共查询到20条相似文献,搜索用时 15 毫秒
1.
Yongzhong Huang Jinghua Han Guoying Feng Liming Yang Qiuhui Zhang Yaguo Li Qihua Zhu 《Optik》2010,121(24):2213-2216
The experimental results show that if the pulse energy is low, the damage does not occur and the corresponding transmissivity is 100%. But with the increase of the pulse energy, the damage occurs and the transmissivity decreases to between 100% and 50%, equal to 50% and lower than 50%.The concept of the cut-off time (Tcut) is proposed to give the physics explanation on it, and by taking the free electron density (FED) and the laser-induced damage threshold (LIDT), mathematical simulation of the change law of the Tcut and the corresponding energy transmissivity with the laser energy has been done, respectively. The analysis results indicate that the former definition method can predict all the situations successfully, but the second one cannot predict the situation of the transmissivity being between 100% and 50%, the reasons of this difference also be analyzed. 相似文献
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I.IntroductionThegenerationofacousticpulsebylaserirradiationofametalsurfacewasfirstsuggestcdbyWhitein1963[1l.SincethatdateLaserU1trasoundtechniquchasbeendcvclopedrapidly.Becausethistechniquehasanumberoftechnicalfcatures,suchasnon-contact,highbandwidth,highhme-spacia1resolution,quantitativeteshng,generationoflongitudinal,shcarandRay1cighwaves(simu1taniously),andsoon,ithasbccnwidelyapp1icdtomcasurementsofmatcrialproperties,detectionofdefects,andcalibrationoftransd.ccrsl'-'o].Inordertodcve1opth… 相似文献
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T. V. Panova V. S. Kovivchak V. I. Blinov K. O. Sharifulin 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2011,5(2):347-349
Metal systems based on aluminum and copper coated with nickel irradiated by a high-power ion beam of nanosecond duration have
been studied by scanning electron microscopy and local X-ray microanalysis. Dispersed particles of micro- and nanosizes have
been found on the surface target. Their composition and formation mechanism differ. It has been shown that microparticles
were formed during mixing of film and target atoms and consisted of corresponding components. Nanoparticles were mainly composed
of the coating material, and their formation was associated with the dispersion of the Ni film due to the presence of a thin
oxide layer on the sample surface. The deposition of Ni ablated by a high-power ion beam can affect the formation of nanoparticles. 相似文献
4.
宽频带激光驱动器中光束的传输与常规的窄带系统有很大区别。数值分析了宽带激光的成像这一非线性传输现象,并与窄带激光的成像特性进行了比较,发现宽带激光的热像位置和窄带激光基本相同,但宽带激光的热像强度比窄带激光低很多,说明宽带激光能很好地抑制非线性成像的形成。此外,通过改变脉冲啁啾和脉冲宽度两种方式分别揭示了带宽对非线性成像和光束匀滑的影响,发现不同带宽情形下热像的位置基本相同,均处于共轭位置处;热像的光强和热像处光束的调制对比度随着啁啾值的增大而降低,随脉冲宽度的增大而增大。由于受到群速度色散效应的作用,带宽能够阻碍热像的形成,并提高光束的匀滑度。 相似文献
5.
宽频带激光驱动器中光束的传输与常规的窄带系统有很大区别。数值分析了宽带激光的成像这一非线性传输现象,并与窄带激光的成像特性进行了比较,发现宽带激光的热像位置和窄带激光基本相同,但宽带激光的热像强度比窄带激光低很多,说明宽带激光能很好地抑制非线性成像的形成。此外,通过改变脉冲啁啾和脉冲宽度两种方式分别揭示了带宽对非线性成像和光束匀滑的影响,发现不同带宽情形下热像的位置基本相同,均处于共轭位置处;热像的光强和热像处光束的调制对比度随着啁啾值的增大而降低,随脉冲宽度的增大而增大。由于受到群速度色散效应的作用,带宽能够阻碍热像的形成,并提高光束的匀滑度。 相似文献
6.
A theoretical solution is proposed to predict acoustic waves generated in a homogeneous and isotropic hollow cylinder by a laser line source under either ablation or thermoelastic regime. The Fourier series expansion is introduced for one spatial coordinate to solve this transient response problem. Theoretical displacements are obtained in both regimes for aluminum hollow cylinders with various thickness including a rod of the same size. The corresponding displacements are observed experimentally by the laser ultrasonic technique. Agreement has been found in the time arrival, shape and relative amplitude of surface waves and various longitudinal and transverse bulk waves. These acoustic waves are further identified by the ray trajectory analysis. This work will be helpful when dealing with the inverse problem of the nondestructive evaluation of hollow cylindrical parts. 相似文献
7.
