超冷原子中的拉曼增益光栅

为提高光栅的衍射效率,提出了基于主动拉曼效应的超冷原子光栅系统。理论研究表明：通过拉曼增益的空间周期性调节,可有效地将沿垂直光栅方向传播的弱探测光衍射到一级方向,同时零级衍射光将被放大。当系统中引进微波场的原子相干效应时,可以进一步提高光栅的一级衍射效率。在一定的条件下,拉曼增益光栅的一级衍射效率可高于电磁诱导相位光栅的一级衍射效率。该系统可作为高效光开关用于全光网络。     

Coherently induced grating in refractive index enhanced medium

We demonstrate a scheme for coherently induced grating based on a mixture of two three-level atomic species interacting with two standing-wave fields. As a result of interaction between the absorptive and amplified Raman resonances, the refractive index of the medium can be enhanced and modulated periodically. Then a sinusoidal grating, which can diffract the probe field into high-order directions, is coherently formed in the medium. The proposed scheme is theoretically investigated in a mixture of atomic isotopes of rubidium. The results show that the diffraction efficiency depends strongly on the two two-photon detunings of the two Raman transitions and the intensities of the two driving standing-wave fields.The proposed electromagnetically induced grating scheme may be applied to the all-optical switching and beam splitting in optical networking and communication.     

高阶色散对高双折射光纤增益谱的影响

根据参量放大和拉曼效应共同作用下的耦合波方程,在考虑高阶色散情况下,当输入泵浦波偏振方向同双折射轴成45时,通过引入拉曼增益的洛伦兹模型,研究了高双折射光纤中,参量放大和拉曼效应共同作用下的增益谱随相关参量的变化关系。结果表明:高双折射光纤中,在不同色散区,不同的输入参量（输入功率、群速度失配等）条件下,参量放大和拉曼效应共同作用下的增益谱受到高阶色散的影响,增益谱的结构、强度和谱宽产生了变化, 高阶色散对增益谱的影响不可忽略;可以利用增益谱在大群速度失配区域远离中心频率偏移的性质,提取T频率脉冲。     

Temperature dependent direct-bandgap light emission and optical gain of Ge

Band structure, electron distribution, direct-bandgap light emission, and optical gain of tensile strained, n-doped Ge at different temperatures were calculated. We found that the heating effects not only increase the electron occupancy rate in the Γ valley of Ge by thermal excitation, but also reduce the energy difference between its Γ valley and L valley. However,the light emission enhancement of Ge induced by the heating effects is weakened with increasing tensile strain and n-doping concentration. This phenomenon could be explained by that Ge is more similar to a direct bandgap material under tensile strain and n-doping. The heating effects also increase the optical gain of tensile strained, n-doped Ge at low temperature, but decrease it at high temperature. At high temperature, the hole and electron distributions become more flat, which prevent obtaining higher optical gain. Meanwhile, the heating effects also increase the free-carrier absorption. Therefore, to obtain a higher net maximum gain, the tensile strained, n-doped Ge films on Si should balance the gain increased by the heating effects and the optical loss induced by the free-carrier absorption.     

Application of two-dimensional dynamic gain grating for generation of coherent radiation from spatially extended active media

Lasers with light-induced two-dimensional distributed feedback are investigated, in which a two-dimensional grating of the gain of the active medium, induced by several pump laser beams, is used to ensure the coupling of four partial wave flows propagating in mutually orthogonal directions. The starting conditions and nonlinear dynamics of lasers with a new kind of a two-dimensionally distributed feedback are analyzed within the semiclassical approximation. Self-similarity conditions are found, ensuring the scaling of the laser parameters under the conditions of maintenance of steady-state lasing regime upon an increase in the active region size, which is accompanied by an increase in the integrated output power. The effect of diffusion of nonequilibrium carriers on the lasing process and threshold conditions is analyzed.     

正交光栅干涉仪对二维分立点物体成像

本文将正交光栅干涉仪的条纹箱分离,获得两个方向上的条纹箱.对于由N个分立点组成的物体,从两个条纹箱可以得到由N~2个点组成的像.其中N个点是物的格实像点,N(N—1)个是交叉项点.将光栅干涉仪绕其对称轴转过一角度,得到第二个像.与第一个像相比,N(N—1)个交叉项点的空间位置发生了变化,而N个真实像点未变.因此,将这两个像相乘,即能消除交叉项点而获得真实像点.利用这一方法,给出了实验结果.     

