中文摘要：

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107mm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．

英文摘要：

The analysis of nanosecond laser-induced plasma versus the lens-to sample distance（LTSD） is investigated by 532nm laser ablated Ti-A1 alloys in air and vacuum condition. The results indicate that electron temperature and density increase rapidly with the LTSD changing from short distance to the focal length （f=111 mm）. Moreover, the plasma parameters by laser ablation in vacuum condition will further increase with LTSD further increasing. As for ambient medium, the plasma parameters reach their maximum values at 107 mm and then substantially decrease. On the other hand, the electron temperature and density rise again, while the intensity of Ti（Ⅱ）368.52 nm decreases rapidly when the LTSD extends 112 mm.