脉冲对比度从4.3×10^-4提高到了6.6×10^-10,放大自发辐射对比度(主脉冲前400 ps)从5.0×10^-8提高到了5.0×10^-9。     

氨气高精度激光光谱检测装置的设计及实现

氨气排放会对环境以及人体健康造成危害,因此对环境中氨气浓度的高精度监测显得尤为重要。本文基于具有高灵敏度、高响应速度等优点的离轴积分腔输出光谱技术(OA-ICOS)对氨气高精度检测装置进行设计。使用基长30 cm装有反射率为99.99%的高反镜的光学谐振腔作为气体吸收池,实现了近3 000 m的光程,将中心波长为1 528 nm的分布反馈式激光器(DFB)调谐至6 548.611 cm^-1和6 548.798 cm^-1附近,在常温18.6 kPa的气压下对1×10^-5～5×10^-5范围内NH₃进行了检测。测量结果表明NH₃浓度与信号幅值的线性拟合度R²可达0.999 79。使用Allan方差对实验数据进行分析得到13 s后系统的平均检测极限为9.8×10^-9,在103 s时系统的最低检测极限可达7×10^-9(S/N～1)。实验结果表明,该检测装置具有良好的稳定性与高灵敏度,满足对氨气高精度检...     

一种铷原子钟超高信噪比物理系统的研究

在卫星导航、深空探测等尖端技术应用的需求牵引下,谱灯抽运铷原子钟的性能有了很大提升,其短期频率稳定度已达到小系数10^-13τ^-1/2水平.为能进一步提高铷钟稳定度并探索铷钟性能指标极限,本文在前期对物理系统(Φ40微波腔)结构的重新设计及实验验证的基础上,通过对物理系统的光学系统全面优化设计,改善了光谱灯及抽运光的性能,最终使物理系统信噪比获得了明显提升.测试及分析评估结果表明,新设计的物理系统的散粒噪声对铷钟稳定度的贡献为4.2×10^-14τ^-1/2,本文的研究结果为今后铷钟短稳实现5×10^-14τ^-1/2、长稳突破1×10^-15进入～10^-16奠定了基础.     

低损宽频高双折射太赫兹光子带隙光纤

设计了一种低损耗、宽频段、高双折射太赫兹光子带隙光纤,呈三角晶格排列的亚波长空气孔包层实现了带隙的局域作用.利用全矢量有限元法对光纤的双折射及损耗特性进行了理论分析.结果表明,在大约0.3 THz的宽频范围内,类矩形纤芯太赫兹光子带隙光纤的损耗小于0.009 cm^-1,相双折射在10^-3数量级,群双折射可达10^-2数量级. 关键词： 太赫兹 太赫兹波导 光子晶体光纤 双折射     

聚合物P3HT在不同退火温度下的空穴传输特性

运用交流阻抗方法系统研究了单空穴注入型器件ITO/PEDOT/P3HT/Ag（P3HT：poly（3-hexylthiophene））在多种退火温度下的电容-频率变化关系,推算出样品中相应条件下的空穴迁移率,发现退火温度对空穴迁移率有明显影响,未经过退火的样品空穴迁移率为10^-4cm²/Vs数量级,迁移率数值基本不随电场强度的改变而变化,退火后样品的空穴迁移率有明显提高,约为10^-3cm²/Vs数量级,此时,空穴迁移率 关键词： 空穴迁移率 聚合物 电容-频率特性     

基于光纤的光学频率传递研究

随着光钟研究的发展, 光钟的稳定度和不确定度均达到10^-18量级. 通过光纤可以实现光钟频率信号的高精度传输, 有望用于未来“秒”定义的复现. 演示了百公里级实验室光纤上的光学频率传递. 对于在实验室70 km光纤盘上实现的光频传递, 光纤相位噪声抑制在1-250 Hz傅里叶频率范围内均接近于光纤延时极限, 对应传输稳定度(Allan偏差)为秒级稳定度1.2×10^-15, 10000 s稳定度为1.4×10^-18. 实验室100 km光纤的光频传递秒级稳定度也达到了5×10^-15. 提出了光纤噪声用户端补偿的方案, 可以简化星形传递网络中心站的复杂度. 在25 km光纤上演示了该传递方案, 实现的传输稳定度接近传统前置补偿传递方案.     

