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1.
The Coulomb effect on a low-energy structure in above-threshold ionization spectra induced by mid-infrared laser pulses 下载免费PDF全文
We investigate the low-energy structure(LES)in the above-threshold ionization spectrum at a mid-infrared laser wavelength with a semiclassical model.Using a softened Coulomb potential(CP)and changing the softening parameter,we show that though the very low-energy structure(VLES)and high low-energy structure(HLES)are both due to the interaction between the ionic CP and the electron,the two structures have different physical mechanisms:the VLES can be attributed to the electron–ion Coulomb interaction at a rather small distance and the HLES is more likely to be ascribed to the electron–ion Coulomb interaction at a large distance. 相似文献
2.
I. Yu. Kostyukov 《JETP Letters》2001,73(8):393-397
Inverse-bremsstrahlung absorption of an intense laser field in cluster plasma is considered in the Born approximation with allowance made for electron interaction with the entire subsystem of clustered ions. The electromagnetic power absorbed in plasma is calculated for linearly and circularly polarized laser radiations. It is shown that plasma “clustering” can give rise to much more effective absorption of electromagnetic energy as a result of collisions. The collective effects (the action of the overall field of clustered ions on an electron) dominate over the elementary processes (electron scattering by individual ions in the cluster) in the course of inverse bremsstrahlung. 相似文献
3.
为了开发和改进激光诱导稳定焊接加工技术,需要通过激光辐射使电弧的导电率达到最大值。光电偶效应是控制该过程的主导因素,该过程的优化将会保证电弧的稳定性。光电偶效应提高了等离子体粒子电离的概率,从而提高了电弧的导电率。激光光子和氩原子之间的电子-原子碰撞相互作用产生了带电粒子。电离率越高,电弧的导电率就越高。为了充分利用光电偶效应,我们还应考虑工件上的光束焦点位置、光束形状和激光波长因素。 相似文献
4.
We discuss new excitation mechanisms in energetic ion-atom collisions embedded in short laser pulses. For comparable duration and strength of the pulse and collisional interaction, the laser field will probe and modify the interaction between projectile and target. Coherence effects emerge, insight into reaction dynamics is gained, and new dynamical features are discovered. As an example, we show (i) how a propensity rule for s-p excitation can be dramatically changed, and (ii) how the presence of the laser pulse modifies the ionization process in ion-atom collisions. 相似文献
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当采用低功率的宏-微脉冲激光激发钠信标时, 尽管激光传输和钠信标光斑大小受到大气湍流影响, 但是钠信标具有回波光子数无起伏且激发品质因数高的优点. 除此之外, 宏-微脉冲激光激发钠信标还与激光的宏脉冲线型有关. 对于高斯线型的宏脉冲, 增大微脉冲的宽度有利于提高激发钠信标的品质因数和激发态概率. 为了获得更多的钠信标回波光子和较小的钠信标半径, 增大激光功率的同时要考虑良好的光束质量、适当的激光发射口径以及光谱宽度等影响因素. 因此, 优选宏-微脉冲激光的参数、发射口径、发射方式等对于激发优良特性的钠信标有着重要的现实意义. 相似文献
7.
A. V. Kozlovskii 《Journal of Experimental and Theoretical Physics》2003,96(6):993-1005
A self-consistent quantum theory is developed for an atomic laser utilizing cooling of atoms in a trap by the method of stimulated evaporation. The model describes the pumping and extraction of the atomic field from a trap upon its interaction with independent atomic reservoirs. The stimulated collisions between atoms in the trap, which produce a Bose condensate in the lower state of the trap, are considered. The interaction of atoms with a phonon field causes spontaneous transitions between the discrete states of the trap. Calculations performed for the three-and four-level models of the trap showed the possibility of generation of a strongly squeezed sub-Poisson Bose condensate. 相似文献
8.
L.D. Pietanza G. Colonna S. Longo M. Capitelli 《Applied Physics A: Materials Science & Processing》2004,79(4-6):1047-1050
A theoretical investigation of the electron and phonon time-dependent distributions in an Ag film subjected to a femtosecond laser pulse has been carried out. A system of two coupled time-dependent Boltzmann equations, describing electron and phonon dynamics, has been numerically solved. In the electron Boltzmann equation, electron–electron and electron–phonon collision integrals are considered together with a source term for laser perturbation. In the phonon Boltzmann equation, only electron–phonon collisions are considered, neglecting laser perturbation and phonon–phonon collisions. Screening of the interactions has been accounted for in both the electron–electron and the electron–phonon collisions. The results show the simultaneous electron and phonon time-dependent distributions from the initial non-equilibrium behaviour up to the establishment of a new final equilibrium condition. PACS 72.10.-d; 71.10.Ca; 63.20.Kr 相似文献
9.