波荡器位相误差对自由电子激光

 对波荡器位相误差对自由电子激光小信号增益的影响进行了分析讨论。对低增益情况解析地给出了波荡器位相误差引起的增益降低因子。结果表明：与自发辐射类似增益的降低与位相误差的方差成简单的指数关系，位相误差的线性变化部分引起最大增益的位移，还表明波荡器位相误差存在时Madey定理仍然成立。对高增益情况也给出了波荡器位相误差引起的增益降低因子。     

Gain of harmonic generation in high gain free electron laser

In a planar undulator employed free electron laser (FEL), each harmonic radiation starts from linear amplification and ends with nonlinear harmonic interactions of the lower nonlinear harmonics and the fundamental radiation. In this paper, we investigate the harmonic generation based on the dispersion relation driven from the coupled Maxwell-Vlasov equations, taking into account the effects due to energy spread, emittance, betatron oscillation of electron beam as well as diffraction guiding of the radiation field. A 3D universal scaling function for gain of the linear harmonic generation and a 1D universal scaling function for gain of the nonlinear harmonic generation are presented, which promise rapid computation in FEL design and optimization. The analytical approaches have been validated by 3D simulation results in large range.     

Graphene-tuned threshold gain to achieve optical pulling force on microparticle

We investigate optical force on a graphene-coated gain microparticle by adopting the Maxwell's stress tensor method.It is found that there exists a threshold gain in obtaining the Fano-profile optical force which indicates the reversal of optical pushing and pulling force. And giant pushing/pulling force can be achieved if the gain value of the material is in the proximity of the threshold gain. Our results show that the threshold gain is more sensitive to the relaxation time than to the Fermi energy of the graphene. We further study the optical force on larger microparticle to demonstrate the pulling force occurring at octupole resonance with small gain value and then it will appear at quadrupole resonance by increasing gain value. Our work provides an in-depth insight into the interaction between light and gain material and gives the additional degree of freedom to optical manipulation of microparticle.     

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     

基于包层旋转折变型光纤光栅的动态增益均衡器

提出并利用高频CO₂激光脉冲在普通单模通信光纤上写出了包层旋转折变型长周期光纤光栅(R-LPFG). 在分析R-LPFG波导结构和双折射特性的基础上，对光栅周期数和折变旋转度分别为50和7.2°/周期的R-LPFG进行了实验研究.结果表明，这种类型的光栅可极大地降低其谐振波长对横向负荷不同作用方向所表现出的方向相关性，并且其谐振峰幅度横向负荷灵敏度在任意方向下均高达0.37dB/(g·mm^-1) ，是普通LPFG横向负荷灵敏度的9倍左右.利用R-LPFG的温度线性响应特性和独特的横向负荷特性，设计并实验研究了一种动态增益均衡器，用其平坦掺铒光纤放大器增益谱，在C波段32nm范围内，其平坦度小于±0.5dB，可满足实际环境对通信系统的平坦应用要求. 关键词： 光纤通信技术 长周期光纤光栅 动态增益均衡 旋转折变     

Near diffraction limit output and gain saturation of soft X-ray laser

By using of travelling wave amplification, we have got a soft x-ray laser with near diffraction limit output and gain saturation in the experiment of four series coupling targets with reflector.     

Doppler展宽的封闭原子系统中无反转增益的相位控制

研究了在具有自发辐射诱导相干性的Doppler展宽的封闭Λ型三能级系统中探测场和驱动场之间的相对位相对探测场无反转增益的控制作用. 研究结果表明: 1) 不管探测场和驱动场是同向传播还是反向传播, 驱动场是失谐还是共振,无反转增益总是随相对位相的改变而作周期性变化,周期为2π. 2) 驱动场共振时,无反转增益极大值随Doppler展宽值的增大而单调减小,且反向传播时比同向传播时减小的速度更快;驱动场失谐时,无反转增益的极大值随Doppler展宽值的增大不再单调地减小或增大. 在以上两种情况下,均可以通过调 关键词： 自发辐射诱导相干 相位控制 Doppler展宽 无反转增益     

Absolute time-resolved x-ray laser gain measurement

We present the first direct measurement of the time evolution of the gain of a soft x-ray laser amplifier. The measurement is based on the injection of a seed pulse, obtained by high-order harmonic generation, into an x-ray laser medium. Strong amplification occurs when the seed pulse is synchronized with the gain period. By precisely varying the delay between the x-ray laser plasma creation and the seed pulse injection, the actual temporal evolution of the soft x-ray amplifier gain is obtained with a subpicosecond resolution.     

