Erosion of solid surface under irradiation by high-power submicrosecond ion beams

The erosion of a solid surface under high-power pulsed ion beams is considered. The values of atom yield from an irradiated surface due to the evaporation are obtained by numerical simulation. The effect of beam parameters and target characteristics on atom emission intensity was investigated. The technological capabilities of high-power submicrosecond ion beams for solid surface etching are assessed.     

高功率离子束的应用研究

 给出用“闪光二号”加速器高功率离子束轰击19F靶产生6~7MeV准单能脉冲γ射线的实验结果；提出采用离子束传输法分离和降低轫致辐射干扰的方法，利用闪烁体探测器和半导体探测器，测出质子传输不同距离后轰击C₂F₄靶产生的6~7MeV准单能脉冲γ射线信号以及相比轫致辐射的延迟时间；介绍了模拟材料的软X射线的热 力学效应等方面的高功率离子束的应用，给出一些实验和理论计算结果。     

超短脉冲复宗量厄米高斯光束

从超短高斯脉冲光束出发,根据复宗量厄米函数的性质,用理论解析推导的方法,给出了一组新的超短脉冲光束的解析解,称为超短复宗量厄米高斯脉冲光束。此脉冲光束解的每个频率分量都是复宗量厄米高斯光束,时间脉冲的形状是任意的,具有相同的衍射距离参量,并且可以描述短于一个光学周期的超短脉冲。对这种超短脉冲光束及其在自由空间中的传输过程进行了较为细致的研究,分析了超短复宗量厄米高斯脉冲光束的轴上光强、光强的横向分布、等衍射性质、脉冲极性反转、脉冲延迟等基本性质。讨论了引入缓变包络近似后出现的时空奇异性。     

超短脉冲复宗量拉盖尔-高斯光束

从超短高斯脉冲光束出发。根据拉盖尔多项式的性质,用理论解析推导的方法。给出了一组新的超短脉冲光束的解析解,称为超短复宗量拉盖尔-高斯脉冲光束。此脉冲光束解的每个频率分量都是复宗量拉盖尔-高斯光束。时间脉冲的形状是任意的,具有相同的衍射距离参量,并且可以描述短于一个光学周期的超短脉冲。对这种超短脉冲光束及其在自由空间中的传输过程进行了较为细致的研究,分析了超短复宗量拉盖尔一高斯脉冲光束的轴上光强、光强的横向分布、衍射性质、脉冲极性反转、脉冲延迟等。讨论了引入缓变包络近似后出现的时空奇异性。     

Propagation of ultrashort pulsed beams in dispersive media

Starting from the Rayleigh diffraction integral, the propagation equation of ultrashort pulsed beams in dispersive media is derived without making the paraxial approximation and slowly varying envelope approximation (SVEA). The spatiotemporal properties of ultrashort pulsed beams in dispersive media, such as spectrum redshifting, narrowing and pulse distortion are illustrated with pulsed Gaussian beams. It is stressed that the “antibeam“ behaviour of ultrashort pulsed beams can be avoided, if a suitable truncation function is chosen.     

超短脉冲复宗量辛格高斯光束

利用理论解析推导的方法，在傍轴近似条件下，给出了一组新的超短脉冲光束的解析解，称为超短脉冲复宗量辛格高斯光束.此脉冲光束解的每个频率分量都是复宗量高斯光束，时间脉冲的形状为辛格函数.对这种超短脉冲光束及其在自由空间中的传输过程进行了较为细致的研究，讨论了超短脉冲复宗量辛格高斯光束的轴上光强、光强的横向分布、脉冲极性反转、脉冲延迟等性质. 关键词： 脉冲光束 缓变包络近似 脉冲传输     

Distinctive features of a pulsed beam scattering on a plane surface (two-dimensional case)

A two-dimensional problem of scattering of pulsed beams having arbitrary time and spatial form on a plane surface of a lossy dielectric halfspace is solved. A pulsed beam has been modeled by letting an E- or H-polarized plane pulse with homogeneous front pass through a space filter. The reflected pulse is found using an expansion of the incident pulsed beam over time-harmonic plane waves.     

