Coherent interaction of picosecond frequency-tunable light pulses with excitons in a semiconductor

An investigation was made of the self-induced transparency effect in the semiconductor's exciton region using ultrashort frequency-tunable light pulses and an ultrafast streak camera.     

Multiphoton parametric processes during interaction of counterpropagating light pulses with sodium vapour

The visible ( 589nm) and IR ( 820nm) radiation has been detected, when two counterpropagating light pulses, nondegenerate in frequency, interacted with sodium vapour. The generated IR radiation was attributed to the fluorescence between 3D and 3P sodium levels, while conical geometry of visible radiation indicated the parametric origin of detected emission.     

交叉传播激光脉冲与等离子体相互作用产生的等离子体密度光栅

理论上研究了两束交叉传播的激光束与等离子体相互作用产生的电子和离子密度调制. 用一维粒子模拟程序(particle-in-cell,PIC)研究了两束激光脉冲产生的干涉场激发的等离子体布拉格光栅. 研究表明等离子体初始密度、脉冲强度和宽度共同影响等离子体布拉格光栅的演化. 光栅的密度峰值可以达到初始等离子体密度的8倍以上,并且可以维持几皮秒的时间. 等离子体布拉格光栅可以囚禁由受激拉曼散射形成的电磁孤子,从而形成准稳态的孤子结构,很大程度上降低了形成电磁孤子所要求的激光脉冲强度. 关键词： 等离子体布拉格光栅 电磁孤子 交叉传播激光束 粒子模拟     

Hydrodynamic interaction between two spheres

We evaluate the hydrodynamic interaction tensors for two spheres of unequal size and for general mixed slip-stick boundary conditions. A method of reflections leads to a series expansion for the diffusion tensors in powers of the inverse distance l^?1 between sphere centers and explicit results are derived through terms of order l^?7. It turns out that the series expansion for the diffusion tensors converges much more rapidly than that for the friction tensors.     

Ultralocalized superluminal light pulses

We consider a sophisticated localized light wave—the so-called focused X wave which possesses a strong exponential localization in its waist region and propagates faster than the speed of light in a vacuum or in a linear medium. We show how this wave—until now considered in the literature as a mathematical object only—could be generated in reality by making use of cylindrical diffraction gratings.     

Movement and amplification of exciton condensed phase pulses and interaction between pulses in semiconductor quantum wells

Formation and movement of an exciton pulse in an inhomogeneous potential are studied. It is shown that the pulse does not blur and the maximum of the exciton density in the pulse remains constant during the exciton lifetime if the pulse is formed from the condensed phase. The path, traversed by the excitons, can be increased by imposing an additional laser pulse on the system. Thereby, such a system can be used for information transmission over the exciton condensed phase.     

Propagation of femtosecond light pulses

Femtosecond transform limited light pulse propagation in vacuum is described in scalar approximation of diffraction theory. Evolution of the spatial and temporal characteristics of the pulse are presented.     

Photorefractive deceleration of light pulses

We theoretically study the effect of light deceleration in photorefractive nonlinear media. This includes consideration of different types of the photorefractive nonlinear response, different wave interaction schemes, and an analysis of the influence of the input parameters, such as the input temporal pulse width and the coupling strength, on the output pulse characteristics: the time delay, the propagation velocity, the amplification factor, and the output width. We show that photorefractive light deceleration has numerous advantages over other known techniques. It works already at low intensities, at room temperature, and within wide spectral ranges and offers a vast variety of handles for manipulating light pulses. An analogy with the light deceleration method based on the quantum effect of electromagnetically induced transparency in ultracold resonant gases is also considered. The text was submitted by the authors in English.     

Search for light neutron-rich isotopes in stopped pion absorption

The results based on the spectroscopy of superheavy hydrogen isotopes (^4?7H), heavy helium isotopes (^6,7He), and heavy lithium isotopes (^7?12Li) produced in stopped pion absorption by light nuclei were analyzed. Search for nuclear states was performed in inclusive and correlation measurements of missing mass spectra. A broad range of excitation energies studied in correlation measurements provided the possibility of search for isobaric analog states and cluster resonances. A comparison with experimental and theoretical results of other authors was conducted.     

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.     

Inelastic interaction of ultrashort pulses of polarized light with an ensemble of isolated quantum dots

A system of equations is formulated describing the evolution of a slowly varying envelope of an arbitrarily polarized ultrashort pulse of electromagnetic radiation in a medium with its resonant properties determined by an ensemble of isolated quantum dots. It is assumed that the concentration of quantum dots is small and that the whole system is equivalent to a gas of resonant four-level atoms. Particular solutions are found that correspond to the propagation of a stationary optical pulse. It is shown by numerical solution of the generalized truncated Maxwell-Bloch equations that steady-state propagation is possible only for circularly polarized light pulses, whereas the pulses of arbitrary polarization either decay and experience the dispersion-related broadening or are converted into circularly polarized solitary waves.     

