为了探究飞秒激光成丝的内在机制以实现长度表征, 采用荧光法和声学法, 得到了不同入射激光脉冲能量下和偏振态下等离子体光丝的荧光光谱和声音信号信息。结果表明,在相同激光脉冲能量下圆偏振光产生的N2荧光信号强度约为线偏振光的2倍, 而线偏振光产生的N2+荧光信号强度则约为圆偏振光的1.3倍; 等离子体荧光测量是获取等离子体光丝长度的有效途径, 相比于声学测量法更精确。该研究为揭示相干激光发射随光丝长度变化的物理实质提供了光丝长度表征的可行方案。

To investigate the intrinsic mechanism of femtosecond laser filament formation to achieve length characterization, fluorescence spectra and acoustic signal information of the plasma filament at different incident laser pulse energies and polarization states were obtained by fluorescence and acoustic methods. The results show that, the intensity of N2 fluorescence signal produced by circularly polarized light is about twice of that of linearly polarized light with the same laser pulse energy, while the intensity of N2+ fluorescence signal produced by linearly polarized light is about 1.3 times of that of circularly polarized light; Plasma fluorescence measurement is an effective way to obtain the length of plasma filament, which is more accurate than acoustic measurement. This study provides a feasible solution to characterize the filament length by revealing the physical essence of coherent laser emission with filament length.