Spectral anomalies of pulsed Hermite-cosh-Gaussian beams focused by an aperture lens

The spectral behaviors of pulsed Hermite-cosh-Gaussian (HChG) beams focused by an aperture lens are studied. The propagation equation for the power spectra of pulsed HChG beams focused by an aperture lens is derived and used to study the spectral anomalies of pulsed HChG beams in the focused field. Numerical results are given to illustrate the dependence of spectral anomalies behavior on the pulse parameter and truncation parameter. The potential applications of spectral anomalies of ultrashort pulsed beams in information encoding and information transmission are considered.     

等束宽超短脉冲光束的远场特性

利用角谱法和复解析信号法推导出了等束宽超短高斯脉冲光束在远场的解析传输公式及其傅里叶谱.研究了若干个甚至一个光周期数的等束宽超短高斯脉冲光束的远场特性，并与等衍射长度超短高斯脉冲光束作了比较.研究表明，等束宽超短高斯脉冲光束在远场存在脉冲展宽、光谱变窄、离轴光谱红移、轴上光谱蓝移等特性. 关键词： 角谱法 复解析信号法 等束宽超短高斯脉冲光束     

Dynamic pulsed-beam shaping using a TAG lens in the near UV

The ability to dynamically shape the spatial intensity profile of an incident laser beam enables new ways to modify and structure surfaces through pulsed laser processing. Here we describe a method to generate doughnut-shaped beams from an input Gaussian source using a tunable acoustic gradient index (TAG) lens. The TAG lens is capable of modulating between focused beams and annular rings of variable size, using sinusoidal driving frequencies. Laser micromachining is accomplished by synchronizing the TAG lens to a 355 nm pulsed nanosecond laser. Results in polyimide demonstrate the ability to generate adjacent surface features with different shapes and sizes.     

Generating intense beams of low-energy molecules

A method for obtaining intense pulsed beams of molecules possessing low kinetic energies is proposed. The method is based on the formation of a cold pressure shock (shock wave) in an intense pulsed molecular beam interacting with a solid surface, which serves as a source of the secondary beam of low-energy molecules. The proposed method was successfully used to obtain intense beams of H₂, He, CH₄, and Kr molecules with kinetic energies not exceeding 10 meV, and H₂/Kr and He/Kr beams with kinetic energies of H₂ and He molecules below 1 meV.     

Generation of intense pulsed low-kinetic-energy molecular beams

A method for the generation of intense pulsed low-kinetic-energy molecular beams is described. The method is based on the formation of a cold (≈77 K) pressure shock as a result of interaction between an intense pulsed gas-dynamically cooled molecular beam with a solid surface. The pressure shock is used as a source of a secondary beam for generating low-energy molecules. The suggested method was used to obtain intense molecular beams of H₂, He, CH₄, N₂, and Kr with kinetic energies lower than or equal to 10 meV and H₂/Kr and He/Kr molecular beams with kinetic energies of H₂ and He molecules lower than 1 meV. The energy (velocity) of molecules in low-energy beams can be controlled by varying the intensity of the initial beam or temperature in the pressure shock.     

Nonparaxial propagation of spatially and spectrally partially coherent electromagnetic Cosh-Gaussian pulsed beams

Based on the generalized Rayleigh–Sommerfeld diffraction integral, the analytical expression for 3×3 cross-spectral density matrix of nonparaxial spatially and spectrally partially coherent electromagnetic Cosh-Gaussian (ChG) pulsed beams propagating in free space is derived, and used to formulate the spectral density and spectral degree of polarization of electromagnetic pulsed beams at the z-plane. It is found that the parameters f and f_αα are the key parameters in determining the nonparaxiality of spatially and spectrally partially coherent electromagnetic ChG pulsed beams. And the decentered parameter, pulse duration and temporal coherence length can change the nonparaxial behavior of the electromagnetic ChG pulsed beams. The effect of decentered parameter, pulse duration and temporal coherence length on the spectral density and spectral degree of polarization of electromagnetic ChG pulsed beams is illustrated through numerical calculations. Propagation of nonparaxial spatially and spectrally partially coherent electromagnetic Gaussian Schell-model pulsed beams can be treated as a special case when the decentered parameter of electromagnetic ChG pulsed beams approaches to zero.     

Pulsed ion beam parameters to ensure maximum coefficients of metal surface erosion

Erosion of metal surface under pulsed ion beams is investigated using a two-phase evaporation model. The coefficients of erosion due to evaporation are calculated for aluminum, iron and copper under irradiation by submicrosecond ion beams of carbon with the initial particle energy within the range 10–1000 keV. The ion energy and ion beam current density values of the most efficient erosive impact are determined. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 31–36, May, 2007.     

