脉冲激光场选择性光电离同位素原子

对三个脉冲激光场与两种四能级同位素原子选择性相互作用的动力学过程进行了研究。由旋转波近似下的含时Ｓｃｈｒ?ｄｉｎｇｅｒ方程出发，利用Ｓｙｌｖｅｓｔｅｒ定理分别对于近共振和非共振两种激发过程的动力学方程求解，导出了激发和电离几率的解析表达式。研究结果揭示了窄带强激光激发原子的过程中的相干振荡特性。在近共振激发时，导出了粒子布居在激发态上反转的条件，并由此提供了选择性激发和电离过程中所采用的脉冲激光源之基本参数的选择依据。 关键词：     

四能级双V型原子系统中考虑自发辐射相干的无粒子数反转激光

提出了一个由两个弱探测场和两个强耦合场驱动的四能级双V型原子系统, 研究发现在四波混频共振条件下, 两探测场均可被放大而无须粒子数反转. 值得注意的是, 由于所选择的激发态为超精细结构的两个近能级, 这里必须考虑自发辐射相干效应的影响. 与不考虑自发辐射相干相比, 同样参数条件下探测场的增益得到大幅度提高.而且, 探测场增益对相位非常敏感, 即增益-吸收线型受相位周期性调制, 同时也受两个偶极矩之间夹角θ制约. 此外还分析了相干抽运场 (强耦合场)的失谐对增益谱线产生的影响. 关键词： 无粒子数反转激光 四波混频 自发辐射相干     

GeSe_2中强各向异性偏振相关的非线性光学响应

二硒化锗(GeSe_2)作为一种层状IV-VI族半导体,具有面内各向异性结构及宽能带间隙,表现出了独特的光、电及热学性能.本文利用偏振拉曼光谱和线性吸收谱分别对GeSe_2纳米片的晶轴取向和能带特性进行表征,并以此为依据采用微区I扫描系统研究了GeSe_2在共振能带附近的光学非线性吸收机制.结果表明,GeSe_2中非线性吸收机制为饱和吸收与激发态吸收的叠加,且对入射光偏振与波长均有强烈的依赖.近共振激发(450 nm)条件下,激发态吸收对偏振的依赖程度比较大,随着入射光偏振的不同,非线性调制深度可由4.6%变化至9.9%;而非共振激发(400 nm)时,该调制深度仅由7.0%变化至9.7%.同时,相比于饱和吸收,激发态吸收的偏振依赖程度受远离共振激发波长的影响而变化更大.     

一种单稳随机共振系统信噪比增益的数值研究

采用四阶Runge-Kutta数值求解方法, 发现一种单稳随机共振系统信噪比增益的随机共振现象, 并且在一定的条件下系统信噪比增益大于1.通过调节单稳随机共振系统参数可以改变信噪比增益.本文结果拓展了这类单稳的已有研究范围, 在信号检测与处理以及通信领域有着潜在的应用价值. 关键词： 单稳随机共振 信噪比增益 数值分析 非线性     

射频驱动下电磁诱导透明窗口的分裂和增益的出现

在Λ型三能级系统的基础上引入两个共振射频场, 通过详细讨论系统的探测吸收特性随两个射频场Rabi频率取不同值时的变化规律, 得出电磁诱导透明(EIT)的分裂规律以及EIT上出现增益现象的产生条件.研究结果表明: 两个射频场对系统所起的控制作用不同, 控制基态精细结构能级之间跃迁的射频场对EIT的分裂起作用, 而控制激发态精细结构能级之间跃迁的射频场不会导致EIT的分裂; 而且, 只有当控制基态精细结构能级之间跃迁的射频场的Rabi频率大于控制激发态精细结构能级之间跃迁的射频场的Rabi频率时, 才能产生EIT与增益相叠加的新特性. 关键词： 射频场 电磁诱导透明 增益 精细结构能级     

高离化态Hg和U离子的双电子复合过程的理论研究

在相对论多组态Dirac-Fock理论基础上，利用近期发展的计算双电子复合截面的程序，系统研究了高离化态类氦到类硼Hg和U离子的KLL双电子复合过程. 讨论了Breit效应和量子电动力学(QED)效应对Hg离子共振双激发态能级的贡献，得到了双激发态的共振能、总线宽和相应的双电子复合共振强度，所得结果与其他理论和实验结果都符合得很好. 在此基础上进一步研究了高离化态U离子的KLL双电子复合过程，并与已有的实验和理论结果作了比较.     

