Electron acceleration by a tightly focused laser beam

State-of-the-art petawatt laser beams may be focused down to few-micron spot sizes and can produce violent electron acceleration as a result of the extremely intense and asymmetric fields. Classical fifth-order calculations in the diffraction angle show that electrons, injected sideways into the tightly focused laser beam, get captured and gain energy in the GeV regime. We point out the most favorable points of injection away from the focus, along with an efficient means of extracting the energetic electron with a static magnetic field.     

Electron acceleration in a tightly focused laser beam

Electron acceleration in a tightly focused ultra-intensity linear polarized laser beam is investigated numerically. It has been found that the acceleration is strong phase dependent and is periodic to the variety of the initial laser field phase. When optimal initial parameters are chosen, the electron can be accelerated effectively. The accelerated electrons are emitted in pulses of which the full width is less than the half period of the laser field.     

紧聚焦的飞秒激光脉冲在真空中对电子的加速

研究了紧聚焦的圆偏振飞秒相对论高斯激光脉冲与电子的相互作用，提出了一种激光加速电子的新机制.利用束腰小、强度大的激光脉冲上升沿加速电子，束腰大、强度小的脉冲下降沿减速电子，当光脉冲和电子分离时，电子获得了能量增益.研究发现，初始静止的电子与强度高于10¹⁹Wμm^{2/cm2的光脉冲作用以后，可以获得MeV量级的能量.初始位于焦点附近的电子被加速的效果较好，而远离焦点的电子几乎不能获得能量增益. 关键词： 电子加速 能量增益 高斯脉冲 束腰}     

电子在紧聚焦激光束中加速的最佳入射

通过数值模拟研究了电子在真空紧聚焦激光束中的动力学行为和能量增益。研究发现对应于两种不同的轨迹，电子可以得到纵向和横向两种电场的加速。阐明了电子的能量增益与电子的入射角和入射动量间的关系。对于给定的激光参数，给出了电子的最佳入射参数。     

High-order harmonic generation in a tightly focused laser beam

The force due to the transverse magnetic field of a laser beam drives an electron in the direction of laser propagation, thereby impeding the recollision mechanism for high-order harmonic generation. The longitudinal electric field component of a tightly focused Gaussian beam can sufficiently counteract the magnetic force to enhance the harmonic yield substantially. For tight focusing and a laser intensity of 10(18) W/cm2, it can raise the harmonic yield by several orders of magnitude.     

Flow-induced beam steering in a single laser hot spot

The transmitted angular distribution of a 527 nm nearly diffraction-limited laser is measured after it propagates through a plasma with supersonic transverse flow. The laser beam is deflected by as much as 10 degrees and exhibits bowlike features in the flow direction, which is attributed to flow-induced beam steering. The finite interaction volume allows for direct comparison with a 3D hydrodynamic simulation, which is in good agreement with details of the experiment.     

Light propagation in two-dimensional photonic crystals illuminated by a tightly focused laser beam

By using a tightly focused laser beam, we have studied light propagation in two-dimensional photonic crystals consisting of closed-packed hexagonal arrays of polystyrene particles with diameter of 1∼5 μm. The light propagation is found to depend strongly on the focal point positioning, the incident beam polarization and the interaction between particles and glass substrates.     

Reconstruction of source-field distribution of a diode bar laser beam by simulated annealing

A method for the simulation and optimization of the source-field distribution of a diode bar laser (DBL) beam by using the stimulated annealing and experimental data in the far field is proposed and illustrated by an example of a DBL JOLD-60-CPNN-1L, showing the applicability of the method. As compared with the previous models, this method is not restricted to the type of diode lasers (DLs), and the reconstructed results are accurate so long as the experimental data are sufficiently accurate.     

环形光斑激光束在非线性克尔介质中的分束现象

对于非线性克尔介质中的环形斑调制光束,通过数值求解非线性Schrdinger方程,发现当入射光强度超过一定值时,光束在传输过程中发生分束现象.对光分束的阈值、光分束与环半径及半宽度的关系、分束光的特点,以及自聚焦焦点上光强度的横向分布与光分束之间的关系进行了详细的讨论 关键词： 环形光斑 克尔介质 非线性传输 光分束     

具有波纹调制激光光束的准聚焦特性

采用光波的衍射积分理论,对具有波纹调制激光束的准聚焦特性进行了理论分析。针对中频率段畸变激光束的准聚焦特性,数值模拟研究了准聚焦光斑能量集中度、焦斑光强分布与光束波前调制周期和离焦距离的关系,并得出适当离焦距离有利于控制焦斑大小,增大激光束波前的调制周期,可增加准聚焦光斑能量集中度,降低焦斑光强的调制起伏。     

