原子纳米光刻中双层光学掩膜的实现方法研究

利用原子光刻的方法制备纳米结构的光栅已经成为了一种较为成熟的工艺。通过原子与激光驻波场的相互作用,利用原子自生在势能场中的偶极力对原子的密度进行调制,从而得到所需要的光栅结构。利用此种工艺所制备的光栅相对于传统工艺来说具有精度高,光栅常数直接溯源于原子能级。希望能够通过对激光的改良来提升原子沉积结果。通过双层驻波场来提高原子沉积质量已经被多次提到。实验中利用几何光学的方法实现了所需要的新型激光驻波场。并对其汇聚,相干等特性进行了研究,取得了较为满意的结果。为利用双层驻波场来沉积原子打下了基础。     

氦原子在超短中红外脉冲和极紫外光场作用下的双电离（英文）

利用数值求解含时薛定谔方程的方法研究了氦原子在超短红外激光脉冲和极紫外激光场作用下的双电离过程。在此过程中,一个电子首先被极紫外激光场电离,然后氦离子既可以被接下来的红光激光场直接隧穿电离,也可以被红外激光场驱动下的电子再散射而发生非次序双电离。这两种双电离通道的干涉可以产生新颖的电子关联动量谱分布。当驱动红外激光脉冲为周期量级时,再散射导致的双电离的两个电子的运动方向可以相同,也可以相反。     

光通过色散介质反向散射的角度各向异性和脉冲动力学

本文给出均匀介质在光源方向散射的光脉冲时间形状的测量和模型计算的结果。对于具有激活同步模的氩激光脉冲研究了接近“后向”方向的散射动力学,氩激光脉冲在乳液微型粒子的水溶液中传播,研究是用光子计数时间相关的方法进行的。确立了反向散     

全尺寸目标激光脉冲后向散射回波功率测定和建模

运用粗糙面散射、激光脉冲散射理论,结合复杂目标粗糙表面相关建模参数,建立用于计算全尺寸复杂目标激光脉冲后向散射功率的理论模型.实验测量一种空中缩比目标模型后向散射激光脉冲回波功率,获取该缩比目标激光脉冲后向散射功率随接受天顶角的变化曲线.比较理论建模与实验测量数据,分析实验误差,证明了该理论模型的正确性.将建立的理论模型进一步应用于计算非合作空间全尺寸目标的激光脉冲回波功率.计算结果能够预估空间目标的激光散射特征,解决一些关于空间目标激光脉冲光学特征工程的应用问题.     

锥形超强激光场中光子康普顿散射的能量转换

应用相对论性电子与光子非弹性碰撞模型和经典相对论电动力学理论，分析、计算了锥形超强激光场中的电子和光子的能量转换效率，得出了用高能电子束与发生单光子非线性Compton散射是提高二者能量转换效率的理想途径的结论。     

紧聚焦强激光脉冲中电子的非对称性辐射

为了获得紧聚焦脉冲激光作用下电子的辐射特性,采用非线性Thomson散射理论和线偏振紧聚焦激光脉冲与单电子的相互作用模型,利用MATLAB完成数值模拟,获得了电子的运动特性、不同观测角度下的功率与能量分布,以及最大辐射方向上的功率与能量.结果表明,与平面波激光脉冲作用下的非线性Thomson散射现象相似而又不同,在紧聚...     

原子激光

激光问世以来以其高强度高单色性在科学和技术中获得广泛应用 ,改变了整个光学的面貌 ,特别是在世界通信网中起了主导作用。激光器、光放大器和光电子元件每年的产值达到数十亿美元。原子物理学家也在期待原子激光的发明会导致原子光学或物质波光学的一场革命。基于光波与物质波的类同性 ,像光学那样 ,原子的透镜、反射镜和分束器也能控制原子束。现在 ,关键是要实现这种高强度、高方向性具有同一波长的相干原子束 ,即原子激光。玻色 -爱因斯坦统计　　原子激光基于稀释气体的玻色 -爱因斯坦凝聚体的量子特性。只是在 1995年首次发现这种凝…     

基于蓝绿激光雷达的海洋赤潮探测方法研究

对基于蓝绿激光的海水光学传输信道特性进行了分析,提出了利用蓝绿激光雷达探测海洋赤潮的新方法。利用蓝绿激光具有较强的海水透过性,可以获取较深海域的赤潮信息。通过检测海水中蓝绿激光的后向散射信号,可以实现对海洋赤潮密度信息的获取。在分析海洋赤潮粒子吸收和散射特性的基础上,建立了基于蓝绿激光雷达的海洋赤潮密度探测模型。通过仿真计算,证明该模型可以有效探测出海洋赤潮密度的大小,进而可以实现对海洋赤潮消长过程的监测和预报。     