A. A. Andreev I. A. Litvinenko K. Yu. Platonov 《Journal of Experimental and Theoretical Physics》1999,89(4):632-639
The possibility that fast electrons can escape in a direction close to the trajectory of a reflected ultrashort laser pulse
at extremely high laser radiation fluxes is examined analytically and numerically. Analytic estimates are made of the feasibility
of forming electron bursts in the plasma and of their subsequent motion. The self-consistent, collisionless motion of a plasma
acted on by specified incident and reflected ultrashort laser pulses is modeled in two dimensions by the particle-in-cell
method. It is shown that a substantial number of electrons located in the subcritical region are gathered into bunches by
the resultant forces and escape to the vacuum in a direction different from the normal to the target surface within a narrow
range of solid angles. This demonstrates the feasibility of laser acceleration of an electron burst during reflection of an
ultrashort laser pulse from a solid target.
Zh. éksp. Teor. Fiz. 116, 1184–1197 (October 1999) 相似文献
8.
F. Kh. Mirzoev 《Technical Physics》1998,43(8):943-947
A model is proposed for the ignition of a defect-density switching wave in a crystal by powerful laser pulses. It is shown
that the switching wave arises as a result of the nonlinear dependence of the activation energy of the defect-formation process
on the strain field due to defects. The conditions under which a switching wave arises and the profile, velocity, and propagation
direction of the wave are discussed.
Zh. Tekh. Fiz. 68, 73–77 (August 1998) 相似文献
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We demonstrated the interaction of a gold cone target with a femto second(fs) laser pulse above the relativistic intensity of 1.37×10 18 μm 2 W/cm 2.Relativistic electrons with energy above 2 MeV were observed.A 25%-40% increase of the electron temperature is achieved compared to the case when a plane gold target is used.The electron temperature increase results from the guiding of the laser beam at the tip and the intense quasistatic magnetic field in the cone geometry.The behavior of the relativistic electrons is verified in our 2D-PIC simulations. 相似文献
11.
A solitary structure of quasi-static electromagnetic pulse is formed in moderate density plasmas by a propagation of ultra-intense
and ultra-short laser pulse, which is formed after the laser pulse is depleted and slowly propagates in the laser propagation
direction. The structure is sustained by huge magnetic pressure and compensating electric field which are in an electromagnetic
equilibrium together with the plasma motion. The solitary structure is formed when the resonance condition is satisfied and
laser intensity is high enough to induce huge magnetic field pressure. 相似文献
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Pan Y Perton M Audoin B Rossignol C 《The Journal of the Acoustical Society of America》2006,119(1):243-250
A three-dimensional (3D) model is presented to predict the acoustic waves generated by a laser point pulse in a transversely isotropic cylinder. The Fourier series expansion and the two-dimensional Fourier transform are introduced to calculate the 3D transient response under either the ablation or the thermoelastic generation. The presented physical model and the numerical inverse scheme are applied to a fiber reinforced composite cylinder with a strong anisotropy. Experimental radial displacements of the cylinder surface are detected by the laser ultrasonic technique and analyzed by the ray trajectories for both generation regimes. Corresponding theoretical displacements are obtained numerically and compared to the experimental signals. Good agreement is found between theoretical and experimental results. The focusing effects that anisotropy gives rise to are observed in both theory and experiment under either regime. 相似文献
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A model of formation of ultradisperse particles in the plasma torch emerging during evaporation of a metal target by a high-power
electron beam is described. A model of heterogeneous media is proposed for describing the plasma torch dynamics taking into
account heat conduction, heat transfer and friction between components, relaxation of components to equilibrium, condensation,
and evaporation and coagulation of drops as a result of their collisions. Numerical simulation of the generation of ultradisperse
particles in the plasma torch formed during irradiation of a metal target by a powerful electron beam is performed. The size
distribution of ultradisperse particles is obtained for various regimes of irradiation and cooling. 相似文献
19.
V.P. Kandidov N. Akozbek M. Scalora O.G. Kosareva A.V. Nyakk Q. Luo S.A. Hosseini S.L. Chin 《Applied physics. B, Lasers and optics》2005,80(2):267-275
We propose a new method for controlling randomly generated multiple filaments during the propagation of femtosecond laser pulses in optical media. The method is based on introducing a periodic amplitude modulation of the transverse beam profile. It is shown both experimentally and numerically that the introduction of a periodic mesh into a propagation path of a femtosecond near-infrared laser pulse leads to a deterministic spatial distribution of multiple filaments in the presence of initial random fluctuations. As a result, the number of filaments is increased as compared to the random case. PACS 42.65.Jx; 42.25.Bs; 42.60.Jf 相似文献