排序方式: 共有44条查询结果,搜索用时 31 毫秒
31.
Intense supercontinuum generation in the near-ultraviolet range from a 400-nm femtosecond laser filament array in fused silica 下载免费PDF全文
An intense supercontinuum(SC) in the near-ultraviolet range is generated from filamentation by focusing a 400-nm laser into fused silica with a microlens array(MLA). The spectrum of the SC is shown to be sensitive to the distance between the MLA and fused silica. In our optimal conditions, the near-ultraviolet SC can cover a range of 350-600 nm,where a bandwidth of approximately 55 nm above the 1μJ/nm spectral energy density and 20 nm bandwidth with tens ofμJ/nm are achieved. In addition, the energy conversion efficiency of the 400 nm laser for SC generation is further analyzed.A maximum conversion efficiency of 66% is obtained when the entrance face of fused silica is set around the focus of the MLA. 相似文献
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Shadowgraph investigation of plasma shock wave evolution from Al target under 355-nm laser ablation 下载免费PDF全文
The propagation of a plasma shock wave generated from an Al target surface ablated by a nanosecond Nd:YAG laser operating at 355 nm in air is investigated at the different focusing positions of the laser beam by using a time-resolved shadowgraph imaging technique. The results show that in the case of a target surface set at the off-focus position, the condition of the focal point behind or in front of the target surface greatly influences the evolution of an Al plasma shock wave, and an ionization channel forms in the case of the focal point set in front of the target surface. Moreover, it is found that the shadowgraph with the evolution time around 100 ns shows that a protrusion appears at the front tip of the shock wave if the focal point is at the target surface. In addition, the calculated results of the expanding velocity of the shock wave front, the mass density, and pressure just behind the shock wave front are presented based on the shadowgraphs. 相似文献
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利用激光诱导击穿光谱技术结合机器学习算法,对东北5个产地(大兴安岭、集安、恒仁、石柱、抚松)的人参进行产地识别,建立了主成分分析算法分别结合反向传播(BP)神经网络和支持向量机算法的人参产地识别模型.实验采集了5个产地人参共657组在200-975 nm的激光诱导击穿光谱,经光谱数据预处理后,对C,Mg,Ca,Fe,H,N,O等元素的8条特征谱线进行主成分分析,原光谱数据的前3个主成分累积贡献率达到92.50%,且样品在主成分空间中呈现良好的聚集分类.降维后的前3个主成分以2∶1进行随机抽取,分别作为分类算法的训练集和测试集.实验结果表明主成分分析结合BP神经网络及支持向量机的平均识别率分别为99.08%和99.5%.发生误判的原因是集安和石柱两地地理环境的接近而导致的H,O两元素在Ca元素离子发射谱线下的归一化强度相似.本研究为激光诱导击穿光谱技术在人参产地的快速识别提供了方法和参考. 相似文献
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超短脉冲强激光在空气中传输时由于非线性克尔自聚焦效应会使激光光束聚焦,造成空气的离化而形成等离子体,等离子体对激光光束又会产生散焦作用,这两种过程的动态平衡可以形成很长的等离子体通道,从而产生一系列复杂而有趣的现象.文章对通道形成的机理、锥角辐射、超连续谱和三次谐波的产生进行了阐述,并介绍了目前等离子体通道形成的几种理论模型.文章还对通道内的各种复合和辐射机制进行了分析. 相似文献
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基于正交预烧蚀双脉冲激光诱导击穿光谱(DP-LIBS) 技术对长春市四个地点地表土壤样品中的重金属元素进行了研究, 根据光谱线强度定性分析了重金属元素Mn, Cr, Cu, Pb含量.实验结果发现, 在532和1064 nm激光脉冲能量分别为70和100 mJ的条件下光谱增强随延时的变化出现双峰结构. 脉冲间延时20 μs时, Mn I 406.4 nm光谱增强幅度达到2.75倍, 延时为30 μs时出现第二个尖峰, 增强幅度为2.4倍.最后对正交预烧蚀DP-LIBS光谱增强机理进行了讨论.
关键词:
预烧蚀
双脉冲激光诱导击穿光谱
光谱增强
土壤污染 相似文献
36.
强激光与固体靶相互作用时,产生的高速喷射的等离子体对靶具有强烈的反冲作用,因此,激光等离子体可以作为一种新型的推进动力源.与传统的化学燃料推动相比,激光等离子体具有较高的比冲和有效载荷比等特点.对纳秒激光脉冲与铝、石墨、铅和碳氢靶相互作用时,等离子体对靶的冲量进行了实验测量,研究了大气与真空环境下的靶动量与激光聚焦面积的关系,并对部分实验结果与理论计算的数值进行了比较.实验结果显示,大气与真空环境下的靶动量有很大的差异,并且真空下的靶动量受材料性质的影响较大,与以往长脉冲激光的实验结果有很大的不同.
关键词:
激光等离子体
动量
动量耦合系数 相似文献
37.
Acoustic Diagnostics of Plasma Channels Induced by Intense Femtosecond Laser Pulses in Air 总被引:4,自引:0,他引:4 下载免费PDF全文
Long plasma channels induced by femtosecond laser pulses in air are diagnosed using the sonographic method. By detecting the sound signals along the channels, the length and the electron density of the channels are measured. Refocusing is also observed at different laser energies and different focal lengths. We find that the sonographic method has manifest advantages compared to other techniques. 相似文献
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We investigate the effects of confined laser ablation on laser plasma propulsion. Compared with planar ablation, the cavity ablation provides an effective way to obtain a large target momentum and a high coupling coefficient. When laser pulses are focused into a cavity with 1 mm diameter and 2ram depth, a high coupling coefficient is obtained. By using a glass layer to cover the cavity, the coupling coefficient is enhanced by 10 times. Meanwhile, it is found that with the increase of the target surface size, the target momentum presents a linear increase. 相似文献
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