延迟双脉冲激光产生的空气等离子体的光谱研究

使用激光双光束方法，对激光大气等离子体的光谱进行了实验研究.由一台激光器产生的两束激光，其中一束用于产生等离子体(电离激光束)，另一束则用于对已产生的等离子体施加影响(作用激光束).作用激光束所引起的光谱特征变化的实验研究结果和相应的初步分析.结果表明，在作用激光束的影响下，激光大气等离子体光谱的强度在整体上都有明显的增加，而且，连续光谱的增强大于线状光谱；短波连续光谱的增强大于长波连续光谱；作用激光束相对于电离激光束的延时越大，谱线增强的相对值也越大；作用激光束对谱线的增强不存在明显的阈值效应.结果还表明，作用激光束除导致光谱幅度增强外，对激光大气等离子体中各种类谱线成分的衰变时间也有明显的影响：除个别谱线外，大多数谱线的衰变时间都有不同程度的延长.对结果的初步分析指出，上述结果是激光大气等离子体中的自由电子吸收作用激光束的能量后，在等离子体中有不同传递途径和不同传递效率的体现.该结果为深入了解激光大气等离子体衰变过程中的微观物理现象提供了新的线索，也为以延长激光大气等离子体衰变过程为目标的技术应用提供了实验依据. 关键词： 大气等离子体 双光束 等离子体光谱 谱线演化

Spectroscopic study on the air plasma induced by delayed dual laser pulses

By using a two laser beam method,the spectra of laser-induced air plasmas(LIAP)were studied experimentally.Two laser beams of a laser were used in the experiment.One of the beams was used to create the plasmas,which is called the ionizing-laser-beam(ILB),and the other beam was used to give influence to the plasmas,called action-laser-beam(ALB).This paper reports the experimental results and give a preliminary analysis of the modifications to the spectral characteristics due to the influence of the ALB.The experimental results indicated that the total spectral intensity of laser-induced air plasmas increased obviously under the action of the ALB.The increment of continuous spectra was greater than that of the line spectra;the increment of the short wavelength band was greater than that of the long wavelength band.The longer the delay-time of ALB behind the ILB,the larger the increase of spectra intensities.There is no threshold for the ALB to increase the laser-induced air plasmas spectral intensity.The results also showed that besides increasing the intensity,the decay-time for most of lines would increase under the influence of ALB.The preliminary analyses indicated that the results may be caused by electrons in the plasma which transfer their energy absorbed from the ALB via different routs with different efficiencies.These results provides some new sight into the microscopic mechanisms of the decay of laser-induced air plasmas,and also provides some experimental evidences for prolonging the decay-time of laser-induced air plasmas for some technical applications.