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在神光Ⅱ高功率激光装置上,实验研究了激光斜辐照形成的激光等离子体辐射X射线光子的特性及真空喷射热等离子体流的方向。采用针孔X射线相机测量了钕玻璃激光(基频1.053 μm)辐照铝靶形成的激光铝等离子体辐射的X射线光子的空间分布,并针对正入射和入射激光斜辐照情况下测得的X射线光子量及特性进行了分析和比较。结果发现:入射激光斜辐照固体平面靶产生的向真空喷射热等离子体流的方向是垂直靶面(即法线方向);正入射和斜入射激光叠加驱动靶时,一定程度上能改善激光辐照的均匀性,但等离子体源辐射的X射线光子数并未发现显著地增加;当激光斜辐照与靶相互作用时,激光能量被等离子体吸收下降。 相似文献
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《光学学报》2010,(11)
利用广义非线性薛定谔方程,研究了聚焦激光通过透明介质时,感应等离子体的位置、大小及其同激光参数的关系。计算发现:对于给定衍射长度的激光波包,感应等离子体浓度最大值随入射激光功率的增加而趋于一恒定值,感应等离子体区域的大小随着入射激光波包功率的增加而变长、变粗;对于给定功率的激光波包,感应等离子体浓度随着入射激光波包的衍射长度的增加而减少;对于不同衍射长度的激光波包,随着激光功率的增加,感应等离子体向不同方向发展。计算得到的等离子体的位置和形状的变化同Gord ienko等的实验结果非常吻合。该研究有助于理解感应等离子体在介质中的形成过程,推动其在激光加工中的应用。 相似文献
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通过二维粒子模拟(particle-in-cell)方法研究了强激光与亚临界密度等离子体相互作用中的近前向光子加速机制.该机制利用强激光在亚临界密度气体传输过程中的电离效应产生在纵向和横向上密度分布不均匀的电子等离子体.在纵向上,入射激光电离氦气产生一个陡峭的电子密度前沿分布.在密度前沿处,入射激光与电子等离子体波作用发生近前向散射.散射光频率较激光频率增大,在频谱中产生了第一个特征峰.在横向上,密度不均匀造成电子等离子体波具有不同的相速度并与入射激光相互作用,使入射激光发生近前向散射,在频谱中产生了第2个特征峰.由于密度分布的不均匀性较电子等离子体波的密度扰动大得多,因此基于微扰理论的散射模型和色散关系,如受激拉曼散射,无法解释频谱中两个特征峰的出现.进一步研究发现:在密度不均匀的情况下,入射激光、电子等离子体波和散射光三者之间仍满足动量和能量守恒的三波耦合关系.这能够解释两个特征峰对应的频率和强度增长过程.该研究对于强激光在亚临界密度气体传输过程中的频谱演化具有重要参考意义. 相似文献
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此文着重研究短脉冲强激光作用下的等离子体X射线辐射强度随入射激光能量或功率的变化,等离子体辐射主要由激光功率决定,实验显示了辐射曲线的突变区域和他和区域结构。此外,本结果表明在激光以20Ps入射条件下的等离子体相对论吸收效应还不太明显,在等离子体中主要是逆韧致吸收。 相似文献
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基于相对论性激光-等离子体动力学理论,研究了相对论性激光-等离子体系统中圆偏振入射脉冲激光和等离子体相互作用对激光脉冲宽度的影响. 具体分析了在不同初始物理参数下脉冲激光的脉冲宽度在等离子体传播过程中的变化情况,重点分析了激光脉冲在等离子中压缩. 计算结果表明增加入射激光的强度和入射脉冲宽度以及减小等离子体的初始密度,能够有效地实现脉冲宽度在等离子体中压缩;当激光脉冲的初始参数a0=0.12和τ=70以及等离子体密度n0=0.3时,脉冲宽度相对压缩T/τ接近于1/10,从而给出了激光压缩的理论优化参数.
