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1.
激光功率密度对Al膜靶后表面快电子发射的影响   总被引:2,自引:2,他引:0       下载免费PDF全文
 报道了在20 TW皮秒激光器上完成的p偏振激光与等离子体相互作用过程中产生的快电子的角分布和能谱测量结果。实验得到:当激光功率密度小于1017 W/cm2时,电子发射没有明显定向性,在激光入射面内多峰发射;当激光功率密度大于1017 W/cm2,小于1018 W/cm2时,电子主要沿靶面法线方向发射;当激光功率密度达到相对论强度时,电子主要沿激光传播方向发射;激光功率密度未达到相对论强度时,靶后表面法线方向快电子能谱拟合平均温度符合共振吸收温度定标率;激光功率密度达相对论强度以上时,靶后表面法线方向快电子能谱拟合平均温度高于已有的温度定标率。  相似文献   

2.
1.319μm连续YAG激光束对可见光面阵CCD系统的干扰研究   总被引:10,自引:6,他引:4       下载免费PDF全文
 利用1.319μm连续钇铝石榴石激光对可见光面阵CCD系统进行干扰实验,分析了该CCD系统发生干扰饱和的原因,计算了1.319μm激光辐照面阵可见光CCD的干扰饱和阈值,利用实验数据在定量上验证了计算结果。当像面上激光功率密度达到102W/cm2量级时,CCD出现饱和串音,达到102W/cm2量级时,出现全屏饱和。  相似文献   

3.
实验研究了CO2分子在飞秒强激光脉冲作用下的动力学过程,包括分子取向,隧穿电离和库仑爆炸,激光强度从1×1013W/cm2变化到6×1014W/cm2. 当激光强度小于分子的电离阈值时,CO2分子的非绝热转动激发形成一个相干转动波包,波包演化导致分子沿激光电场方向取向. 激光脉冲结束后,分子取向可以周期性地再现,利用另一束激光可以对取向结构进一步进行修饰. 当激光强度大于分子  相似文献   

4.
 研究了15 MW峰值功率脉冲激光与600 μm芯径石英光纤耦合中存在的空气击穿现象。对聚焦区域的空气击穿现象进行了理论和实验研究,测得空气击穿阈值为0.79×109 W/cm2。测得固体介质的激光损伤阈值为2.12×109 W/cm2,与理论计算结果相符。提出了七合一光纤耦合器用于解决空气击穿的办法,实验测得7根光纤并束的耦合效率为67.21%。结果表明光纤耦合器可有效解决15 MW峰值功率脉冲激光与600 μm芯径石英光纤的耦合。  相似文献   

5.
 利用脉冲Nd:YAG激光作用在铝、铜靶上,研究了不同入射激光能量下冲量耦合系数和离焦量之间的关系,以及不同功率密度情况下冲量耦合系数和光斑直径的关系。实验表明铝靶在入射激光脉冲能量由75.8 mJ增加到382.3 mJ时,冲量耦合系数峰值对应的最佳离焦量由-10 mm处远离焦点向透镜方向移到-18 mm,而对应的激光功率密度仅由2.0×109 W/cm2增加到3.9×109 W/cm2;铜靶实验规律和铝靶类似。等离子体屏蔽的吸收作用导致了冲量耦合系数达到最大值后迅速降低。铝靶在入射激光功率密度由0.7×109 W/cm2增大到1.0×1010W/cm2时,冲量耦合系数随光斑直径增大而增大,对应变化斜率由5.2×10-5N·s/(mm·J)增大到49.2×10-5N·s/(mm·J),表明了稀疏波对冲量耦合系数的削弱作用随入射激光功率密度增加而增加,随光斑直径增大而减小。  相似文献   

6.
利用侧向阴影照相技术探测靶的飞行速度   总被引:1,自引:0,他引:1       下载免费PDF全文
 建立起一套侧向阴影照相的光学系统,利用可见光作为探测光,在状态方程实验中对靶的飞行速度进行探测。在天光KrF准分子激光装置上进行激光打靶实验,激光波长为248.4 nm。在激光功率密度为8.3×1011 W/cm2的条件下,测得50 μm厚铝靶的飞行速度为3.28 km/s;在激光功率密度为4.7×101011 W/cm2的条件下,测得带100 μm厚烧蚀层的13 μm厚铝靶的飞行速度为2.52 km/s。最后进行了误差分析计算,实验中探测激光与靶表面偏离角度最大不会超过2.06°,偏离角对实验精度产生的影响可以被忽略。  相似文献   

7.
陈荣  温彩霞 《光子学报》1998,27(1):56-59
分别采用功率密度为1.7W/cm2、照射剂量为2000J/cm2的Ar+激光与LD激光辐照高耐药性的志贺氏福氏痢疾杆菌,波长较短的Ar+激光(488nm)所引起细菌的致死率与药敏实变率明显高于波长较长的LD激光(808nm),即波长较短的Ar+激光的辐照导致细菌耐药性显著降低.  相似文献   

