矢量效应对超短脉冲光束非傍轴传输的影响

从严格的矢量非傍轴传输方程出发,并通过傅里叶变换及角谱分析的方法,分析了在超短脉冲光束中,矢量效应对其在自由空间中的非傍轴传输的影响。结果表明,矢量效直对脉冲光束的标量傍轴解的修正有着重要的影响,当对脉冲光束进行非傍轴传输处理时,必须考虑它的矢量特性。基于上述分析,得到了支配超短脉冲光束传输的矢量非傍轴方程的一个完整积分解。从这个积分解出发,通过对电场进行泰勒级数展开的方法,得到了一种相对简单的方法,通过这种方法,可以从脉冲光束的已知标量傍轴解来求出矢量非傍轴波动方程的相对精确解。     

傍轴光束在单轴晶体中传输的矢量性质

研究了垂直光轴入射的傍轴光束在单轴晶体中传输的矢量性质.通过角谱的方法得到了寻常光（o光）和非常光（e光）在晶体中传输的严格解，并得到了傍轴近似下的矢量传输模型.利用这一模型，分析得到了垂直光轴偏振的入射光束在晶体中只激发o光，而平行光轴偏振的入射光束在晶体中同时激发e光和二阶小量的o光. 关键词： 傍轴传输 单轴晶体 矢量效应     

宽频带光束非线性热像效应的实验研究

实验研究宽频带脉冲光束通过非线性介质时的非线性热像的形成过程，揭示了光束入射功率和脉冲宽度、介质厚度等因素对热像光强和位置的影响. 结果表明，与单纵模激光束一样，在宽频带脉冲光束情形下，非线性介质上游元件的模糊斑调制也可导致在下游共轭位置形成热像. 热像光强随入射光束功率的增加而增加；若脉冲能量一定，则热像光强随脉冲宽度的增加而减弱；若脉冲峰值功率一定，则热像光强随脉冲宽度的增加而增强. 关键词： 高功率激光 热像 宽带光束 小尺度自聚焦     

强非局域空间三维光孤子短程相互作用

利用强非局域非线性介质中傍轴光束传输的线性模型,根据不共面对称斜入射(1+2)维空间光孤子相互作用的解析解讨论了短程作用的情况.由能量守恒和动量守恒发现,这样的孤子在传输过程中其质心轨迹随着光束之间存在相位差而发生偏转.给出了最佳相位差,即以该相位差入射可以使光束质心偏转达到最大,使得在强非局域介质中通过调节相位差对三维光孤子实现全光控制成为可能.不同的振幅比对质心偏转也有影响.数值模拟了(1+2)维光孤子传输过程中坡印廷矢量(能流密度),分析了光孤子在传输过程中的坡印廷矢量变化,揭开了三维空间光孤子围绕 关键词： 强非局域非线性介质 空间光孤子 短程作用 坡印廷矢量     

强非局域非线性介质中光束传输的Ince-Gauss解

利用强非局域非线性介质中傍轴光束传输的线性模型（Snyder-Mitchell模型）讨论了椭圆坐标系下光束传输过程，通过设立Ince多项式对Gauss函数的调制解得到了强非局域非线性介质中光束稳定传输的Ince-Gauss解.当Ince-Gauss光束的入射功率为临界功率时，光束保持孤子形式传输，否则传输光束的束宽呈现周期性波动，即为呼吸子形式.同时还数值模拟了呼吸子的传输过程.Ince-Gauss光在一定条件下可以连续转换为Hermite-Gauss光或Laguerre-Gauss光，图示展现了几个低阶Ince型光孤子及其转换情况. 关键词： 强非局域非线性介质 Ince-Gauss光 Laguerre-Gauss光 Hermite-Gauss光     

自聚焦克尔类电介质中非傍轴光束调制非稳的研究

将非傍轴效应等效为四阶空间色散、五阶非线性效应和自陡峭效应加以处理.利用线性稳定法研究非傍轴光束在非线性克尔介质中的传播稳定性.理论分析和数值模拟均表明，入射功率p₀和非傍轴参量a决定非傍轴光束调制非稳增益谱呈现出三种不同的分布规律，并给出相应判据以区分三种不同分布. 关键词： 非傍轴光束 调制非稳 增益谱 克尔介质     

非傍轴双曲余弦-高斯脉冲电磁光束远场特性

利用矢量瑞利-索末菲衍射积分公式,推导出了非傍轴部分空间相干部分光谱相干双曲余弦-高斯(ChG)脉冲电磁光束在自由空间传输时交叉谱密度矩阵的远场解析公式,并用来表示脉冲电磁光束的光谱密度(光强)和偏振度。结果表明,对非傍轴远场部分空间相干部分光谱相干ChG脉冲电磁光束,其非傍轴性主要由参数f, f决定,而离心参数、脉冲宽度和时间相干长度影响其非傍轴行为。非傍轴部分空间相干部分光谱相干高斯-谢尔模型脉冲电磁光束的远场传输可作为特例处理。     

