Study On The Interactions Between The Laser Induced Plasma And Ambiance Backgrounds

Pulsed laser ablation (PLA) of a solid or liquid sample can produce transient plasma with super saturatation, high temperature, high degree of ionization and high-speed expansion. In this work the interactions between the PLA plasma and different ambience backgrounds were studied with the spectroscopic diagnostic method.Plasmas with high density, high purity, high ionization and low working pressure can be produced by electron cyclotron resonance (ECR) microwave discharge. If the PLA plasma was generated in the ambience of ECR plasma, there would be strong interactions between them as well as gas phase reactions occurring in the hybrid plasma. This process has been used as an innovative material synthesis method called electron cyclotron resonance plasma assisted pulsed laser deposition (ECR-PLD) by our group and utilized to fabricate some compound thin films. In this work, a pure Al target was ablated by the focused pulsed laser in low-working-pressure (about4*10-2Pa) backgrounds of pure N2gas and ECR nitrogen plasma and the emission lines of Al I, Al II, N2and N2+were investigated in detail. The optical emission spectroscopy (OES) measurement showed that under the influence of the PLA plasma, the temporal stability and the spatial homogeneity of ECR plasma were broken, and at the same time, its activity was promoted. On the other hand, the presence of ECR plasma as the ambiance background obviously prolonged the existence time of optical emission from the PLA plasma. The interactions between these two plasmas made themselves much more active, which also could be confirmed by the rise of nitrogen molecular ions’ vibrational and rotational temperature determined by fitting of the emission spectra.Laser-induced breakdown spectroscopy (LIBS) is a popular element analysis method for its flexibility, relatively lower costs, contactless analysis and the capability of detecting various elements simultaneously. To further improve its sensitivity, the enhancement of the laser induced plasma’s emission caused by the spatial confinement was investigated. In the air ambiance, when the block disk was located in front of the pure carbon target being ablated by a focused pulsed laser, the intensity enhancement of the spectra of CN molecules would take place in a time period and the rotational temperature of CN molecules would be increased correspondently. With increasing distance between the block disk and the target, the enhancement factor was decreased and the enhancement time period was delayed. The probe beam deflection (PBD) method was used to study the propagation of the shockwave which generated by the laser ablation of the target and reflected by the block disk. The results demonstrated the simultaneity of the moments when the reflected shockwave arrived and the emission enhancement of CN molecules occurred in a same region. Therefore, the cause of the emission enhancement could be inferred as that the reflected shockwave compressed and confined the plume and as a result the concentration of the excited CN molecules was increased. Meanwhile, the collision rate and the reaction rate in the plume were also increased thus more excited CN molecules were created. Hence, the emission intensity and rotational temperature of CN molecules was enhanced.