In this study, a femtosecond laser was focused to ablate brass target and generate plasma emission in air. The influence of lens to sample distance (LTSD) on spectral emission of brass plasma under linearly and circularly polarized pulses with different pulse energies was investigated. The results indicated that the position with the strongest spectral emission moved toward focusing lens with increasing the energy. At the same laser energy, the line emission under circularly polarized pulse was stronger compared with linearly polarized pulse for different LTSDs. Next, electron temperature and density of the plasma were obtained with Cu (I) lines, indicating that the electron temperature and density under circularly polarized pulse were higher compared to that under linearly polarized pulse. Therefore, changing the laser polarization is a simple and effective way to improve the spectral emission intensity of femtosecond laser-induced plasma.

在这项研究中，飞秒激光聚焦烧蚀黄铜靶并在空气中产生等离子体发射。研究了不同脉冲能量的线性和圆偏振脉冲下透镜到样品距离（LTSD）对黄铜等离子体光谱发射的影响。结果表明，随着能量的增加，光谱发射最强的位置向聚焦透镜移动。在相同的激光能量下，对于不同的LTSD，圆偏振脉冲下的线发射比线偏振脉冲更强。接下来，用Cu（I）线获得等离子体的电子温度和密度，表明圆极化脉冲下的电子温度和密度高于线极化脉冲下的电子温度和密度。所以，