8.
段国平  陈俊领  韩俊鹤  黄明举 《光子学报》2014,40(11):1657-1661
利用等离子增强化学气相沉积系统制备了本征非晶硅薄膜,并选用488 nm波长的连续激光进行晶化.采用喇曼测试技术对本征非晶硅薄膜在不同激光功率密度和扫描时间下的晶化状态进行了表征,并用514 nm波长与488 nm波长对样品的晶化效果进行了比较.测试结果显示:激光照射时间60 s, 激光功率密度在1.57×105 W/cm2时,能实现非晶硅向多晶硅的转变,在功率密度达到2.7 56×105 W/cm2时,有非晶开始向单晶转变,随着激光功率密度的继续增加,晶化结果仍为单晶;在功率密度为2.362×105 W/cm2下,60 s照射时间晶化效果较好;在功率密度为2.756×105 W/cm2和照射时间为60 s的条件下,用488 nm波长比514 nm波长的激光晶化本征非晶硅薄膜效果较好,并均为单晶态.  相似文献   

9.
报道在脉宽50fs—22ps,波长800nm脉冲激光作用下的空气电离阈值的研究结果.利用探测等离子体发光信号的方法,实验测量了激发空气电离所需的阈值激光强度.结果表明,当激光脉冲宽度从50fs增加到22ps时,阈值光强Ith从8.7×1014W/cm2下降到2.7×1013W/cm2Ith经历了由迅速降低逐渐发展为缓慢降低的过程.在50fs—1p  相似文献   

10.
 报道COIL激光用变形反射镜的介质反射多层膜实验。在真空镀膜机内制备了膜系Sub/Ag(SiO2/HfO2)4/air和Sub/Ag(YbF3/ZnS)3/air, 反射率分别为99.90%和99.87%。在经历109次循环后变形镜物理特性无变化。研究了COIL激光辐射下热畸变和损伤特性。分别在功率密度为1.52kW/cm2和1.18kW/cm2的COIL激光辐照下,这两种膜系的变形镜波前变化为0.37l 和0.54l 。因此对于变形镜1kW/cm2激光功率密度是安全可靠的。  相似文献   

11.
A study of Ti laser irradiation and thin film deposition produced by an Nd:Yag pulsed laser is presented. The laser pulse, 9?ns width, has a power density of the order of 1010?W/cm2. The titanium etching rate is of the order of 1?µg/pulse, it increases with the laser fluence and shows a threshold value at about 30?J/cm2 laser fluence. The angular distribution of ejected atoms (neutrals and ions) is peaked along the normal of the target surface. At high fluence, the fractional ionization of the plasma produced by the laser is of the order of 10%. Time-of-flight measurements demonstrate that the titanium ions, at high laser fluence, may reach kinetic energies of about 1?keV. Obtained results can be employed to produce energetic titanium ions, to produce coverage of thin films of titanium and to realize high adherent titanium-substrate interfaces. The obtained results can be employed to produce energetic titanium ions, to produce a coverage of thin titanium films on polymers, and to realize highly adherent titanium–substrate interfaces.  相似文献   

12.
It is well known that a crater is formed on the target surface by the irradiation of intense laser pulses in laser ablation. In this work, we report that additional pits are formed on the bottom surface of the ablation crater due to the collapse of a cavitation bubble in liquid-phase laser ablation. We observed the formation of several cavitation-induced pits when the fluence of the laser pulse used for ablation was approximately 5 J/cm2. The number of cavitation-induced pits decreased with the laser fluence, and we observed one or two cavitation-induced pits when the laser fluence was higher than 10 J/cm2. In addition, we examined the influence of the liquid temperature on the formation of cavitation-induced pits. The collapse of the cavitation bubble was not observed when the liquid temperature was close to the boiling temperature, and in this case, we found no cavitation-induced pits on the bottom surface of the ablation crater. This experimental result was discussed by considering the cavitation parameter.  相似文献   

13.
利用波长为800 nm的飞秒激光,在空气和去离子水中诱导钛表面形成不同的周期条纹结构。在空气中,激光能量密度为0.265 J/cm2时,钛表面主要形成周期为500~560 nm低空间频率条纹结构;激光能量密度为0.102 J/cm2时,主要形成的是周期为220~340 nm高空间频率条纹结构。两种条纹均垂直于入射激光偏振方向,且条纹周期随着脉冲重叠数的增大而增大。在水中,除形成垂直激光偏振方向、周期为215~250 nm的高空间频率条纹结构,还形成了平行于激光偏振方向且周期约为入射激光波长八分之一的高空间频率条纹结构。利用表面等离子体理论、二次谐波及Sipe理论对各种周期条纹结构的形成机理进行分析,发现周期条纹结构的形成与钛表面氧化层有密切的关系。  相似文献   

14.
This work considers the propagation of light in a semitransparent layer of vascular tissue, submitted to radiative boundary conditions. The solution procedure must provide accurate light distribution in the layer, so a discrete ordinates method based on the exact transport theory is carried out. An advantage of this method is its ability to account easily for various boundary conditions as well as optical heterogeneity. The influences of anisotropic scattering, optical discontinuity, optical parameters of tissue and refractive index on radiant fluence rate are investigated carefully. It is shown that reflections tend to produce more uniform profiles within the tissue.  相似文献   

