Compton散射对椭圆偏振激光调制不稳定性的影响

应用相对论理论和多光子非线性Compton散射模型,对等离子体中多光子非线性Compton散射对椭圆偏振光调制不稳定性的影响进行了研究,给出了调制不稳定性的时间增长率修正方程,并进行了数值模拟.结果表明,与散射前相比,Compton散射光越强,引起调制不稳定性的最大时间增长率增量越大.在激光等离子体临界面附近处,散射引起的调制不稳定性的最大时间增长率增量加速了激光场的坍塌.     

Compton散射对未磁化等离子体调制不稳定性的影响

为了研究Compton散射对未磁化等离子体调制不稳定性的影响,采用多光子非线性Compton散射模型,对Compton散射下的未磁化等离子体调制不稳定性进行了理论分析和实验验证,取得了散射对调制不稳定性的时间增长率、非线性色散和控制影响的重要数据,提出了将入射光和Compton散射光作为形成调制不稳定性的新机制。结果表明,Compton散射使未磁化等离子体的自调制不稳定性的最大时间增长率和激光自聚焦较散射前减小,等离子体截面附近处调制不稳定性的时间增长率较散射前增大。     

Compton散射对磁化等离子体调制不稳定性的影响

基于多光子非线性Compton散射模型,研究了多光子非线性Compton散射对激光在磁化等离子体中调制不稳定性的影响.将入射光和多光子非线性Compton散射光作为形成调制不稳定性的新机制,对非线性色散方程和控制方程进行了修正,给出了由入射光和多光子非线性Compton散射光形成的耦合左旋椭圆偏振光调制不稳定性的时间增...     

高功率亚皮秒激光脉冲在气体中的空间—时间不稳定性

研究和演示了亚皮秒高强度激光在其穿过大气密度的空气时形成的散焦介质－等离子体中的空间－时间不稳定性。出现不稳定性的原因是非线性响应与时间的依赖关系。     

极高能量密度激光等离子体中参量不稳定性的控制、超热电子的产生及其应用

极高能量密度激光等离子体中参量不稳定性的控制对非线性物理和惯性约束核聚变;高效台式Ｘ光源及其相关应用等诸多领域均具有极为重要的意义．超短超强激光技术的迅猛发展使我们已有可能利用此类激光的超宽频率带宽所导致的超短相干时间及频率调制能力对极高能量密度激光等离子体中的参量不稳定性进行控制．我们将分别讨论激光等离子体冕区中绝对和对流参量不稳定性的控制原理并指出超短超强激光装置在激光等离子体参量不稳定性控制中的可能应用．此外,我们还将讨论激光等离子体中超热电子的产生机制及其在先进台式Ｘ光显微成像技术（包括…     

非线性光纤传输的若干理论问题(之三) Ⅲ非线性单模光纤中的调制不稳定性理论

本文对非线性单模光纤中的调制不稳定性进行了详细研究,给出了调制不稳定性产生的条件与最大调制增长率等公式,得到了调制不稳定性既可在异常色散区也可在正常色散区产生的结论,确定了维持调制增长对光纤长度选取要求的范围.     

Compton散射下磁化等离子体光子晶体光子带隙特性

为了研究多光子非线性Compton散射对横向磁光效应磁化等离子体光子晶体光子带隙特性的影响,采用多光子非线性Compton散射模型和时域有限差分法进行了理论分析和实验验证,取得了关于晶体色散和调制不稳定性、光子带宽变化的重要数据,并提出了将入射光和Compton散射光作为磁化等离子体光子晶体色散的新机制.结果表明,Compton散射使等离子体色散增强,耦合电磁波通带变窄、阻带变宽,有效地降低了电磁波传输中的交叉相位调制的不稳定性,频率低于等离子体频率的电磁波在等离子体中的传播几率减小.     

