激光大气等离子体时间演化特性的光谱研究

Spectroscopic Study on the Time Evolution Behaviors of the Laser-induced Air Plasma

采用延时光谱法和谱线演化法 ,对YAG脉冲激光器 1 0 6 μm光束击穿一个大气压的空气所产生的等离子体进行了时间分辨光谱研究。对激光大气等离子体连续光谱的短波带与长波带分别进行了时间分辨测量 ,结果表明两者的衰变速率均在等离子体激发约 0 5微秒以后明显变慢。分析认为这种衰变速率的变慢可能与空气中氧对自由电子的吸附与去吸附有关。对激光大气等离子体线状光谱所作的时间分辨测量则表明 ,大部分线状光谱的演化寿命大于其标称寿命 ,部分线状光谱还呈现“衰变—增涨—衰变”的复杂形式。分析认为线状光谱的这些演化特征可能与等离子体在衰变期间的各种复合过程和能量转移过程有关。

The time-resolved spectra of the air-breakdown plasma produced by the 1.06 mum beam of a Nd: YAG laser were investigated by using the time-delayed spectra and the spectral line evolution methods. The time evolutions of the short wavelength band and long wavelength band of the continuous spectra of the air-breakdown plasma have been measured. The result shows that the decay rates of both bands are slowing down 0.5 mus after the excitation of the plasma, and the attachment and the detachment of free electrons by Q in the plasma could be the reason for this behavior. The results of the time-resolved measurements of the line spectra show that most of the line spectra have the evolution time longer than their lifetimes, and the evolutions of some line spectra take a fashion of 'decay-grow-decay'. We consider these evolution behaviors of the line spectra to be related to various recombination processes and the energy transfer processes of the decaying plasma.