有限宽平板波导中的克尔空间孤子及全光器件的设计

利用数值模拟的方法研究了倾斜入射的傍轴光束在有限宽非线性平板波导内的传输规律.研究发现，当不同波长相同束宽的光束各以临界功率倾斜入射波导时，如果倾斜角、入射点都一样，它们将沿大致相同的周期性的Z字形路径传输；如果光束功率进一步增大，相邻反射点之间的间距随传输距离有逐渐变大的趋势，Z字形路径不再有严格的周期性；当功率相当大时，光束将沿波导z方向传输，不再在波导的两个边界之间来回反射.利用倾斜入射光束在波导内的传输路径随功率而变的特点，设计了一个功率开关和一个光时分解复用器. 关键词： 空间光孤子 有限宽非线性平板波导 全光器件     

基于ABCD矩阵的Z-扫描理论

基于光学系统对傍轴激光束的传输与变换技术—ABCD定理,以非线性相移为研究对象,采用表征高斯光束特征的q参量在光束无像散近似假设下,分析了Z-扫描测量方法的理论基础,得到了表达简单的解析理论公式.在非线性相移｜ΔΦ0｜<π rad时,所得模拟结果可以很好地与已知理论结果相吻合.对CS2和纳米碳管乙醇溶液的非线性测量及数据的拟合,证明了用此结论进行数据分析的简洁性和优越性.     

双曲余弦高斯光束在强非局域介质中的传输

从描述强非局域介质中光束传输的非线性薛定谔方程出发,研究了(2+1)维双曲余弦高斯光束在强非局域介质中的传输性质及其相互作用,给出了双曲余弦高斯光束在强非局域非线性介质中传输的解析表达式和二阶矩束宽的解析表达式,同时对两束双曲余弦高斯光束之间的相互作用进行了解析和数值分析。结果表明单光束入射强非局域介质时,存在一个临界功率,当入射功率等于临界功率时,光束在传输过程中的二阶矩束宽可以保持不变;当入射功率不等于临界功率时,光束的二阶矩束宽呈周期性变化。两束双曲余弦高斯光束共同传输时会相互吸引,并且横向强度分布变的较为复杂,给出了两束光传输时相互作用后的强度分布和轴上光强演化等结果。     

Effect of the nonlinear compression of ultrashort microwave pulses in the process of the amplification by quasistationary electron beams

An effect of the nonlinear compression of ultrashort microwave pulses has been observed in the process of the amplification of quasistationary electron beams. The Cherenkov mechanism of the interaction of a rectangular electron beam with a decelerated wave in a waveguide partially filled with an insulator is used. The experiment has been conducted on a setup consisting of two synchronized RADAN high-current accelerators. The first accelerator supplied a generator of 37-GHz superradiance pulses with a duration of about 300 ps. The second accelerator with a beam current of up to 1.2 kA and an electron energy of about 300 keV was used in an amplifying section. The theoretical analysis shows that the amplification of the electromagnetic pulses (at least by a factor of 4 in the power) is accompanied by a strong decrease in their duration (down to 100 ps).     

Self-induced transparency,compression, and stopping of electromagnetic pulses interacting with beams of unexcited classical oscillators

The self-induced transparency effects that emerge when short (on the relaxation time scale) light pulses propagate in a two-level noninverted medium are well known in optics. The interaction of microwave pulses with an initially rectilinear electron beam under cyclotron resonance conditions can serve as a classical analog of the described effects. In this case, at a certain intensity of the input signal, the cyclotron absorption is replaced by self-induced transparency when the input pulse propagates almost without any change of its profile, forming a soliton whose amplitude and duration are rigidly related to its velocity. In a certain domain of parameters, this process is accompanied by significant two- or threefold compression of the initial pulse, which is of practical interest for the generation of multigigawatt picosecond microwave pulses. Since the soliton velocity lies between the unperturbed group velocity of the radiation and the translational velocity of the particles, another nontrivial effect in the case of interaction with a counterpropagating electron beam is the possibility of a significant deceleration or full stopping of the electromagnetic pulse.     

Beam spot size evolution of Gaussian femtosecond pulses after angular dispersion

Beam spot size evolution of spatially Gaussian femtosecond laser pulses after angular dispersion is analyzed and verified with experiments. A general analytical expression for beam spot size at arbitrary propagation distances is obtained, which indicates that beam spot size evolution after angular dispersion is determined by the direct interaction of spectral lateral walk-off by angular dispersion and the intrinsic divergence of the Gaussian beam. This work reveals insights into the propagation of Gaussian femtosecond laser pulses and beams after angular dispersion and may be important for the generation and application of femtosecond laser pulses.     