Near diffraction limit output and gain saturation of soft X-ray laser

Abstract: By using of travelling wave amplification, we have got a soft x-ray laser with near diffraction limit output and gain saturation in the experiment of four series coupling targets with reflector.     

考虑钕玻璃放大器增益特性的光谱色散匀滑系统性能研究

采用数值方法研究了钕玻璃放大器的增益特性对高功率激光系统中光谱色散匀滑单元性能的影响.分析结果表明,入射光中心波长与放大器增益曲线中心波长不一致时,焦斑强度分布会受到一定的影响,且该影响随放大倍数增大趋于明显,而两个波长一致时,强度分布变化较小.靶面焦斑整体的辐照均匀性则主要取决于经过相位调制后的激光束的带宽,放大器的增益特性对其空间功率谱及均匀性无明显的影响.所得结论为光谱色散匀滑单元在激光系统中的实际应用提供了重要的理论参考.     

三代微光像增强器亮度增益测量装置

 微光像增强器是微光夜视仪的核心器件,它是微光夜视整机性能和价格的决定因素。微光像增强器是在微弱的光线下工作的 ,因此必然是光能放大器。亮度增益是评价微光像增强器光电性能的一个重要参数,它直接影响了微光整机的性能,因此,对像增强器的亮度增益测试技术的研究具有重要意义。文中介绍了三代微光像增强器的亮度增益测量原理和装置,并对测量结果进行了不确定度评定。     

Influences of finite gain bandwidth on pulse propagation in parabolic fiber amplifiers with distributed gain profiles

The evolutions of the pulses propagating in decreasing and increasing gain distributed fiber amplifiers with finite gain bandwidths are investigated by simulations with the nonlinear Schr¨odinger equation. The results show that the parabolic pulse propagations in both the decreasing and the increasing gain amplifiers are restricted by the finite gain bandwidth. For a given input pulse, by choosing a small initial gain coefficient and gain variation rate, the whole gain for the pulse amplification limited by the gain bandwidth may be higher, which is helpful for the enhancement of the output linearly chirped pulse energy. Compared to the decreasing gain distributed fiber amplifier, the increasing gain distributed amplifier may be more conducive to suppress the pulse spectral broadening and increase the critical amplifier length for achieving a larger output linearly chirped pulse energy.     

Influences of finite gain bandwidth on pulse propagating in parabolic fiber amplifiers with distributed gain profiles

The evolutions of the pulses propagating in decreasing and increasing gain distributed fiber amplifiers with finite gain bandwidths are investigated by simulating with the nonlinear Schrödinger equation. The results show that the parabolic pulse propagations in both the decreasing and the increasing gain amplifiers are restricted by the finite gain bandwidth. For a given input pulse, by choosing small initial gain coefficient and gain variation rate, the whole gain for the pulse amplification limited by the gain bandwidth may be higher, which is helpful to the enhancement of the output linearly chirped pulse energy. Compared to the decreasing gain distributed fiber amplifier, the increasing gain distributed amplifier may be more conducive to suppress the pulse spectral broadening and increase the critical amplifier length for achieving a larger output linearly chirped pulse energy.     

各向同性光纤中拉曼增益对光脉冲自陡峭的影响

运用数学解析法导出了关于拉曼增益与自陡峭综合效应的光脉冲传输方程,在此基础上引入洛伦兹模型将拉曼增益整合到非线性系数中来研究光脉冲中拉曼增益对自陡峭效应的作用,重点分析了高斯脉冲在各向同性光纤中传播时,拉曼增益对其自陡峭效应具体影响方式,结果表明拉曼增益会减弱自陡峭中后沿偏移程度,减小脉冲展宽,但不会影响其峰值大小.