共查询到20条相似文献,搜索用时 343 毫秒
1.
2.
采用紧聚焦的超强短脉冲激光与固体通道靶相互作用是获得大电量、高准直相对论电子束的一种有效方式。实验中由于激光预脉冲烧蚀靶壁产生预等离子体会膨胀、填充到真空通道中,从而导致电子束品质发生变化。采用二维PIC粒子模拟程序研究了通道靶中填充预等离子体的电子加速过程。模拟结果显示,在功率密度为5.0×10^(20W/cm^(2))的超强短脉冲激光条件下,通道中填充一定密度的等离子体时激光场优先与低密度等离子体相互作用,激光脉冲与通道壁的相互作用减弱,电子加速机制由纵向场主导的真空电子加速转变为横向电场主导的等离子体电子加速,产生电子束具有更大的电荷量,但能量降低,发散角增大。 相似文献
3.
4.
������������Ƶ�����ܼ�Ramanɢ�������Ƿֲ����� 总被引:1,自引:1,他引:0
介绍了在神光Ⅱ装置上开展的长脉冲2ns三倍频激光与黑腔靶相互作用的实验。报道了采用PIN探测器阵列测量大角度受激Raman散射(SRS)角分布和采用激光卡计对背向SRS光能量积分测量的实验结果。相同实验条件下激光辐照缝靶产生的SRS光能量要强于激光与全腔靶作用产生的SRS光,小腔靶的SRS光能量要强于标准腔靶。对比长脉冲2ns及短脉冲1ns激光打靶实验结果可以看出:由于激光功率密度的下降,长脉冲激光打靶时SRS散射光能量要弱于短脉冲激光打靶。长脉冲2ns激光与标准腔靶相互作用时,等离子体堵腔比较严重。 相似文献
5.
采用二维雷诺平均N-S方程,数值模拟研究了大气条件下短脉冲激光与固体靶相互作用所产生等离子体的动力学过程。采用k-ε两方程模型用于湍流的数值模拟,分别利用ROE格式和二阶中心格式对对流通量和粘性通量进行离散处理;用高斯-赛德尔隐式格式对方程进行时间推进求解。数值模拟给出了激光引发靶蒸气等离子体侧向膨胀、稀疏等二维流体动力学过程的物理图像,讨论了靶与光斑尺寸对脉冲激光冲量的影响。结果表明,不同宽度固体靶受到的激光冲量有很大差异,固体靶宽度越大,受到的激光冲量也越大。 相似文献
6.
激光与固体靶面烧蚀等离子体的能量耦合计算 总被引:1,自引:0,他引:1
强激光辐照下固体靶表面迅速汽化产生靶蒸气等离子体,激光穿过等离子体区到达固体靶表面的过程就是激光束与等离子体的能量耦合与交换过程。采用具有五阶精度的WENO差分格式和简易等离子体状态方程模型对激光与等离子体相互作用的复杂物理过程进行了数值计算,分析了激光束能量在等离子体区中的吸收、屏蔽效应等动态耦合规律以及激光支持等离子体前驱冲击波传播。数值模拟结果表明:激光能量是支持靶面等离子体运动的唯一原因,能量屏蔽效应对激光与等离子体能量耦合有很大影响,通过控制激光脉冲宽度,可以合理调节屏蔽效应的影响。 相似文献
7.
8.
超短超强激光与固体靶表面等离子体相互作用可以通过高次谐波的方式产生从极紫外到软X射线波段的相干辐射,获得飞秒甚至阿秒量级的超短脉冲,可用于观测原子或分子中的电子运动等超快动力学过程.本文实验研究了相对论圆偏振飞秒激光与固体靶相互作用的高次谐波产生过程,实验结果表明,在较大入射角下,圆偏振激光也可以有效地产生高次谐波辐射.通过预脉冲控制靶表面的预等离子体密度标长,发现高次谐波的产生效率随密度标长的增加而单调下降.进一步通过二维粒子模拟程序,分析了激光的偏振以及预等离子体密度标长对高次谐波产生的影响,很好地解释了实验观测结果. 相似文献
9.
10.
11.
12.
Characteristic investigation of ablative laser propulsion driven by nanosecond laser pulses 总被引:1,自引:0,他引:1
Z.Y. Zheng J. Zhang X. Lu Z.Q. Hao X.H. Yuan Z.H. Wang Z.Y. Wei 《Applied Physics A: Materials Science & Processing》2006,83(2):329-332
The momentum transfer and the specific impulse of the ablative laser propulsion of nanosecond laser irradiation on copper,
lead, aluminum and graphite targets are investigated. The effects of the ambient pressure and laser focal spot sizes on the
target momentum are measured. The results show that the target momentum strongly relates to the ambient pressure and target
property. The highest target momentum about 2.28 g·cm/s is obtained on lead targets under 1 atmospheric pressure. With the
increase of the focal spot sizes, the specific impulse decreases. The highest specific impulse in vacuum is about 950 s on
copper targets.