高离化态Hg和U离子的双电子复合过程的理论研究

在相对论多组态Dirac-Fock理论基础上,利用近期发展的计算双电子复合截面的程序,系统研究了高离化态类氦到类硼Hg和U离子的KLL双电子复合过程. 讨论了Breit效应和量子电动力学(QED)效应对Hg离子共振双激发态能级的贡献,得到了双激发态的共振能、总线宽和相应的双电子复合共振强度,所得结果与其他理论和实验结果都符合得很好. 在此基础上进一步研究了高离化态U离子的KLL双电子复合过程,并与已有的实验和理论结果作了比较. 关键词： 双电子复合 MCDF     

具有导向磁场的线偏振Wiggler自由电子激光器

本文用单粒子模型,计算了在线偏振Wiggler场上叠加一个均匀轴向磁场,对自由电子相干辐射增益的影响。结果表明,在近共振辐射波长上得到了增益增强,但轴向磁场过强,会引起增益下降。     

Fe~(24+)离子双电子复合以及和H_2 碰撞的共振转移与激发X射线发射过程的研究

以准相对论Hartree-Fock理论为基础,对Fe~(24+)离子KLn(n=L,M,N,O,P)共振激发态可能辐射衰变通道的双电子复合过程的共振强度进行了系统的理论计算研究,计算了KLL共振激发态谱项能级电偶极允许跃迁的共振强度和截面,在此基础上,根据已有H_2分子的实验Compton轮廓,进一步计算了能量在300—800 MeV范围内,抛射体Fe~(24+)离子俘获H_2分子靶电子的KLn(n=L,M,N,O,P)共振电荷转移与激发X射线发射截面,计算结果与最新实验值或者其他理论计算结果做了对比分析,研究表明,对于Fe~(24+)离子KLn(n=L,M,N,O,P)的双激发态,Kα辐射衰变通道对双电子复合过程的共振强度贡献最大,是起主导性作用的重要通道,Kα辐射衰变X射线的波长范围λ为1.850—1.880A,而非Kα辐射衰变的波长范围λ为1.460—1.601 A,两者共振X射线的波长位置并不重叠。     

H_2~+分子与共振相关的阈下谐波的取向效应

通过数值模拟的方法研究了H_2~+阈下谐波的取向效应.数值模拟过程中,主要关注波长为760nm的阈下谐波,通过逐次减去激发态贡献的方法,研究共振相关谐波不同取向角下的变化规律.结果表明:阈下平行、垂直谐波展示的复杂取向依赖与共振效应密切相关,该现象主要由与基态共振的各激发态的轴对称性导致.另外,用包含跃迁偶极子的简单模型对取向效应进行了概括描述,并以H_2~+第一激发态为演化初始态进行了验证.本文结果可为阈下谐波取向效应的实验研究提供参考.     

Electrically tunable slow and fast lights in a quantum-dot semiconductor optical amplifier near 1.55 microm

We have demonstrated both slow light in the absorption regime and fast light in the gain regime of a 1.55 microm quantum-dot semiconductor optical amplifier at room temperature. The theory with coherent population oscillations and four-wave mixing effects agrees well with the experimental results. We have observed a larger phase delay at the excited state than that at the ground state transition, likely due to the higher gain and smaller saturation power of the excited state.     

Probe gain with population inversion in a four-level atomic system with vacuum-induced coherence

For a four-level atomic system with a doublet of closely spaced levels, we find that, owing to the coherence that results from the vacuum of the radiation field, population trapping at excited levels and probe gain with population inversion can be achieved with weak incoherent pumping. This gain is different from both the conventional lasing gain and gain without inversion in that there exists population inversion on probe transitions but the inversion is achieved by the vacuum-induced coherence.     