湍流大气中激光聚焦光束后向散射的数值模拟

 对基于聚焦光束后向散射到达角起伏的湍流测量进行了数值模拟。通过近轴标量波动方程和分形相屏算法,提出了聚焦光束二次传输的数值模型,分别就固定点信标光源和聚焦光束后向散射的到达角起伏方差的统计特征进行了分析,并取得了很好的相关性,得出了可以从聚焦光束的回波图像信号里提取大气湍流信息的结论。讨论了聚焦距离对固定点光源和回波光束的到达角起伏方差相似度的影响。     

IR multiple-photon dissociation by a focused uniform beam

An improved analytical method is presented in which the reaction yield in the IR multiple-photon dissociation by a focused uniform beam is expressed in a generalized form as a function of fluence. The analytical solution is derived for a real focusing geometry by assuming the cumulative log-normal distribution (CLND) for the functional form of the dissociation probability vs. fluence. Also presented is a shortcut analytical method with simple and convenient algebraic expressions which approximate the exact analytical solution, thereby speeding up the analysis of experimental data.     

Ionization of atoms by the spatial gradient of the pondermotive potential in a focused laser beam

Ionization of atoms by the spatial gradient of the pondermotive potential in a focused laser beam is investigated. Rydberg ions, formed during the interaction of noble gas atoms with an intense laser pulse, are used to probe the gradient field. Rydberg ion species with higher ionization potentials are produced at locations where the gradient field is largest. The measured Rydberg ion yields differ dramatically from estimates that ignore gradient-field ionization, but are in good agreement with predictions that include the effect.     

Determining of dark line positions on laser beam spot

Dark mode spectroscopy measurement provides accurate values of refractive index and thickness of thin film. This paper shows that precise determination of the positions of dark lines improves the accuracy of determination of listed quantities by one order of magnitude. Such improvement is of great importance for experimental studies and applications in the area of integrated optics.     

Interferometry of a single nanoparticle using the Gouy phase of a focused laser beam

We provide a quantitative explanation of the mechanism of the far-field intensity modulation induced by a nanoparticle in a focused Gaussian laser beam, as was demonstrated in several recent direct detection studies. Most approaches take advantage of interference between the incident light and the scattered light from a nanoparticle to facilitate a linear dependence of the signal on the nanoparticle volume. The phase relation between the incoming field and the scattered field by the nanoparticle is elucidated by the concept of Gouy phase. This phase relation is used to analyze the far-field signal-to-noise ratio as a function of exact nanoparticle position with respect to the beam focus. The calculation suggests that a purely dispersive nanoparticle should be displaced from the Gaussian beam focus to generate a far-field intensity change.     

Reflected image of a strongly focused spot

We describe the reflection of a strongly focused beam from an interface between two dielectric media. If the beam is incident from the optically denser medium, the image generated by the reflected light is strongly aberrated. This situation is encountered in high-resolution confocal microscopy and data sampling based on solid immersion lenses and oil immersion objectives. The origin of the observed aberrations lies in the nature of total internal reflection, for which there is a phase shift between incident and reflected waves. This phase shift displaces the apparent reflection point beyond the interface, similarly to the Goos-H?nchen shift.     

激光辐照热力耦合问题的相似性

由量纲理论出发,分析了激光辐照热力耦合理论的无量纲化基本方程组。在一定的近似条件下,导出了激光辐照热力耦合问题的一般相似性准则,该相似准则不受与温度相关的材料特性的约束。在此基础上给出了强激光辐照充压圆柱壳体热力效应的缩比方法,并对一组实例进行了计算,得到了缩比模型与原型结果几乎完全相似的结论。理论分析与数值计算表明,激光辐照热力耦合问题在合理的近似下满足相似律。     

激光辐照热力耦合问题的相似性

 由量纲理论出发,分析了激光辐照热力耦合理论的无量纲化基本方程组。在一定的近似条件下,导出了激光辐照热力耦合问题的一般相似性准则,该相似准则不受与温度相关的材料特性的约束。在此基础上给出了强激光辐照充压圆柱壳体热力效应的缩比方法,并对一组实例进行了计算,得到了缩比模型与原型结果几乎完全相似的结论。理论分析与数值计算表明,激光辐照热力耦合问题在合理的近似下满足相似律。