高阶非线性单模光纤中调制不稳定性的产生和增长

基于赵阳等(1989)的工作,本文归一化地给出了高阶非线性下单模光纤中调制不稳定性的产生条件和频率范围;得到了最大调制增长率的存在对光纤色散的要求。对数值例子的讨论,得出了一些新的对实际应用调制不稳定性十分有用的结果。     

Compton散射对等离子体MI基态增益谱的影响

应用多光子非线性Compton散射模型和非线性薛定谔方程,研究了多光子非线性Compton散射对等离子体中调制不稳定性基态增益谱的影响,提出了将入射光和Compton散射光作为产生调制不稳定性的新机制,给出了微扰的功率增益表达式,并进行了数值模拟。结果表明,入射光和Compton散射光共同决定了调制不稳定性的基态增益,Compton散射使扰动信号的功率和频率增大,从而使增益谱对应的频率范围和增益峰值增大。     

激光薄膜损伤中等离子体冲击波特征

在不同位置和激光辐照能量的条件下,采用传声器采集并提取了等离子体冲击波的压强值及其起始时间信息,分析了等离子体冲击波在空气中的传播规律,拟合得到了冲击波声压值与激光辐照能量的关系函数。结果表明,激光等离子体冲击波以球面波形式在空气中进行传播,其声压值与激光辐照能量呈非线性的正相关关系。     

Self-focusing and guiding of short laser pulses in ionizing gasesand plasmas

Several features of intense, short-pulse (≲1 ps) laser propagation in gases undergoing ionization and in plasmas are reviewed, discussed, and analyzed. The wave equations for laser pulse propagation in a gas undergoing ionization and in a plasma are derived. The source-dependent expansion method is discussed, which is a general method for solving the paraxial wave equation with nonlinear source terms. In gases, the propagation of high-power (near the critical power) laser pulses is considered including the effects of diffraction, nonlinear self-focusing, ionization, and plasma generation. Self-guided solutions and the stability of these solutions are discussed. In plasmas, optical guiding by relativistic effects, ponderomotive effects, and preformed density channels is considered. The self consistent plasma response is discussed, including plasma wave effects and instabilities such as self-modulation. Recent experiments on the guiding of laser pulses in gases and in plasmas are briefly summarized     

The Linear and Self-Consistent Nonlinear Theory of the Electron Cyclotron Maser Instability

In this paper the linear and nonlinear theory of the electron cyclotron maser instability is considered. The configuration used to study the maser instability consists of relativistic electrons gyrating about and drifting along a uniform magnetic field within a parallel plate waveguide. Relativistic effects associated with the gyrating electrons are responsible for excitation of the transverse electric mode in the waveguide. Linear theory shows that the growth rate maximizes when the axial beam velocity coincides with the axial wave group velocity of the excited electromagnetic wave. This allows us to perform the nonlinear analysis in a frame where both the axial wave number and axial beam velocity vanish. We have found that the maser instability exists only if the perpendicular beam energy exceeds a threshold value. Our analysis also describes the temporal nonlinear evolution of the field amplitude and frequency of a single excited wave. The nonlinear wave dynamics are self-consistently determined from the nonlinear particle orbits through the force and wave equations. The nonlinear analysis shows that there are two possible mechanisms for the saturation of the unstable wave: 1) depletion of the available free energy associated with the rotating particles and 2) phase trapping of the gyrating electrons in the wave. The initial beam parameters determine which of the two mechanisms is responsible for saturation. Competition between the two saturation mechanisms leads to a peaking in the energy conversion efficiency as a function of beam energy. Numerical results of the nonlinear formalism show that energy conversion efficiencies from the particles to the wave can be as high as 60 percent in the beam frame. Furthermore, by appropriately contouring the external magnetic field, among other things, efficiencies as high as 70 percent can be realized.     

Modeling of the frequency modulation response of semiconductordiode lasers

The modulation response of GaAlAs semiconductor diode lasers has been studied theoretically, with emphasis on wavelength modulation or frequency chirp. The laser model used is a nonlinear rate equation model that incorporates the wave equation for the lateral waveguide modes of the laser. Lateral diffusion of carriers in the active layer of the laser is taken into account via a one-dimensional diffusion equation. A small-signal analysis of the model has been performed to obtain the modulation response. The calculated amplitude and phase of the wavelength modulation relative to the power modulation are in good agreement with experiments. It is found that carrier diffusion has only a moderate influence on the modulation response     

飞秒等离子体间非线性作用对超高频电磁波影响的研究

主要研究了飞秒等离子间相互的非线性作用对超高频电磁波——太赫兹波产生的影响。国内外许多研究机构已经证实,在太赫兹波产生的过程中,等离子体间的相互非线性作用会对太赫兹波产生影响。笔者结合理论分析设计并搭建一种了双束等离子体重合产生太赫兹波的测试系统,研究发现等离子体间相互非线性作用时,会产生三阶非线性光学效应,等离子体的折射率和相位发生变化形成非均匀场导致了太赫兹波辐射能量的降低,并在实验测量研究中发现随着等离子体波长双束等离子波长的增加,等离子体密度增加,导致太赫兹波的辐射能量的降低现象更加明显,另外,等离子体功率越大,太赫兹波吸收越大。同时,研究发现等离子体周围惰性气体分子质量影响太赫兹降低程度,气体分子质量决定着飞秒激光聚焦空气电离出的等离子体所形成的电场强度,分子质量越高,所形成的电场强度越强,双束等离子体重合时对太赫兹波降低的辐值越大。这些为研究等离子体间非线性作用对太赫兹波的影响提供了更加全面的理论支撑,有助于推动太赫兹波技术在军事及民用领域的快速发展。     