会聚圆偏振强激光场中的原子离化理论

近几年来,强激光场作用下的原子行为,特别是在激光场中原子离化过程的研究吸引了很多人的兴趣。理论上,在处理原子离化问题时,一个很重要的问题是怎样处理有激光场存在时的电子离化态。最早的KFR模型采用忽略原子库仑势对离化电子的作用后的平面波形式的Volkov解。随后,一些研究者在考虑了原子库仑场的影响后,得到了离化电子波函数的类Volkov的库仑连续态,并在此基础上处理了原子离化问题。     

超短强激光脉冲大气传输效应建模

超短脉冲强激光大气传输在光学遥感、电子对抗以及人工放电等方面具有重要的应用,对超短脉冲强激光在大气中的传输进行了理论分析,对超短脉冲强激光大气传输中各种线性效应及非线性效应。诸如色散效应、非线性自聚焦效应、受激拉曼散射效应、多光子电离及隧道电离效应、电离引起的能量损耗效应、相对论聚焦、有质动力激发的等离子体尾波场等效应进行了讨论,给出了一组描述超短脉冲强激光大气传输的三维非线性传输方程,为此类问题的进一步研究提供了理论基础。     

Bistatic scattering by arbitrarily shaped objects with rough surface at optical and infrared frequencies

The scattering cross sections for arbitrarily shaped dielectric objects with rough surface are determined for optical and infrared frequencies using the Kirchhoff approximation. The formula of the coherent scattering cross section is derived, and numerical method of incoherent scattering cross section is given. As a specific example, the infrared laser scattering cross sections of rough spheres are calculated at 1.06 μm.     

Observation of the anisotropy of the inelastic scattering of fast electrons accompanied by the K-shell ionization of a carbon nanotube

The angular distribution of inelastically scattered electrons following the carbon K-shell ionization of a carbon nanotube (CNT) has been studied by using an energy-filtered transmission electron microscope. The energy-filtered scattering patterns of the CNT, whose cylindrical axis is oriented in the perpendicular direction with respect to the incident-electron beam, show anisotropic angular distributions caused by the p symmetry in the pi* and sigma* unoccupied states into which a K electron jumps, and the cylindrical shape of the CNT. Corresponding inelastic scattering cross sections, differential in solid angle, have been calculated within the first Born approximation by considering that each carbon atom has three, mutually orthogonal, unoccupied p orbitals, which are oriented in directions perpendicular or parallel to the tube surface. The observed angular patterns agree well with theoretical results, which are linear combinations of the differential cross sections accompanied by the transitions to pi* and sigma* states. A series of the fittings of the experimental patterns at successive values of energy loss provides magnitudes of the pi* and sigma* components, which can be called partial electron energy-loss spectra accompanied by the transitions to the pi* and sigma* states.     

Scattering of screened excitons by free carriers in semiconductingquantum well structures

The theoretical treatment of the scattering of excitons by free electrons and holes in a two-dimensional semiconducting quantum-well system is extended to take into account screening by the free carriers. The scattering cross sections are calculated using the Born approximation for elastic scattering of the excitons by the free carriers. For the heavy-hole exciton, the screening by the free carriers reduces the cross section for free-carrier exciton scattering for all values of the energy of relative motion of the free carriers and the excitors. For the light-hole exciton, however, screening can actually lead to an enhancement of the scattering cross section for low values of the energy of relative motion when the density of free carriers is high. This is because screening not only reduces the interaction between the free carriers and the exciton, but also decreases the binding of the exciton, leading to a larger effective radius of the exciton. The results for the scattering cross sections are then applied to calculate the contribution of the exciton linewidth due to elastic scattering of the excitons by free carriers. It is found that this contribution to the exciton linewidth is decreased below its value in the absence of screening for both the heavy- and light-hole excitons     

Forbidden Resonant Raman Scattering in GaAs/AlAs Superlattices: Experiment and Calculations

The Raman spectra of GaAs/AlAs(100) superlattices are calculated and studied experimentally for various wave-vector directions. The experiments are performed when applying a confocal optical microscope combined with a micro-Raman spectrometer for various scattering geometries both for phonons with a wave vector directed along the normal to a superlattice and in the in-plane geometry. The frequencies and eigenvectors of phonons are calculated in the extended Born model approximation taking into account Coulomb interaction in the rigid-ion approximation. The Raman spectra are calculated in the scope of the deformation- potential mechanism; herewith, it turns out that additional peaks, which are not described in the scope of this approach, appear in the experimental spectra. It seems likely that these peaks appear due to the manifestation of Raman scattering forbidden by selection rules under resonance conditions. An attempt is made to explain the appearance of these peaks in the experimental spectra within the scope of inelastic phonon scattering at bound charges (phonons with a large dipole moment).     