关键词:
相对论性激光-等离子体
激光脉冲宽度
等离子体密度
自压缩 相似文献
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《等离子体物理论文集》2017,57(1):29-39
In this paper, a two dimensional Particle In Cell‐Monte Carlo Collision simulation scheme is used to examine the THz generation via the interaction of high intensity ultra‐short laser pulses with an underdense molecular hydrogen plasma slab. The influences of plasma density, laser pulse duration and its intensity on the induced plasma current density and the subsequent effects on the generated THz signal characteristics are studied. It is observed that the induced current density in the plasma medium and THz spectral intensity are increased at the higher laser pulse intensities, laser pulse durations and plasma densities. Moreover, the generated THz electric field amplitude is reduced at the higher laser pulse durations. A wider frequency range for the generated THz signal is shown at the lower laser pulse durations and higher plasma densities. Additionally, it is found that the induced current density in hydrogen plasma medium is the dominant factor influencing the generation of THz pulse radiation. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Ghazaleh Ghani-Moghadam Somayeh Rezaei Mohammad J. Jafari Amir H. Farahbod 《等离子体物理论文集》2021,61(9):e202100042
Plasmas created by the interaction of high power optical laser with a target surface can be used as a source of soft X-ray lasers. Plasma and pump laser characteristics play significant role in achieving high gain coefficient for such plasma based on soft X-ray lasers. In the present work, the plasma active medium parameters for germanium element at a wavelength of 19.6 nm irradiated by a double-pulse pump laser have been studied using MED103 hydrodynamic code. For this purpose, first, the effects of laser intensity, pulse width and delay time of two pulses on the gain coefficient have been investigated and the optimum conditions for the maximum gain extent of Ne-like germanium soft X-ray laser are obtained. Then, in order to calculate the intensity of such high gain lasers in which Linford equation is invalid, we have adopted the general formula of amplified spontaneous emission intensity, which is valid in all range of intensities even at much higher intensities than saturation intensity. Finally, the soft X-ray laser intensities in the saturated areas for different plasma lengths have been calculated. The results show that the output of soft X-ray laser intensity with 294 cm−1 gain coefficient can reach to about several times saturated intensity by applying a 1–2 mm plasma length as the active medium. 相似文献
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R. A. Ganeev 《Optics and Spectroscopy》2013,115(1):94-105
This work reviews a series of investigations of different plasma plumes using single- and two-color laser systems that emit femtosecond pulses with a 10-Hz repetition rate. Results of investigation of the resonant enhancement of harmonics in tin plasma with the use of two types of pumps are analyzed, and it is shown that the tuning of the wavelengths of harmonics to ion-resonance levels plays an important role in increasing the conversion efficiency to high-order harmonics of the radiation to be converted. Investigations of different carbon-containing plasma media (carbon nanotubes, graphite, carbon aerogel, etc.) exhibit attractive properties of the nonlinear medium of this type for efficient generation of high-order harmonics. The results of the first experiments on the use of nanoparticles produced directly in the course of laser ablation of metals for increasing the efficiency of harmonics generated in this cluster-containing medium are analyzed. It is shown that new approaches realized in these investigations give hope that the nonlinear optical response of plasma media in the far-ultraviolet range can be further increased. 相似文献
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The laser plasma formed in gaseous media due to their optical breakdown under tightly focused femtosecond laser pulses has been experimentally investigated. Pump-probemicrointerferometry is chosen to perform spatial and temporal diagnostics of the plasma. Time dependences of the laser plasma electron density are obtained. It is shown that in breakdown of different gases (air, nitrogen, argon, and helium) at different pressures (in the range from 1 to 10 atm) the electron concentration continues to increase during ??1 ps when the laser irradiation is over. This effect is related to the impact ionization of the plasma by the hot electrons formed in interaction of intense femtosecond laser pulses with matter. The results of theoretical simulation of the post-ionization processes are presented. 相似文献