PACS 52.75.Di; 52.38.Mf; 52.50.Jm 相似文献
13.
14.
A high power pulse Nd-glass laser system with plasma mirror is studied. Plasma is created on the surface of a solid target and the action is superradiantly triggered. Long trains of modelocked pulses are generated if the carbon or metal targets are used and Q-switched pulses are observed with dielectric targets like PVC. Tens of joules of light energy are extracted from the laser medium and absorbed by plasma in both regimes. Spatial and temporal structures of the laser beam are very reproducible, the laser action is insensitive to variations in air pressure inside the target chamber. Stimulated Brillouin back-scattering in the underdense plasma is discussed as the nonlinear mechanism governing the plasma reflectivity. 相似文献
15.
Thomas Lehecka Andrew Mostovych Jeffrey Thomas 《Applied Physics A: Materials Science & Processing》2008,92(3):727-741
Time resolved emission from the interaction of ultra-short (∼200 fs) laser pulses with aluminum and copper targets was investigated.
Measurements show that emission from the laser produced plasma in air is significantly more intense than in near vacuum conditions
and that the emission in air can extend for periods exceeding 100 ns. Modeling the laser–target–air coupling shows that the
laser–target interaction can lead to blast wave shock waves being launched in the ambient air and that the emission from the
shocked air dominates over emission from the target surface. The long term emission measurements in air are in agreement with
the modeling results. 相似文献
16.
The coupling of visible nanosecond laser pulses to metallic targets irradiated in vacuum is studied. The expressions of the vapour and plasma ignition times are obtained. Two cases for vapour breakdown in the plasma ignition process are considered. The first case is that 40 generations of new electrons are born in vapour generation time before plasma formation as assumed in the literature. The second case is that 10 generations of new electrons are born in vapour generation time. Molybdenum (Mo), niobium (Nb) and aluminium (Al) targets are considered for illustrations of our results. The expression of the plasma ignition time for the Al target is substantially different from that reported in the literature. The vapour and plasma ignition threshold laser intensities are calculated and compared with those reported in the literature. Reasons for disagreement are discussed. The plasma ignition threshold estimated in the second case is noted to be in good agreement with the reported experimental result. 相似文献
17.
The optimum parameters for laser propulsion are discussed, such as laser induced pressure on targets, interaction parameters (Cm, Isp) and optimum laser intensity Is, etc. It is verified that the larger laser power density will induce higher thrusting force. It is also found that, to drive a 1.010-kg target during confined laser ablation in vacuum and a 17.45-g one during direct laser ablation in air at the standard pressure, the needed minimum power intensities are on the same order of magnitude. 相似文献
18.
Recently the dynamically assisted Schwinger mechanism, i.e., electron–positron pair production from vacuum by a combination of laser pulses with different time scales has been proposed. The corresponding results, which suggest that the rate of produced pairs is significantly enhanced by dynamical effects, are verified. Employing the framework of quantum kinetic theory intrinsically enables us to additionally provide momentum space information on the generated positron spectrum. 相似文献
19.
The interaction of femtosecond laser pulses with solid targets was studied through experiments and particle-in-cell (PIC) simulations. It is proved that the vacuum heating and the inverse bremsstralung process are the main mechanisms of the laser pulse absorption under such conditions. The distribution of hot electrons and that of X-ray are found to have double-temperature structure, which is confirmed by PIC simulations. While the lower temperature is attributed to the resonant absorption, the higher one, however, is caused by the laser-induced electric field in the target normal direction. The time-integrated spectra ofthe reflected laser pulse shows that the mechanism of electron acceleration is determined by the plasma density profile. 相似文献
20.
Thrust enhancement via gel-type liquid confinement of laser ablation of solid metal propellant 总被引:1,自引:0,他引:1
Soojin Choi Tae-hee Han Ardian B. Gojani Jack J. Yoh 《Applied Physics A: Materials Science & Processing》2010,98(1):147-151
Laser propulsion has been developed as a suitable small thruster technology for the attitude control of micro and nano class
satellites. Laser-based thrusters meet the satellite design criteria for being of light weight and cost effective, because
they do not require fuel storing and oxidizer for combustion. Also, thrust control by laser propulsion is achieved fairly
easy. In this paper, we consider the confinement of plasma expansion by a gel-type liquid material, which results in the enhancement
of the thrust for propulsion. We also present our attempts to resolve some known issues regarding laser ablation of solid
and liquid targets. The level of thrust is quantified via the momentum coupling coefficient, which was experimentally measured
using a ballistic pendulum system. We have discovered that the laser ablation confinement by the gel-type medium results in
2.3 times more enhanced driving force as compared to the water confinement. A proof of performance is demonstrated for using
gel-type material for generating propulsion, and material characterization for optimal thrust performance is presented. 相似文献