Spectral anomalies of diffracted pulsed cosh-Gaussian beams in dispersive media

Starting from the Rayleigh–Sommerfeld diffraction integral, the closed-form expressions for the near- and far-field power spectra of diffracted pulsed cosh-Gaussian (ChG) beams propagating in dispersive media are derived, and the anomalous behavior of the far-field spectrum of diffracted pulsed ChG beams in dispersive media is studied. It is shown that near the phase singularities, the spectral switch may take place. The truncation parameter, decentered parameter and pulse duration of pulsed ChG beams and the dispersive property of the medium affect the behavior of the spectral switch of pulsed ChG beams.     

洛仑兹脉冲光束的复振幅包络解和复解析信号解的比较研究

使用复振幅包络表示式和复解析信号表示式推导了洛仑兹脉冲光束的传输公式. 通过具体数 值计算对脉冲光束的复振幅包络解和复解析信号解在不同带宽时的传输进行了对比研究. 数 值结果表明脉冲光束为窄带时，在传输方向轴中心的一定范围内两种解是一致的，而对于宽 带脉冲光束，复振幅包络解在轴中心较近的距离即表现出奇异性，复解析信号解才是符合物 理意义的表示式. 由数值计算得出了选择脉冲光束研究方法的条件，并从所得公式对复振幅 包络解出现奇异性的现象进行了解释. 关键词： 复振幅包络 复解析信号 窄带脉冲 宽带脉冲     

超短脉冲径向偏振光束的解析解及时空耦合效应

从超短脉冲光束的傍轴传输方程出发, 运用傅里叶变换和相关数学算符的对易性, 得到了超短脉冲径向偏振光束的解析表达式.该解可适用于任意脉冲驱动的径向偏振光束. 基于该解析表达式并结合具体例子,讨论了超短脉冲径向偏振光束在自由空间中的传输性质. 结果表明, 在传输过程中时空耦合主要体现在光束边沿的脉冲延迟. 这一效应导致了脉冲不同时间位置处横向光强分布随传输的变化, 以及脉冲前后沿关于束腰的不对称性. 本文的方法同样适用于得到超短脉冲方位角偏振光束的解析解和传输性质.     

超短啁啾脉冲光束空间奇异性的形成与消除

研究了超短啁啾脉冲光束在真空中的传输行为以及在传输过程中时空奇异性的形成. 结果表 明，对于脉冲时间较长（相对于一个光学周期）的超短啁啾脉冲光束，啁啾导致的脉冲光谱 展宽仍然会导致脉冲光束空间奇异性的出现. 脉冲啁啾比脉冲长度对脉冲光束空间奇异性的 出现影响更大. 给出了超短啁啾高斯脉冲光束在不同参数下的数值模拟、空间奇异性出现的 条件等，并用复解析信号理论消除了空间奇异性的出现. 关键词： 单周期 缓变包络近似 奇异性 啁啾脉冲     

Spectral anomalies of diffracted pulsed Bessel beams in dispersive media

Starting from the Huygens–Fresnel diffraction integral, the analytical expression for the power spectrum of diffracted pulsed Bessel beams in a dispersive media is derived and used to study the spectral anomalies of pulsed Bessel beams in the far field. Numerical results are given to illustrate the dependence of the anomalous spectral behavior on the pulse parameters, aperture parameter and dispersive properties of the medium. It is shown that, near phase singularities, anomalous spectral behavior may take place. The potential applications of spectral anomalies of ultrashort pulsed beams in information encoding and information transmission are considered.     

Spectral behavior of pulsed Bessel beams focused by a dispersive lens

Starting from the Huygens–Fresnel diffraction integral, the analytical expression for the power spectrum of pulsed Bessel beams focused by a dispersive aperture lens is derived and used to study the spectral anomalies of pulsed Bessel beams in the focused field. Numerical calculation results are given to illustrate the dependence of spectral anomalous behavior on the pulse parameters, truncation parameter and material dispersion of the lens. It is shown that near the phase singularities the spectral anomalies may take place. The potential applications of spectral anomalies of ultrashort pulsed beams in information encoding and information transmission are considered.