激发态之间的电离与复合过程对类氖锗19.6nm X射线激光增益系数的影响

考察了激发态之间的电离与复合过程对等离子体状态的影响,并对其原因进行了细致的分析,分别考察了对1.0ns,100ps和5ps激光驱动的类氖锗19.6nm Ｘ射线激光增益系数的影响.研究表明,对于5ps激光驱动的瞬态机理X射线激光来讲,因增益区处在高密度区,所以,激发态之间的电离与复合过程对X射线激光将不可以忽略.对于1.0ns和100ps激光驱动的亚稳态机理X射线激光来讲,在电子密度小于等于5×10²⁰cm^－3的区域,忽略激发态之间的电离与复合使增益的时间半高全 关键词： X射线激光 矩阵分块法 类氖锗 双电子激发态     

Study of high-power Ka-band second-harmonic gyroklystron amplifier

The self-consistent nonlinear theory of two-cavity high-harmonic gyroklystron amplifier has been developed. The efficiency and gain of a second-harmonic gyroklystron were calculated numerically. The results obtained were used to choose the optimal parameters of the experimental second-harmonic tube. The experimental study was carried out to test high-harmonic amplifier concept. Two-cavity 35 GHz second harmonic gyroklystron with the TE₀₂₁ cavity mode has been designed and tested in pulse operation. Output power of about 260 kW with efficiency 18% and 17 dB gain have been produced at 72 kV beam voltage and 20 A beam current. Bandwidth of about 0.1% has been observed. The restriction of the output power, efficiency, and gain was caused by spurious oscillations excited in the second cavity in the TE₀₁₁ mode at the fundamental cyclotron frequency     

Effect of diffraction on the measurement of gain in optically pumped materials

Maxwell's equations are solved for the propagation of light in an inhomogeneously excited material. For a particular form of the inhomogeneity, a closed form solution is found which shows that the optical gain measured by optical pumping experiments will be less than the “intrinsic” gain which would be observed in a homogeneously excited material.     

Experimental studies of an unstable confocal resonator alexandrite laser

The effects of excited converging wave in an unstable confocal resonator onthe properties of an alexandrite laser are investigated experimentally.The results show thatexciting the converging wave inside the resonator is an effective method to reduce the diver-gence of the laser beam for low gain laser medium.     

掺Er及Yb-Er共掺Al2O3光波导放大器的理论与实验研究

抽运波长为0.98μm时,考虑合作上转换、交叉弛豫、激发态吸收等上转换机理给出了掺Er及Yb-Er共掺系统的速率方程,并利用二维波导的有限元理论及包含正反向放大的自发辐射的场传输方程,建立了一套分析光波导放大器增益特性的综合理论模型。得到掺Er及Yb-Er共掺Al2O3光波导放大器增益与波导长度、抽运功率、掺杂浓度等多个参量的关系,绘制出具有实用性的优化设计曲线。将该理论模型应用于实际制作的Yb-Er共掺Al2O3光波导放大器,结果与实验数据相符。     

Complementary electric-LC resonator antenna for WLAN applications

In this paper, a metamaterial antenna based on complementary electric-LC (CELC) resonator is proposed. The antenna consists of slot-loaded ELC on the ground plane as the main antennas radiating element and excited by a microstrip line. The CELC resonator is characterized by single-negative magnetic moment excited by coupling between the microstrip transmission line and slot-loaded CELC. The peak realized gain and efficiency of 2.63 dB and 86 % are obtained, respectively, at resonance frequency. Simulation and measurement results are presented to validate the design. The antenna is suitable for WLAN applications (2.39–2.48 GHz).     

Investigation of gain recovery for InAs/GaAs quantum dot semiconductor optical amplifiers by rate equation simulation

The gain recoveries in quantum dot semiconductor optical amplifiers (QD SOAs) are numerically studied by rate equation simulation. Similar to the optical pump-probe experiment, the injection of double 150 fs optical pulses is used to simulate the gain recovery of a weak continuous signal under different injection levels, inhomogeneous broadenings, detuning wavelengths, and pulse signal energies for the QD SOAs. The obtained gain recoveries are then fitted by a response function with multiple exponential terms to determine the response times. The gain recovery can be described by three exponential terms with the time constants, which can be explained as carrier relaxation from the excited state to the ground state, carrier captured by the excited state from the wetting layer, and the supply of the wetting layer carriers. The fitted lifetimes decrease with the increase of the injection currents under gain unsaturation, slightly decrease with the decrease of inhomogeneous broadening of QDs, and increase with the increase of detuning wavelength between continuous signal and pulse signal and the increase of the pulse energy.