在地球引力场中进行广义相对论第四类实验的可能性

本文用广义相对论计算了引力场对干涉仪的影响。结果表明,如果象通常那样把物理长度定义为固有长度,那么当把干涉仪转动90℃时条纹移动为2.2×10^-10(其中取干涉仪臂长1m,光波波长为1μm)。 关键词：     

基于单一量子级联激光器的大气多组分气体（CO、N2O、H2O）同时测量方法

近红外波段的气体吸收强度低,不利于痕量气体的测量。利用分子在中红外波段的基频吸收特性,使用单个新型室温连续输出量子级联激光器（CW-QCL）结合波长调制光谱技术（WMS）和长程光学吸收池,建立了一套高灵敏度和高精度的大气多组分温室气体同时检测的激光光谱系统。该系统的输出波数范围为2202.8～2205.6 cm^-1,覆盖了CO、N₂O和H₂O的中心吸收谱线。实验测试结果表明：在1 s的时间分辨率下,CO、N₂O和H₂O的测量精度分别为1.83×10^-8,1.86×10^-9,1.19×10^-4;当满足最佳积分时间（100 s）时,系统的最低检测限可以达到1.8×10^-9（CO）,0.16×10^-9（N₂O）,1.5×10^-5（H₂O）。通过长时间测量和分析可知,所提系统部件简单,使用方便,满足大气多组分气体...     

类摩天轮型多孔纤芯超高双折射率太赫兹光子晶体光纤特性

提出一种以新型聚合物Topas作为基底材料的类摩天轮型多孔芯光子晶体光纤。利用时域有限差分法对光纤的双折射率、损耗及色散等特性进行数值模拟。结果表明：该光纤在3～6 THz的工作频段内可提供10^-1数量级的双折射率,在4 THz处达到0.1085的超高双折射率、10^-1 dB/cm的总损耗、10^-16 dB/cm的极低限制损耗和2.4×10^-14 dB/cm的低弯曲损耗;该光纤在3～5.5 THz频率范围内拥有近零色散值,为±0.11 THz^-2·cm^-1。该光纤的良好特性对太赫兹光器件以及偏振传感等领域的发展具有促进作用。     

锐钛矿金红石的高温原位X射线衍射研究

对TiO₂粉末进行了空气和真空条件下从室温到1200℃的加热原位X射线衍射实验, 得到了空气和真空条件下微米级锐钛矿颗粒转变为金红石的起始温度分别为850℃ 和855℃; 分别修正了空气条件下锐钛矿在(27–850℃)范围和金红石在(900–1200℃) 范围内的晶胞参数和真空条件下锐钛矿在(27–850℃)范围和金红石在(950–1200℃) 范围的晶胞参数, 从而得到了晶胞参数随温度变化的关系, 得到了锐钛矿和金红石在空气中和真空中的热膨胀系数, 并总结了热膨胀系数随温度变化的规律. 室温下锐钛矿在空气条件下的热膨胀系数为 α_a=4.55063×10^-6/℃, α_c=7.7543×10^-6/℃, β=16.85836×10^-6/℃; 真空下为 α_a=4.69429×10^-6/℃, α_c=9.02850×10^-6/℃, β=18.69688×10^-6/℃. 室温下, 金红石在空气条件下的热膨胀系数为 α_a=6.81243×10^-6/℃, α_c=8.71644×10^-6/℃, β=22.22178×10^-6/℃; 真空条件下为 α_a=6.05834×10^-6/℃, α_c= 8.39280×10^-6/℃, β=20.52362×10^-6/℃. 关键词： 2')" href="#">TiO₂ 原位X射线衍射 相转变 热膨胀     

Two-body scattering without angular-momentum decomposition: Fully off-shell T-matrices

Two-body scattering is studied by solving the Lippmann-Schwinger equation in momentum space without angular-momentum decomposition for a local short-range interaction plus Coulomb. The screening and renormalization approach is employed to treat the Coulomb interaction. Benchmark calculations are performed by comparing our procedure with a configuration space calculation, using the standard partial-wave decomposition, for ¹²C - ¹⁰Be elastic scattering. The fully off-shell T -matrices are also calculated for the final goal of studying the three-body scattering by solving Faddeev/AGS equations.     