Hydrodynamic interaction between two rotating tori

The hydrodynamic interactions between two rotating tori is studied. Two kinds of problems are addressed. The interaction between two force free tori is examined, for co and counter rotating cases, which should be relevant in the case of swimming of two toroidal animals and form the basis for interaction of a swarm of such swimmers, apart from the dynamics of a collection of stiff polymer rings. The second problem is the case of two non-translating rotating tori, a possible configuration in toroidal mixers for microfluidic devices. In the former case, analytical expression for translational velocity shows good agreement with the theory in the far field case and show a strong reduction in the velocities in the lubrication limit for the co-rotating case. The velocities are found to monotonically reduce to zero in the case of counter-rotating tori. For the latter case, the expression for velocity field is derived the net force acting on the torus is analytically calculated. The comparison with numerical results is encouraging both in the case of co as well as counter-rotation. The expressions derived for velocities should be useful in estimating pseudo-potentials between such pairs.     

激光与相对论电子束相互作用中阿秒X射线脉冲的产生

本文对激光与相对论电子束相互作用产生的阿秒X射线脉冲进行了研究.阿秒X射线脉冲是由于激光被相对论运动的电子束经过汤姆孙后向散射产生的.讨论了等离子体参数对产生的阿秒X射线的影响.发现其波长随着入射激光的频率的增加或电子束的速度增加而减小.选择合适的参数还可以获得"水窗"波段的X射线.还讨论了相对论电子束的密度与其前沿的密度梯度的大小对所产生X射线的转化效率的影响. 关键词： 阿秒X射线脉冲 汤姆孙后向散射 超强激光 相对论电子束     

Electrostatic interaction between two conducting spheres

In the paper we consider the problem of the electrostatic interaction between two charged conducting spheres with arbitrary electrical charges and radiuses. Using the image charges method we determine exact analytical formulas for the force F and for the potential energy W of the interaction between these two spheres as well as for the potential V of the electromagnetic field in an arbitrary point created by them. Our formulas lead to Coulomb’s law for point charges.We theoretically prove the experimentally shown fact that two spheres with the same type (positive or negative) of charges can also attract each other.     

Driving light pulses with light in two-level media

A two-level medium, described by the Maxwell-Bloch system, is engraved by establishing a standing cavity wave with a linearly polarized electromagnetic field that drives the medium on both ends. A light pulse, polarized along the other direction, then scatters the medium and couples to the cavity standing wave by means of the population inversion density variations. We demonstrate that control of the applied amplitudes of the grating field allows one to stop the light pulse and to make it move backward (eventually to drive it freely). A simplified limit model of the Maxwell-Bloch system with variable boundary driving is obtained as a discrete nonlinear Schr?dinger equation with tunable external potential. It reproduces qualitatively the dynamics of the driven light pulse.     

Effects of interaction between two bubble scatterers

The backscattering of sound from two regularly arranged bubbles is studied theoretically and experimentally. In well-controlled laboratory experiments a bistatic acoustic system is used to interrogate the scatterers, which are placed on a very fine thread at the same distance d from the combined beam axis of the set of transmitting and receiving transducers. The radius of each bubble is 585 microm. The frequency range is 80-140 kHz, and d is varied so that the variable kd spans the range 0.2-21, where k is the acoustic wave number. Scattering calculations are carried out using an exact, closed-form solution derived from the multiple scattering series. Several experiments are performed, and the results are in close agreement with the calculations. It is verified that multiple scattering induces an oscillatory behavior about the exact coherent scattering level, with decreasing amplitude for increasing kd. For interbubble distance 2d approximately lambda/2 the backscattered radiation is maximized, while for 2d相似文献   

Determination of effective interaction between two plasmons

Using the Bohm-Pines hamiltonian the problem of the bound state of two plasmons is investigated following two different decoupling procedures where the energy transfer $\text{Ω = 0}$ or 2ω_pl. The effective interaction g₄ between the two plasmons is found to be repulsive for $\text{Ω = 2ω}{}_{\mathrm{pl}}$ and attractive when $\text{Ω = 0}$. The case of $\text{Ω= 2ω}{}_{\mathrm{pl}}$ is shown to be analogous to the situation under which the critical coupling g_4c is determined.     

组合脉冲的相对相位对谐波谱截止位置的影响

通过数值求解一维含时薛定谔方程,本文研究了组合脉冲与氢原子模型相互作用的高次谐波谱,组合脉冲由基频钛宝石激光和它的二次谐波构成. 研究发现,当两束脉冲之间的相对相位取值不同时,谐波谱的截止位置呈现较大差异. 对此,采用半经典的“三步”模型给出了合理的分析. 本文的数值结果表明,尽管双色谐波谱的结构复杂,截止频率不能用一个简单的公式表示,但通过“三步”模型计算同样能准确预言出截止频率.     

Spectral features of the interaction of femtosecond light pulses of different frequencies near the boundary of a Kerr medium

The interaction of probe ultraviolet (UV) and intense infrared (IR) pump pulses with a duration of 150 fs in a thin 2-mm-long sample of fused silica has been studied theoretically and experimentally. The spectra of UV radiation at the output of the sample have been measured depending on the time delay between the pulses at the sample input. The maximum shifts of the spectrum, attaining up to 0.22 nm for an IR power density of 3 × 10¹¹ W/cm², have been observed under conditions of coincidence of the pulses at the sample input and output, which corresponds to a predominant interaction of the probe radiation with the leading and trailing edges of the pump pulse near the boundary of the medium. The observed dependences are interpreted as a manifestation of the cross-phase modulation due to the Kerr nonlinearity of the medium and the dispersion of the group velocities of the UV and IR pulses. The numerical simulations performed taking into account these effects agree well with the experimental data.