Study of terahertz interferometric imaging using optical techniques

<正>Principles of terahertz(THz) interferometric synthetic aperture imaging with heterodyne and optical techniques are presented.A THz interferometric experiment based on optical up-conversion is set up.The received THz signal is modulated into an optical carrier and transmitted in a fiber.To simulate phase differences between two THz receivers,the output of receiver is divided and a phase shifter is placed before electro-optical modulation(EOM).Interferometric spectra of these modulated optical signals are examined at different phase shifts.Otherwise,carrier suppression and phase error calibration are discussed for THz interferometric synthetic aperture imaging.     

Level Set interface treatment and its application in Euler method

Level Set interface treatment method is introduced into Euler method,which is employed for interface treatment method for multi-materials. Combined with the ghost fluid method,the moving interface is tracked. Fifth-order WENO spatial discretization and third-order TVD Runge-Kutta time discretization methods are used. Shock-wave action on bubble,implosion and velocity field Shock effect bubbles; implosion and velocity field are simulated by means of LS-MMIC3D programmed by C++. Nu-merical results show that t...     

纳米相氟氧化物玻璃陶瓷Tm（0.35）Yb（5）∶FOV的上转换发光

研究了纳米相氟氧化物玻璃陶瓷Tm(0.35)Yb(5)∶FOV在975nm半导体激光激发下的上转换发光。发现了位于363.6,(462.6,477.0),648.7,(699.7,680.7)和(777.6,800.7nm)的几条上转换发光线,它们是Tm3 离子的1D2→3H6,1G4→3H6,1G4→3F4,3F3→3H6和3H4→3H6的荧光跃迁。为了确认它们的上转换机理,还测量了上转换发光强度F随975nm泵浦激光功率P改变的双对数曲线,结果证实了1D2能级的上转换发光部分是五光子上转换发光,而1G4能级和3H4能级的上转换发光则是三光子和双光子上转换发光。     

光纤环中的Shupe效应及其补偿方法研究

本文研究了光纤环的时变温度场,在此基础上对Shupe效应进行了定量分析,并且提出了通过模型修正以减小Shupe效应的补偿方法.     

微光学元件复制技术研究

本文介绍了一种用硅橡胶做模具、光照固化光敏胶的微光学元件复制技术.利用这种方法成功地复制了各种单元尺寸的微光学元件.获得复制精度高、表面粗糙度低、光学性能良好的元件.并可批量生产,降低生产成本.     

Compact and high-power broadband terahertz source based on femtosecond photonic crystal fiber amplifier

We present a review of the development of a compact and high-power broadband terahertz (THz) source optically excited by a femtosecond photonic crystal fiber (PCF) amplifier.The large mode area of the PCF and the stretcher-free configuration make the pump source compact and very efficient.Broadband THz pulses of 150 μW extending from 0.1 to 3.5 THz are generated from a 3-mm-thick GaP crystal through optical rectification of 12-W pump pulses with duration of 66 fs and a repetition rate of 52 MHz.A strong saturation effect is observed,which is attributed to pump pulse absorption;a Z-scan measurement shows that three-photon absorption dominates the nonlinear absorption when the crystal is pumped by femtosecond pulses at 1 040 nm.A further scale-up of the THz source power is expected to find important applications in THz nonlinear optics and nonlinear THz spectroscopy.     

Isospin dependence of nuclear multifragmentation in statistical model

The evolution of nuclear disintegration mechanisms with increasing excitation energy, from compound nucleus to multifragmentation, has been studied by using the Statistical Multifragmentation Model (SMM) within a micro-canonical ensemble. We discuss the observable characteristics as functions of excitation energy in multifragmentation, concentrating on the isospin dependence of the model in its decaying mechanism and break-up fragment configuration by comparing the A₀=200, Z₀=78 and A₀=200, Z₀=100 systems. The calculations indicate that the neutron-rich system (Z₀=78) translates to a fission-like process from evaporation later than the symmetric nucleus at a lower excitation energy, but gets a larger average multiplicity as the excitation energy increases above 1.0 MeV/u.     

顺变柱体型全光纤加速度检波器

介绍了顺变柱体型全光纤加速度检波器的工作原理及结构设计，该检测器包括两个顺变柱体和一个质量块，两顺变柱体上都紧紧地绕着单模光纤，形成了迈克耳孙干涉仪的两个臂，两干涉臂的端面镀有高反铝膜，初步测试结果表明，检波器在共振频率以上有较好的频率响应，输入信号与输出信号吻合得较好。     

Heterodyne direct-detection OOFDM system with low sampling rate

A method of multi-channel receiving for high bit rate heterodyne direct-detection optical orthogonal frequency-division-multiplexing （OOFDM） system is proposed to reduce the sampling rate demand of analog-to-digital converter （ADC）. The sampling rate of ADCs can be reduced to 1/N that of the original signal bandwidth in an N-channel receiving system. Aided by a succeeding digital signal processing （DSP） at the receiver, aliasing free signal can be recovered. A back-to-back experimental result is given for a 4-channel system, based on which, a down conversion process for heterodyne can be reduced. The signal rebuilding algorithm is given and analyzed in its complexity and noise tolerance.     

驻波的能量分析与MATLAB模拟

分析了驻波能量、能量密度、能流密度在传播过程中的转换规律.用Matlab程序实现了驻波波形、能量密度、能流密度的计算机模拟,形象地展现了驻波传播过程中的能量变化,计算机模拟结果与理论分析所得结果一致.最后得到了在振动过程中驻波能量不断地从波节到波腹间相互转移,而从整体看驻波不传播任何能量的结论.