研究了脉冲能量对飞秒激光等离子体丝形成的影响, 基于荧光光谱法和照相图像法得到脉冲能量对飞秒激光等离子体丝长度和成丝起点的影响规律。实验结果表明：飞秒激光在大气中传输时, 经透镜聚焦后形成较长的等离子体丝; 随着脉冲能量的增大, 等离子体丝的成丝起点位置向聚焦透镜位置移动, 同时等离子体丝的长度增加; 等离子体丝辐射的N2 337 nm荧光谱线强度峰值位置靠近聚焦透镜, 并且整体荧光光谱强度得到增强; 相比于照相图像法, 荧光光谱法测量得到的等离子体丝长度更加可靠。最后对脉冲能量对等离子体丝起点位置的影响进行了理论解释。

The effect of pulse energy on the formation of femtosecond laser plasma filament is studied by the fluorescence spectrum method and the photographic imaging method, and the influence of pulse energy on the length and the starting position of femtosecond laser plasma filament is obtained. The experimental results show that the long plasma filament forms after focusing of lens when the femtosecond laser transmits in the air. As the laser energy is increasing, the starting position of plasma filament moves toward the position of the focusing lens and the plasma filament length increases. The position of the peak intensity of the N2 337 nm fluorescence spectrum is close to the focusing lens, and the whole fluorescence spectrum intensity increases. Compared with the photographic imaging method, the fluorescence spectrum method has high reliability in the plasma filament length measurement. Finally, the influence of pulse energy on the starting position and the length of plasma filament is explained theoretically.