Numerical solutions of the orbital equations for diatomic molecules

A basis of Hermite splines is used in conjunction with the collocation method to solve the orbital equations for diatomic molecules. Accurate solutions of the Hartree-Fock equations are obtained using iterative methods over most regions of space, while solving the equations by Gaussian elimination near the nuclear centres. In order to improve the speed and accuracy of our iterative scheme, a new self-adjoint form of the Hartree-Fock equation is derived. Using this new equation, our iterative subroutines solve the Hartree-Fock equations to one part in 10⁶. The Gaussian elimination routines are accurate to better than one part in 10⁸.     

Transient response of infrared photoconductors: The roles of contacts and space charge

The transient response of an extrinsic photoconductor, with two implanted ohmic contacts, has been calculated by solving the full continuity equation using a variable finite difference technique. For a step function in photon flux under constant voltage bias, transient times ranging from 10^–4 to 10^–2 s have been determined for 20 to 200 m thick detectors under the low background fluxes typical of infrared astronomy. The transient response consists of a fast and a slow component, with their relative magnitudes dependent on the ratio of diffusion and drift lengths to the device length. The characteristic time for the fast component is determined, as expected, by the carrier lifetime, but a slower transient response is also present which is controlled by out-diffusion and sweep-out and the establishment of a counteracting electric field barrier. The effects of material and operating parameters have been investigated, and an analytical model is presented for estimating transient response times for any extrinsic photoconductor. Contact-limited transient response will be most limiting for operation of thin device structures under very low photon backgrounds.     

Variational aspects of Faddeev calculations

We examine differences between³H binding energies obtained by solving the Faddeev equations using standard partial-wave expansion procedures and results from solving the Schrödinger equation by means of the coupled-rearrangement-channel variational method. Variational bounds generated from Faddeev solutions for several contemporary, realistic potential models are presented as a function of the number of partial waves retained in the potential expansion. We demonstrate that the Faddeev wave function yields an optimal variational bound for the partial-wave truncated potential from which it is generated, but it does not yield optimal bounds for the full Hamiltonian or when the potential is partial-wave truncated at a different level. Finally, qualitative differences between³H solutions for static models such as the AV14 and RSC potentials and for momentum-dependent models such as the Nijmegen soft-core and Paris potentials are explored, and comparison is made with solutions for the RSC/TM two-body-force plus three-body-force model.     

关于铁磁链方程的反散射解法的严格证明和验证

本文对于通常证明中引入的造成困难的因子λ^-1,证明不仅应当略去,而且在略去后,同样可以得到与Takhtajan方程等价的结果,只在λ=0处有预料到的修正。同时,给出了反散射解法的解满足铁磁链方程的普遍验证。 关键词：     

入射电子能量对低密度聚乙烯深层充电特性的影响

高能带电粒子与航天器介质材料相互作用引起的深层带电现象, 一直是威胁航天器安全运行的重要因素之一. 考虑入射电子在介质中的电荷沉积、能量沉积分布以及介质中的非线性暗电导和辐射诱导电导, 建立了介质深层充电的单极性电荷输运物理模型. 通过求解电荷连续性方程和泊松方程, 可以得出不同能量 (0.1–0.5 MeV) 电子辐射下, 低密度聚乙烯 (厚度为1 mm) 介质中的电荷输运特性. 计算结果表明, 不同能量的电子辐射下, 介质充电达到平衡时, 最大电场随入射能量的增加而减小; 同一能量辐射下, 最大电场随束流密度的增大而增加. 入射电子能量较低时 (≤ 0.3 MeV) , 最大电场随束流密度的变化趋势基本相同. 具体表现为: 当束流密度大于3× 10^-9 A/m²时, 最大场强超过击穿阈值2×10⁷ V/m, 发生静电放电 (ESD) 的可能性较大. 随着入射电子能量的增加, 发生静电放电 (ESD) 的临界束流密度增大, 在能量为0.4 MeV时, 临界束流密度为6×10^-8 A/m². 当能量大于等于0.5 MeV时, 在束流密度为10^-9–10^-6 A/m²的范围内, 均不会发生静电放电 (ESD) . 该物理模型对于深入研究深层充放电效应、评估航天器在空间环境下 深层带电程度及防护设计具有重要的意义. 关键词： 高能电子辐射 低密度聚乙烯(LDPE) 介质深层充电 电导特性     