The physics of the nonlinear optics of plasmas at relativisticintensities for short-pulse lasers

The nonlinear optics of plasmas at relativistic intensities are analyzed using only the physically intuitive processes of longitudinal bunching of laser energy, transverse focusing of laser energy, and photon acceleration, together with the assumption of conservation of photons, i.e., the classical action. All that is required are the well-known formula for the phase and group velocity of light in plasma, and the effects of the ponderomotive force on the dielectric function. This formalism is useful when the dielectric function of the plasma is almost constant in the frame of the light wave. This is the case for Raman forward scattering (RFS), envelope self-modulation (SM), relativistic self-focusing (SF), and relativistic self-phase modulation (SPM). In the past, the growth rates for RFS and SPM have been derived in terms of wave-wave interactions. Here we rederive all of the aforementioned processes in terms of longitudinal bunching, transverse focusing, and photon acceleration. As a result, the physical mechanisms behind each are made clear and the relationship between RFS and envelope SM is made explicitly clear. This allows a single differential equation to be obtained which couples RFS and SM, so that the relative importance between each process can now be predicted for given experimental conditions     

多光子非线性Compton散射下的调制不稳定性对波分复用系统的影响

运用小信号分析法,研究了多光子非线性Compton散射下的调制不稳定性(MI)对波分复用系统的影响,结果表明:计及散射光的调制不稳定性,不仅会使波分复用系统的信噪比(SNR)更快地下降,从而导致信号强度更快地减弱,而且还会对噪声有更大的放大作用;这种调制不稳定性对波分复用系统中各信道的影响是不同的,它对短波段的作用强于长波段,也会使各信道的信噪比产生更大的偏差,将使长波段较短波段有更大的信噪比,信噪比的降低将随着长度的增加有较快的积累.     

升余弦变迹布拉格光纤光栅中的调制不稳定性

利用相干耦合非线性薛定谔方程,研究了激光脉冲在升余弦变迹布拉格光纤光栅中传输时,在反常色散区和正常色散区所产生的调制不稳定性。结果表明在反常色散区和正常色散区都能产生调制不稳定性;在反常色散区,当输入功率达到一定数值时,产生明显的规律性增益谱;在正常色散区,在产生调制不稳定性功率区域,调制不稳定性存在并从给定值一直持续到无穷;在反常色散区和正常色散区,增益谱都受到升余弦变迹函数的制约。     

产生太赫兹辐射源的Nd:YAG双波长准连续激光器

产生太赫兹波辐射的方法可分为电子学和光子学两大类.在光子学领域,非线性光学差频方法是获取高功率、低成本、便携式、室温运转太赫兹波的主要方法之一.实验研究了激光二极管(LD)端面抽运Nd:YAG1319 nm/1338 nm双波长准连续线偏振运转激光器,理论计算了输出双波长在非线性晶体DAST(4-N,N-dimethylamino-4'-N-'methyl-stilbazolium tosylate)中差频产生太赫兹辐射的平均功率.在重复频率50 kHz时,双波长激光平均输出功率达到2.22 W,斜率效率12.72%,线偏振度0.983,脉冲宽度71.91 ns.M2因子仅为1.165,不稳定性小于0.487%.根据非线性差频理论,计算出可在1 mm厚DAST晶体中获得4.71 mw的3.23 THz高相干性太赫兹波辐射.这两条非常接近的谱线为进一步通过非线性光学差频方法获得高相干性太赫兹波提供了理论基础.     

The modulation instability laser. II. Theory

For pt.I see ibid., vol.25, no.9, p.2036-44 (1989). A general analysis of the modulation instability laser (MIL) in a nonlinear dispersive cavity is presented. The theory of the feedback-induced modulational instability is derived. By introducing the pump depletion within one circulation of the pump pulse, the steady-state MIL oscillation can be predicted. The ripple frequency is equal to the modulation instability frequency