共查询到20条相似文献,搜索用时 796 毫秒
1.
利用皮秒和飞秒激光研究了激光在空气中聚焦产生单个等离子体通道的条件.研究发现,能量为8—12mJ皮秒激光被焦距为15cm的透镜聚焦后,可以产生较为稳定的单个通道.通过横向纵向阴影成像分析发现,通道的管壁对聚焦产生的自发光具有箍缩作用,而通道内部却有利于光的传输.同时还发现,当采用短焦距透镜时,能量低于10mJ的飞秒激光在空气中较易形成单个等离子通道.
关键词:
等离子体通道
皮秒激光
飞秒激光
阴影成像 相似文献
2.
3.
《光学学报》2010,(1)
理论上分析并从实验上验证了通过改变外加电场的频率来驱动的128×128元变焦液晶透镜阵列。将上电极设计为圆孔阵列,由于圆孔电极在单元区域内形成的非均匀电场分布,从而使液晶分子在不同位置处旋转角度不同,在液晶层内形成了折射率梯度分布,由此单元区域具有了光学聚焦特性。分析了由于外加电场频率改变引起液晶介电常数变化给液晶透镜阵列焦距带来的影响。实验中制作的液晶透镜阵列的焦距调节范围为20~600μm,焦点尺寸为10μm,响应时间为微秒量级,可以呈清晰的多重影像。通过使用外加电场的频率可以得到变焦液晶透镜阵列,降低了液晶透镜阵列的工作电压,提升了液晶透镜阵列工作响应速度。 相似文献
4.
5.
6.
7.
采用高功率抽运调Q激光器分别在真空和空气中烧蚀Ti-Al合金靶材激发等离子体,研究了在不同气体压强下透镜到靶材的距离对等离子体参数的影响机理对于焦距为111mm的聚焦透镜,当透镜到靶材距离小于透镜焦距时,随着距离逐渐接近焦距,真空和空气中电子温度、电子密度和谱线强度均逐渐增强.当透镜到靶材距离大于透镜焦距时,真空中,电子温度和电子密度仍然继续升高,而谱线强度却变化不大.空气中,等离子体参数却有不同的演化特性:等离子体的电子温度、电子密度和谱线强度在透镜到靶材距离为107 mm时达到最大值,当距离继续增大时,均呈现出迅速下降的趋势,当透镜到靶材距离大于112mm时,电子温度和电子密度又有明显上升,特征谱线强度却大幅下降. 相似文献
8.
从理论上研究部分相干光被一环形透镜聚焦,在焦点附近的轴上点的光强分布。研究结果表明,当部分相干光被一环形透镜聚焦时,最大聚焦光强不在几何焦点,而是位于透镜与几何焦点之间,出现焦移现象。并且,焦移量不仅依赖于透镜外半径的菲涅耳数,还依赖于部分相干光的空间相干度和中心拦截比。透镜的菲涅耳数越小,焦移越大;部分相干光的空间相干度越低,焦移越大。当菲涅耳数一定时,环形透镜的中心拦截比越大,焦移越大;当空间相干度很小时,情况就变得比较复杂。 相似文献
9.
激光多模式毛细管电泳检测器的光学设计及优化 总被引:2,自引:2,他引:0
提出一种基于毛细管电泳的激光多模式检测器.为设计并优化其光路构型,进行了理论分析和数学推导,并采用Matlab仿真,得到光路中各参量优化取值范围.在热透镜通道,激发光束腰半径越小,则热透镜效应越强.而探测激光束腰半径、束腰与样品距离、样品与探测面距离三个参量综合决定检出信号强度;在回射干涉通道,聚焦透镜焦距应较短,它与毛细管距离对检测影响很大,而与激光器、与探测面的两距离对检测影响相对较小;热透镜效应对回射干涉检测影响不明显,如要严格消除,可将两通道错开一适当距离. 相似文献
10.
受激布里渊散射相位共轭波的阈值性能 总被引:2,自引:0,他引:2
本文报道了在CCl_4液体中受激布里渊散射的阈值性能.研究了产生受激布里渊散射相位共轭波的阈值是随所用聚焦透镜的焦距,泵浦激光的脉宽和发散角等的变化而变化.实验表明,适当地增加聚焦透镜的焦距,即提高受激布里渊散射的阈值能量可以显著地消除受激布里渊散射与其它非线性效应的竞争. 相似文献
11.
This study aims to investigate the arc plasma shape and the spectral characteristics during the laser assisted pulsed arc welding process. The arc plasma shape was synchronously observed using a high speed camera, and the emission spectrum of plasma was obtained by spectrometer. The well-known Boltzmann plot method and Stark broadening were used to calculate the electron temperature and density respectively. The conductive mechanism of arc ignition in laser assisted arc hybrid welding was investigated, and it was found that the plasma current moved to the arc anode under the action of electric field. Thus, a significant parabolic channel was formed between the keyhole and the wire tip. This channel became the main method of energy transformation between the arc and the molten pool. The calculation results of plasma resistivity show that the laser plasma has low resistivity as the starting point of conductive channel formation. When the laser pulse duration increases, the intensity of the plasma radiation spectrum and the plasma electron density will increase, and the electron temperature will decrease. 相似文献
12.