In CO2 laser gas-assisted cutting process, modeling of the interaction mechanism is important. Consequently, the present study treats the complete problem of the interaction of the melting surface with the boundary layer and describes the behavior of the melting layer. In the analysis, gas–liquid interface parameters are developed and relationships between the parameters influencing the cutting action are identified theoretically. To achieve this, effects of momentum and gas–liquid interface shear stress, due to the assisting gas jet, are considered. The approximate magnitude of the heat absorbed is estimated and melting layer thickness is predicted. An experiment is carried out and the theoretical predictions are compared with the experimental findings. First and second law efficiencies of the cutting process are predicted, which may, then, be used to improve the process. It is found that the assisting jet velocity increases the first and second law efficiencies of the CO2 laser cutting process. 相似文献
10.
Felix Shapirov 《Journal of statistical physics》1995,78(1-2):413-430
The behavior of a mixture of optically excitable and inactive gases in the field of a laser radiation is considered from the viewpoint of nonequilibrium thermodynamics. The kinetic coefficients satisfying the Onsager-Casimir reciprocity relations are found from general properties of the Boltzmann equation, boundary condition, and terms describing the gas-radiation interaction. Various kinetic phenomena induced by the laser radiation are coupled with corresponding cross effects. 相似文献
11.
The surface reaction on titanium due to pulsed Nd:YAG laser irradiation in a nitrogen atmosphere was investigated using X-ray photoelectron spectroscopy (XPS). The laser, with a wavelength of 532 nm (SHG mode), was irradiated on a titanium substrate in an atmosphere-controlled chamber, and then the substrate was transported to an XPS analysis chamber without exposure to air. This in situ XPS technique makes it possible to clearly observe the intrinsic surface reaction. The characteristics of the surface layer strongly depend on the nitrogen gas pressure. When the pressure is 133 kPa, an oxynitride and a stoichiometric titanium nitride form the topmost and lower surface layers on the titanium substrate, respectively. However, only a nonstoichiometric titanium oxide layer containing a small amount of nitrogen is formed when the pressure is lower than 13.3 kPa. Repetition of laser shots promotes the formation of the oxide layer, but the formation is completed within a few laser shots. After the initial structure is formed, the chemical state of the surface layer is less influenced by the repetition of laser shots. 相似文献
12.
脉冲激光在有机分子材料中的共振传播 总被引:3,自引:3,他引:0
利用麦克斯韦-布洛赫耦合方程,研究了激光脉冲在4,4′-二甲氨基二苯乙烯分子材料中的共振传播,探讨了激光脉冲在传播中的时空演化情况.在数值计算中考虑了各种阻尼效应. 相似文献
13.
Laser materials processing is highly affected by the existence of surface plasma. The absorption of surface plasma during drilling alters the power intensity distribution of the incident laser beam across the irradiated spot. The present study is carried out to measure the electron number density and temperature using a Langmuir probe while a mathematical formulation is conducted for the absorption coefficients due to electron-ion, electron-neutral atom collisions, inverse Bremsstrahlung, and photoionization processes. Consequently, a computer program is developed to compute the relevant absorption coefficients as well as the overall absorption coefficient. The laser power intensity distribution before and after the plasma absorption is computed at a plane 2.6 mm above the workpiece surface. It is found that 13% of the reduction occurs in the incident laser output power intensity at this plane in the plasma. 相似文献
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Alexander Pyatenko Hongqiang Wang Naoto Koshizaki Takeshi Tsuji 《Laser \u0026amp; Photonics Reviews》2013,7(4):596-604
The laser is a very powerful and very useful instrument in modern nanoscience and nanotechnology. The knowledge of the interaction mechanism of the laser beam with nanoparticles is needed to control the laser processing of different nano‐objects. It was shown that the particle heating–melting–evaporation model can be successfully applied for many phenomena arising when colloidal nanoparticle interact with pulsed laser beams. The general approach of this model is discussed in detail. The two main components of the model, light absorption by particles, and the thermodynamics of phase transitions in particulate material are considered. Special attention is devoted to the correct estimation of the possible heat losses. The way in which the phase diagrams, where the different phase conditions of particle material are presented in laser fluence−particle diameter coordinates, were produced is demonstrated. It is shown how this model can be applied for understanding the mechanism of such complicated processes as particle‐size reduction and submicrometer spherical particle growth, as well as other processes that occur when colloidal particles are irradiated by a pulsed laser. 相似文献
16.
