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.