Morrison P. J. Thompson W. B. Williamson P. R. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1978,6(4):435-441
Investigation of the current collected by a long wire in space has application to long antennas and the proposed space shuttle tethered subsatellite. Langmuir's result for current collection by a moving probe in a plasma is used to obtain expressions for the voltage and current as functions of position along a wire. Two cases are considered: firstly, one end of the wire is grounded to the plasma and secondly, the wire is allowed to assume a natural grounding point. Results are obtained as a function of the wire resistivity, length and diameter for various particle densities. Calculations for a 2mm diameter copper wire show that a current of 0.066 amperes of oxygen ions will be collected by a tether of 10 km in length. 相似文献
13.
Competition between multiphoton/tunnel ionization and filamentation induced by powerful femtosecond laser pulses in air 总被引:1,自引:0,他引:1
In this work we present experiments by focusing 42 femtosecond laser pulses in air using three differentfocal length lenses: f=100, 30 and 5 cm. For the longest focal length, only the filament, which is aweak plasma column,is observed. When the shorter focal length lens is used, a high density plasma isgenerated near the geometrical focus and coexists with a weak plasma channel of the filamemt. Under thetightest focusing condition, filamentation is prevented and only a strong plasma volume appears at tehgeometrical focus. 相似文献
14.
Experimental data for switching initiated by the electrical breakdown of air gaps up to 1.9 m long with an arbitrary geometry that are produced by an exploding copper wire 90 μm in diameter are presented. At an initial voltage of 11 kV, the stored energy equals 100–2100 J. Two channel formation conditions are possible: explosion of a wire without electrical breakdown and electrical breakdown in a channel produced by an exploding wire with a delay (current pause) no longer than 250 μs. Current and voltage waveforms across the discharge gap, as well as the resistivity values, under the electrical breakdown conditions are shown. Mechanisms and conditions for streamer initiation at a mean electric field strength in the discharge gap of 5.3–17.0 kV/m are discussed. The geometrical dimensions of plasma objects in the forming channel, the run of the electrical current under breakdown, and the formation mechanism of wire explosion products are found from color microphotographs. The formation mechanism of large aerosols in the form of tiny spherical copper and copper oxide (CuO, Cu2O) particles under wire explosion conditions is discussed. 相似文献
15.
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
16.
采用纳秒脉冲电源,在静止空气条件下,开展了不同气压、放电距离和电压条件下的大体积纳秒脉冲放电实验研究.研究表明,当长度固定为200mm时,气压为250Pa时,随着电压的增大,放电区域从圆锥电极附近扩展到整个通道.当电压为12kV时,放电布满整个通道;随气压升高,初始放电电压增大.实验中发现在电压升高到一定程度时纳秒脉冲电离出现不稳定性,表现在气压相对较低时等离子体出现径向波动,气压相对较高时非平衡等离子体放电向电弧放电转变.分析认为,为了实现大体积均匀放电等离子体的产生,阻止放电不稳定性发生,应该采用上升沿时间更短,脉宽更小,电压更高的纳秒脉冲电源. 相似文献
17.
《等离子体物理论文集》2017,57(1):20-28
A new ignition method of the spark gap based on plasma ejection is proposed in this paper, as the conventional trigatron spark gap performs poorly under the low working coefficient (the ratio of the charging voltage to the self‐breakdown voltage) in air. The plasma is generated by the capillary discharge, which has high pressure, high temperature and high velocity. The capillary discharge device is placed inside the low voltage electrode. As long as the triggering signal is sent to the device, a column of the plasma flow is ejected in axial direction and develops rapidly towards the high voltage electrode. Subsequently, the gap is broken down and a high resistive channel is formed, where the thermal ionization takes place and the arc across the whole gap is generated and develops into a well conductive channel. The process of the thermal ionization of the high resistive channel varies with the change of the spark gap distance. The breakdown delay and the delay jitter of the spark gap increase with the spark gap distance, as both parameters are mainly determined by the developing process of the plasma ejection. The characteristics of the plasma flow determine the possibility of the breakdown of the spark gap under the low working coefficient. The ignition method based on capillary plasma ejection has been proved by the preliminary experiments, which indicate that under the gap length of 8 cm and the working coefficient of less than 3%, the effective ignition is still achievable. 相似文献
18.
19.
20.
Kuniharu Takizawa 《Optics Communications》1981,37(5):345-348
One-dimensional focusing and optical modulation have been achieved using a Fresnel light modulator (FLM) based on a Fresnel lens consisting of Ti-diffused channel waveguides on LiNbO3. By this device, the height of diffraction pattern near the focal point is modulated with an applied voltage while the focusing effect is almost kept. The experimental results obtained from the FLM with 13 zones at 633 nm are as follows: the focal length is 12.4 cm, the full width of beam at half power 47 μm, the half-wave voltage 28 V, the extinction ratio 10.9 dB and the insertion loss 11.6 dB. 相似文献