单频导纳谱法测量锗硅量子阱的能带偏移

提出了用单频导纳谱法测量储硅单量子阶的能带偏移，与常规的多频导纳谱相比，它只需测一个频率的导纳谱就能得到更精确的实验结果。用该方法对Ｓｉ／Ｇｅ_０．３３Ｓｉ_０．６７／Ｓｉ单量子阱进行测试，得到激活能为Ｅ_a＝０．２０ｅＶ。为了计算出能带偏移值，必须能准确确定具有单量子阱结构样品中的费密能级位置，由于在单量子阱结构中费密能级的位置与阱材料、垒材料的掺杂浓度、阱的高度（即能带偏移）及温度等几个因素均有关。为此，本文通过解泊松方程，计算出结合本文样品 关键词：     

Leakage current and capacitance characteristics of Si/SiO2/Si single-barrier varactor

We investigate, both experimentally and theoretically, current and capacitance (I–V/C–V) characteristics and the device performance of Si/SiO₂/Si single-barrier varactor diodes (SBVs). Two diodes were fabricated with different SiO₂ layer thicknesses using the state-of-the-art wafer bonding technique. The devices have very low leakage currents (about 5×10^-2 and 1.8×10^-2 mA/mm²) and intrinsic capacitance levels of typically 1.5 and 50 nF/mm² for diodes with 5-nm and 20-nm oxide layers, respectively. With the present device physical parameters (25-mm² device area, 760-μm modulation layer thickness and ≈10¹⁵-cm^-3 doping level), the estimated cut-off frequency is about 5×10⁷ Hz. With the physical parameters of the present existing III–V triplers, the cut-off frequency of our Si-based SBV can be as high as 0.5 THz. Received: 9 February 2001 / Accepted: 9 February 2001 / Published online: 23 March 2001     

Numerical spectral analysis of a grid: Application to strain measurements

We present a nondestructive and noncontact extensometry technique, which has been developed in order to study the behavior of different materials such as polycarbonate, araldite, urethane, etc. A spectral analysis of a crossed grating marked on the surface of a specimen and recorded by a charge coupled device camera is presented. The procedure is based on the use of a bidimensional fast Fourier transform algorithm coupled with an interpolation process. It leads to the accurate determination of frequencies. Numerical simulations have been made to evaluate the strain sensitivity; it depends on both the initial phase and the number of cycles characterizing the grid. Theoretically, the strain sensitivity can reach 10^-5 in best cases, but practically it is notbetter than 10^-4. Several applications on different materials are presented: polyurethane, paper and cloth.     

Computing multi-valued physical observables for the high frequency limit of symmetric hyperbolic systems

We develop a level set method for the computation of multi-valued physical observables (density, velocity, energy, etc.) for the high frequency limit of symmetric hyperbolic systems in any number of space dimensions. We take two approaches to derive the method.The first one starts with a weakly coupled system of an eikonal equation for phase S and a transport equation for density ρ:

The main idea is to evolve the density near the n-dimensional bi-characteristic manifold of the eikonal (Hamiltonian–Jacobi) equation, which is identified as the common zeros of n level set functions in phase space . These level set functions are generated from solving the Liouville equation with initial data chosen to embed the phase gradient. Simultaneously, we track a new quantity f = ρ(t,x,k)|det(_k)| by solving again the Liouville equation near the obtained zero level set = 0 but with initial density as initial data. The multi-valued density and higher moments are thus resolved by integrating f along the bi-characteristic manifold in the phase directions.The second one uses the high frequency limit of symmetric hyperbolic systems derived by the Wigner transform. This gives rise to Liouville equations in the phase space with measure-valued solution in its initial data. Due to the linearity of the Liouville equation we can decompose the density distribution into products of function, each of which solves the Liouville equation with L^∞ initial data on any bounded domain. It yields higher order moments such as energy and energy flux.The main advantages of these new approaches, in contrast to the standard kinetic equation approach using the Liouville equation with a Dirac measure initial data, include: (1) the Liouville equations are solved with L^∞ initial data, and a singular integral involving the Dirac-δ function is evaluated only in the post-processing step, thus avoiding oscillations and excessive numerical smearing; (2) a local level set method can be utilized to significantly reduce the computation in the phase space. These methods can be used to compute all physical observables for multi-dimensional problems.Our method applies to the wave fields corresponding to simple eigenvalues of the dispersion matrix. One such example is the wave equation, which will be studied numerically in this paper.