A study of ultrafast electron diffusion kinetics in ultrashort-pulse laser ablation of metals 总被引:1,自引:0,他引:1 下载免费PDF全文
Temperature dependence of the electron diffusion in metallic targets,
where the electron--electron collision is the dominant process, is
investigated with the help of an extended two-temperature model. In
sharp contrast to the low electron temperature case, where only the
electron---phonon collisions are commonly considered, the electron
diffusion process underlying the high electron temperatures evolves
dramatically different in both temporal and spatial domains.
Calculated results of the ablation yield at different pulse durations
are presented for a copper plate impinged by ultrashort laser pulses
with energy fluences ranging from 0.1 J/cm2 to 10 J/cm2.
The excellent agreement between the simulation results and the
experimental data indicates the significant role of
electron--electron collisions in material ablations using intense
ultrashort laser pulses. 相似文献
17.
I. N. Kosarev 《Technical Physics》2007,52(7):934-936
Interaction between a picosecond laser pulse of nonrelativistic intensity with a thin target is studied in terms of the kinetic theory of laser plasma, which is based on constructing propagators for the plasma particle distribution functions. Allowance is made for both the self-consistent plasma field and plasma particle correlations (collisions). The interaction causes charge separation in the target and strong heating of electrons. 相似文献
18.
在压缩真空态光场和二能级原子玻色-爱因斯坦凝聚体相互作用系统中, 应用全量子理论, 分别在旋波近似和非旋波近似下, 研究了原子激光的压缩特性以及原子本征频率、光场-原子的耦合系数、光场初始压缩因子以及虚光场对原子激光压缩特性的影响. 研究表明,原子激光的两个正交分量均可被周期性压缩,原子的本征频率决定了原子激光两个正交分量涨落的量子Rabi频率,光场与原子的耦合系数决定了原子激光正交分量涨落的崩塌-回复振荡频率,当光场初始压缩因子增大和考虑虚光场效应时,原子激光正交分量的压缩深度均加深.
关键词:
玻色-爱因斯坦凝聚
压缩真空态
原子激光
虚光场效应 相似文献
19.
Kuchiev MY 《Physical review letters》2007,99(13):130404
A strong laser field and the Coulomb field of a nucleus can produce e(+) e(-) pairs. It is shown for the first time that there is a large probability that electrons and positrons created in this process collide after one or several oscillations of the laser field. These collisions can take place at high energy, resulting in several phenomena. The quasielastic collision e(+) e(-) --> e(+) e(-) allows acceleration of leptons in the laser field to higher energies. The inelastic collisions allow production of high-energy photons e(+) e(-) --> 2 gamma and muons e(+) e(-) --> micro(+) micro(-). The yield of high-energy photons and muons produced via this mechanism exceeds exponentially their production through conventional direct creation in laser and Coulomb fields. A relation of the phenomena considered with the antenna mechanism of multiphoton absorption in atoms is discussed. 相似文献
20.
Simulations of particles which are emitted in laser ablation have been performed by the method of Direct Simulation Monte Carlo to investigate the deposition profiles of the emitted particles. The influences of the temperature, pressure and stream velocity of the initial evaporated layer formed during laser ablation process on the profile of the deposited film have been examined. It is found that the temperature gives a minor influence on the deposition profile, whereas the stream velocity and the pressure of the initial evaporated layer have a greater impact on the deposition profile. The energy in the direction of surface normal (E⊥) and that in the parallel direction of the surface (E||) are shown to increase and decrease, respectively after the laser irradiation due to collisions between the emitted particles, and this trend is magnified as the pressure increases. As a consequence, the stream velocity in the direction of surface normal increases with the increase in the pressure. A mechanism of the phenomenon that a metal with a lower sublimation energy shows a broader angular distribution of emitted particles is presented. It is suggested that low density of evaporated layer of a metal with a low sublimation energy at its melting point decreases the number of collisions in the layer, leading to the low stream velocity in the direction of surface normal, which results in the broader deposition profile of the emitted particles. 相似文献