15.
A collinear irradiation system of F2 and KrF excimer lasers for high-quality and high-efficiency ablation of hard materials by the F2 and KrF excimer lasers’ multi-wavelength excitation process has been developed. This system achieves well-defined micropatterning of fused silica with little thermal influence and little debris deposition. In addition, the dependence of ablation rate on various conditions such as laser fluence, irradiation timing of each laser beam, and pulse number is examined to investigate the role of the F2 laser in this process. The multi-wavelength excitation effect is strongly affected by the irradiation timing, and an extremely high ablation rate of over 30 nm/pulse is obtained between -10 ns and 10 ns of the delay time of F2 laser irradiation. The KrF excimer laser ablation threshold decreases and its effective absorption coefficient increases with increasing F2 laser fluence. Moreover, the ablation rate shows a linear increase with the logarithm of KrF excimer laser fluence when the F2 laser is simultaneously irradiated, while single KrF excimer laser ablation shows a nonlinear increase. The ablation mechanism is discussed based on these results. Received: 16 July 2001 / Accepted: 27 July 2001 / Published online: 2 October 2001  相似文献   

16.

A pulsed infrared laser (Q-switched Nd:Yag) is employed to irradiate different metal targets having atomic number from Z =13 up to Z =82. The high laser fluence deposited on the metals, of the order of 100 v J/cm, produces high ablation yield and a plasma generation at the target surface. The emitted species are neutral and ionized atoms. Both components have been investigated in terms of yield emission, time-of-flight measurements and angular distribution. Results indicate that the main emission occurs mainly along the normal to the target surface, that the etching, at high fluence, is of the order of 10 v atoms/ pulse, that the atoms velocities are of the order of 10 v m/s, that the maximum ion energies are of the order of keV. During the laser irradiation, expanding and non-equilibrium plasma is produced in front of the target. The plasma has a fraction ionization depending by the metal species and generally within 10% and 80%. The plasma'temperature, at high fluence, can be theoretically calculated and reaches about 10 v K. The fractional ionization of the plasma, experimentally measured, has been investigated as a function of the laser fluence and of the energy binding of the target molecules. The ion emission yield is presented and discussed in view of the possibility to realize a laser ion source for ion accelerators.  相似文献   

17.
Oxygen and nitrogen insertion in a titanium substrate is performed in air using a Q-switched Nd-YAG laser. This process modifies the surface by the formation of specific layers on the substrate. These layers show different properties, largely influenced by the insertion of elements in the layers. The treatment conditions, especially the laser parameters (fluence and repetition rate), must be known and controlled. Using nuclear analysis, we demonstrate that oxygen insertion is mainly influenced by repetition rate, and that nitrogen insertion is controlled by laser fluence. The physical phenomena involved in the oxygen and nitrogen insertion are discussed.  相似文献   

18.
Femtosecond laser micromaching silicon is investigated by a Ti:sapphire laser (800 nm, 1 kHz) with a pulse duration of 130 fs. It is investigated that the result is affected by fluences at a different number of pulse. In the experiment, we have observed the periodic surface structure such as microholes, and found that the direction of the array holes was parallel to the laser polarization direction. This result has potential application in the fabrication of two-dimensional photonic crystals. We have determined the optimal conditions for producing these surface structures. At the same time, when we change the fluence and the pulse number, the ripples and the columns emerge. If the pulse number remains unchanged, we also investigated the evolution of a crater at a different pulse fluence. The microholes will become regular cracks on the outer irradiation area, and the ripples will gradually disappear. But, the column structures will appear. At a higher fluence, ripples only appear when the number of pulses (N) is less than 200 and a column structure exists at the center region when N is above 600.  相似文献   

19.
以1064 nm波长作用下的HfO2/SiO2高反射薄膜为研究对象,研究了高反射薄膜在损伤生长过程中分层剥落初始损伤结构的变化规律、损伤形貌特征和损伤生长阈值等特性。实验结果表明:分层剥落初始损伤结构的横向尺寸随激光能量密度的增加呈分段线性增长,破斑沿纵向拓展的损伤生长阈值是沿横向拓展的损伤生长阈值的2倍以上,初始损伤结构横向尺寸的生长率与能量密度呈指数关系,且生长阈值随着辐照次数的增加显著降低。  相似文献   

20.
A thermal model to describe the high-power nanosecond pulsed laser ablation is presented. It involves the vaporization and the following plasma shielding effect on the whole ablation process. As an example of Si target, we obtainthe time evolution of the calculated surface temperature, ablation rate and ablation depth. It can be seen that plasma shielding plays a more important role in the ablation process with time. At the same time, the ablation depth with laser fluence based on different models is shown. Moreover, we simulate the pulsed laser irradiation Ni target. The evolution of the transmitted intensity and the variation of ablation depth per pulse with laser fluence are performed. Under the same experimental conditions, the numerical results calculated with our thermal model are more in agreement with the experimental data.  相似文献   

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