Scattering light by short acoustic pulses in a crystalline collinear cell and coherent processing of ultra-high frequency radio-wave electronic pulses

We present the study of collinear light scattering by relatively short acoustic pulses in birefringent crystals providing that both the acoustic attenuation and spreading the acoustic beam are allowed for. The exact and closed analytical model for the phenomenon described is developed. The peculiarities of collinear acousto-optical interaction in the cells made of lithium niobate single crystal are considered for the traveling-wave regime. The feasibility of applying such an effect to perform a coherent optical processing of ultra-high frequency (UHF) radio-wave electronic pulses is analyzed and the corresponding opto-electronic algorithm is elaborated. The results of preliminary experiments, exhibiting an opportunity for the data processing in anti-radar system, are presented.     

Coherent interaction of picosecond pulses in a fluorescent medium and the timing of pulse trains for two-wavelength excite and probe measurements

Coherent interaction between two cw, picosecond pulse trains of the same wavelength absorbed by a fluorescent material and the effect on the emission has been studied. As the path difference between the two beams is varied, the infra-red emission from colour centres in KCl: Na or KCl: Li fluctuates in phase with the transmitted intensity of the weaker of the two beams. The effect may be applied to the accurate relative timing of cw pulse trains of different wavelengths for use in two-wavelength, excite and probe measurements. A small fraction of the pump pulse train is superimposed on the probe beam and passes along precisely the same optical path. Coherent interaction between the two pulse trains at the pump frequency causes modulation of the transmitted probe beam intensity when pump and probe pulses are accurately synchronised.     

相对传播的双脉冲激光与薄膜靶作用产生的强单色谐波

研究了相对传播的双脉冲激光与薄膜靶的作用,观察到很强的谐波产生.其物理图像是:圆偏振高对比度强激光脉冲作用于薄膜靶,由光压推动产生的高密度等离子体靶向前运动,同时由于电荷分离场的作用,使得离子束和电子束在纵向上都有好的聚束,从而产生以相对论速度向前运动的等离子体镜;反向入射一个探测光到已被加速的等离子体镜上,由多普勒频移产生强的单色N次谐波,探测光脉冲被"压缩"至原来的1/N.还讨论了激光和等离子体参数对等离子体镜的运动和谐波级次的影响,以及相对论运动等离子体镜的稳定性对谐波的影响.     

Spatial beam profiles of femtosecond X-ray pulses generated by laser Compton scattering from a low-emittance electron beam

Polarization-dependent spatial beam profiles of femtosecond X-ray pulses generated by a laser Compton scheme were measured. The X-ray pulses were generated by the interaction at an angle of 90° between 100-fs laser light and a 3-ps, 3π-mm mrad electron beam. The polarization of the laser light was linear in two different directions, either parallel or perpendicular to the electron beam axis. The measured profiles showed good agreement with theoretical results. Received: 5 July 2002 / Revised version: 17 October 2002 / Published online: 5 February 2003 RID="*" ID="*"Corresponding author. Fax: +81-424/684477, E-mail: msf_yorozu@shi.co.jp     

Observation of the second harmonic in Thomson scattering from relativistic electrons

A free relativistic electron in an electromagnetic field is a pure case of a light-matter interaction. In the laboratory environment, this interaction can be realized by colliding laser pulses with electron beams produced from particle accelerators. The process of single photon absorption and reemission by the electron, so-called linear Thomson scattering, results in radiation that is Doppler shifted into the x-ray and gamma-ray regions. At elevated laser intensity, nonlinear effects should come into play when the transverse motion of the electrons induced by the laser beam is relativistic. In the present experiment, we achieved this condition and characterized the second harmonic of Thomson x-ray scattering using the counterpropagation of a 60 MeV electron beam and a subterawatt CO2 laser beam.     

Laser seeding of the storage-ring microbunching instability for high-power coherent terahertz radiation

We report the first observation of laser seeding of the storage-ring microbunching instability. Above a threshold bunch current, the interaction of the beam and its radiation results in a coherent instability, observed as a series of stochastic bursts of coherent synchrotron radiation (CSR) at terahertz frequencies initiated by fluctuations in the beam density. We have observed that this effect can be seeded by imprinting an initial density modulation on the beam by means of laser "slicing." In such a situation, most of the bursts of CSR become synchronous with the pulses of the modulating laser and their average intensity scales exponentially with the current per bunch. We present detailed experimental observations of the seeding effect and a model of the phenomenon. This seeding mechanism also creates potential applications as a high-power source of CSR at terahertz frequencies.     

Dissociation dynamics of H+2 in intense laser fields: investigation of photofragments from single vibrational levels

We present a photodissociation experiment on H+2 with ultrashort laser pulses ( >/=130 fs) at peak intensities of 相似文献