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利用波长为1 064 nm,最大能量为500 mJ的Nd∶YAG脉冲激光器在室温,一个标准大气压下对Mg合金冲击,改变激光能量,得到相应的Mg等离子体特征谱线。分析谱线,发现谱线有不同的演化速率,同时得到了MgⅠ,MgⅡ离子谱线,证明此实验条件下,激光能量足够Mg合金靶材充分电离。选择了相对强度较大的MgⅠ 383.2 nm, MgⅠ 470.3 nm, MgⅠ 518.4 nm三条激发谱线,利用这些发射谱线的相对强度计算了等离子体的电子温度,激光能量为500 mJ时,等离子体温度为1.63×104 K。实验结果表明:在本实验条件下,Mg原子可以得到充分激发;在200~500 mJ激光能量范围内,等离子体温度随着激光能量的降低而衰减,在350~500 mJ激光能量范围内的等离子体温度随激光能量的变化速度十分明显,200~350 mJ时等离子体温度变化速度迅速减缓;激光能量为300 mJ时,谱线相对强度明显减弱,低于350和250 mJ的谱线相对强度,不符合谱线相对强度会随着激光能量提高而上升的变化趋势,证明发生了等离子体屏蔽现象,高功率激光产生的等离子体隔断了激光与材料之间的耦合。此时的等离子体温度明显升高,不符合变化趋势,这是由于在发生等离子体屏蔽现象时,激光能量被等离子体吸收,导致等离子体温度上升。 相似文献
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采用光栅光谱仪 对脉冲光纤激光修锐青铜金刚石砂轮过程中产生的等离子体空间分辨发射光谱进行了测量. 研究了500–600 nm波段范围内的等离子体空间发射光谱强度随激光平均功率和脉冲重复频率的变化情况. 结果表明: 等离子体辐射光谱强度在其径向膨胀方向上距离砂轮表面约2.4 mm处达到最大值. 在局部热力学平衡假设条件下, 根据等离子体中六条铜原子谱线的相对强度, 利用Boltzmann 图法, 计算得到在不同激光功率和重复频 率条件下的等离子体电子温度沿砂轮径向方向的分布规律. 实验结果表明: 在激光修锐青铜金刚石砂轮过程中, 距离砂轮表面约3 mm处等离子体电子温度出现峰值, 其温度最高可达4380 K, 且等离子体电子温度随着激光参数和 空间位置的改变呈现出不同的演变规律.
关键词:
脉冲光纤激光
等离子体发射光谱
激光修锐
电子温度 相似文献
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Olga A. Bulgakova Nadezhda M. Bulgakova Vladimir P. Zhukov 《Applied Physics A: Materials Science & Processing》2010,101(1):53-59
We report a model of nanosecond laser ablation of compound semiconductors taking into account stoichiometry loss as a result
of different volatilities of the material components. The model is based on the heat-flow equation for the bulk material and
the diffusion equation for its atomic constituents and takes into account variations of material properties as functions of
temperature and composition. Changing the optical response which results from stoichiometry violation is described within
the concept of an effective medium and a multi-layer reflection model is applied. For cadmium telluride, as an example, the
processes of ablation, melting, and resolidification under the action of a KrF laser have been studied in dynamics for particular
experimental conditions in a wide range of laser fluences from the ablation threshold to the plasma shielding regimes described
by the effective plasma plume representation. Multi-shot irradiation regimes have been investigated and the mechanism of the
irradiation-controlled stoichiometry reversal has been elucidated. 相似文献
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The interaction of an intense circularly polarized laser pulse with a layer of plasma of supercritical density is studied. The nonlinear skin effect for the electromagnetic field and the coefficient of collisionless absorption of the laser pulse were calculated analytically. It is shown that, in the process of interaction with the plasma, the laser pulse generates solitons propagating through the plasma layer and transferring the radiation through the opaque medium. The coefficient of transparency of the plasma layer for the soliton-like penetration of the laser radiation was calculated. The plasma parameters at which the collisionless absorption is small as compared to the transformation of the laser energy into solitons were found. 相似文献
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It is shown that the tight focusing of short ultraviolet laser pulses (248 nm, 450 fs) in the bulk of high bandgap transparent solids (fused silica) can result in structural modifications in the material. These can vary from small changes of the refractive index to birefringence, cracks and voids. This restructuring of the medium is due to the high laser intensities attained, and the plasma that is generated through multi-photon processes. The restructuring comes in the form of a string, which is the result of the nonlinear propagation of the laser beam in the medium as a self-trapped filament. We resume the conditions for the generation of the different types of modifications and comment on the temporal evolution and the role of the plasma strings at the trail of the light filaments. 相似文献