Calculations of Infrared Laser Beam Scattering from Rough Dielectric Objects

The coherent and incoherent scattering cross sections of Infrared Laser Gaussian beam scattering from arbitrarily shaped convex dielectric objects with rough surfaces are investigated by using plane wave spectrum method and physical optics approximation. In the paper, the infrared laser scattering cross sections of rough sphere are calculated at 10.6 μm , and the influence of the beam size, permittivity, and polarization as well as roughness parameters is analyzed numerically. When the beam size is much larger than the size of object, the results in the paper can reduce to those of an incident plane wave. On the other hand, for the case of roughness statistical parameter close to zero, only the forward scattering has a parent difference compared with the result of gaussian beam scattering from smooth sphere.     

Wave diffraction by a rough boundary of an arbitrary plane-layeredmedium

The problem of electromagnetic (EM) wave scattering by a slightly rough boundary of an arbitrary layered medium is solved by a small perturbation method. The bistatic amplitude of scattering as well as scattering cross sections for a statistically rough surface are calculated for linear and circular polarized waves. Along with the scattering into the upgoing waves in the homogeneous medium, the scattering cross sections in the downgoing waves into a layered medium are obtained. Analytical results are applied to the modeling of natural layered media (ice and sand layers) remote sensing problems employing global positioning system (GPS) technics     

A comparison of scattering model results for two-dimensionalrandomly rough surfaces

Bistatic radar cross sections are calculated using two modern scattering models: the small slope approximation (both first- and second-order), and the phase perturbation technique. The problem is limited to scalar-wave scattering from two-dimensional, randomly rough Dirichlet surfaces with a Gaussian roughness spectrum. Numerical results for the cross sections are compared to those found using the classical Kirchhoff, or physical optics, approximation and perturbation theory. Over a wide range of scattering angles, the new results agree well with the classical results when the latter are considered to be accurate. A comparison between the new results shows that the phase perturbation method gives better results in the backscattering region for correlation lengths greater than approximately one wavelength, while both the first- and second-order small slope approximations yield greater accuracy in the forward scattering direction at low grazing angles     

Iterative numerical computation of the electromagnetic fieldsinside weakly nonlinear infinite dielectric cylinders of arbitrary crosssections using the distorted-wave Born approximation

The electromagnetic scattering by weakly nonlinear infinite dielectric cylinders is the topic dealt with in this paper. The cylinders are assumed to be isotropic, inhomogeneous, and lossless and to have arbitrarily shaped cross sections. A time-periodic illumination of the transverse magnetic type is considered. The nonlinearity is assumed to be expressed by the dependence of the dielectric permittivity on the internal electric field, under the hypothesis that the operator responsible for the nonlinearity does not modify the scalar nature of the dielectric permittivity and produces a time-periodic output. The electromagnetic scattering is then described by an integral equation formulation, and the electromagnetic field distributions inside and outside a scatterer are approximated by an iterative numerical procedure starting with the application of the distorted-wave Born approximation. In a simplified version of the approach, the classic first-order Born approximation is used. The convergence of the approach is discussed in several examples. In the computer simulations concerning cylinders with different cross-section shapes, the effects of the nonlinearity on the field-component fundamental frequency were evaluated for different values of the nonlinear parameters in the case of a Kerr-like nonlinearity and of a uniform incident plane wave. The generation of higher-order harmonics was also considered     

Two-dimensional microwave imaging by a numerical inverse scatteringsolution

A numerical approach that aims to detect, by means of interrogating microwaves, the locations and the dielectric permittivities of unknown inhomogeneous dielectric cylindrical objects of arbitrary cross sections that might be present inside a fixed area of interest is proposed. An illumination is assumed with the electric field vector polarized along the cylindrical axis. The two-dimensional Lippman-Schwinger integral equation of electromagnetic scattering is transformed into matrix form by the moment method. The system obtained is solved by using a pseudoinversion algorithm to overcome ill-conditioning problems. The first-order Born approximation is also applied when the dielectric inhomogeneities are weakly scattering. Computer simulations have been performed by means of a numerical program. Results show the capabilities and limitations of the proposed approach     

基片表面微球体纳米级缺陷的光散射分析

为了进一步诊断反演出基片及光学元件中杂质缺陷的形态和尺寸,应用Bobbert-Vileger(BV)理论建立两种缺陷粒子的复合光散射模型,通过对场进行矢量球谐函数展开,对基片上缺陷粒子的光散射问题展开讨论,对散射场及微分散射截面进行推导求解。同时将数值计算结果退化为球形粒子与采用扩展Mie理论方法所得结果做了比较,二者吻合较好。通过数值计算考察了不同材质下,形变对微分散射截面的影响。结果表明,金属缺陷的散射更易受形变的影响,而介质缺陷受形变的影响很小。当球缺靠近基底的情况下,微分散射截面受散射角的影响较大;球缺背离基底时,几乎和球形粒子散射曲线重合,因此通过对微分散射截面的计算可以定位反演出球缺的位置和材质。