中文摘要：

报道在脉宽50fs-22ps，波长800nm脉冲激光作用下的空气电离阈值的研究结果，利用探测等离子体发光信号的方法，实验测量了激发空气电离所需的阈值激光强度。结果表明，当激光脉冲宽度从50fs增加到22ps时，阅值光强Ith从8.7×10^14W/cm^2下降到2．7×10^13W/cm^2；Ith经历了由迅速降低逐渐发展为缓慢降低的过程,在50fs-1ps和1ps-22ps的脉宽区间，分别利用基于多光子电离和多光子电离引发的碰撞电离的理论模型的计算结果和实验结果基本一致。

英文摘要：

The intensity thresholds of air ionization induced by 800 nm ultrashort laser pulses are investigated for laser pulse durations from 50 fs to 22 ps. The intensity threshold was determined by measuring the fluorescence energy of the stimulated air ionization plasma. It is shown that as the pulse duration increases from 50 fs to 22 ps, the threshold intensity of air ionization decreases from 8.7×10^14 to 2.7×10^13 W/cm^2 and undergoes the transition from rapid decrease to slow decrease. For pulse duration shorter than 1 ps, the theoretical calculation was done based on the muhiphoton ionization and for pulse duration longer than 1 ps, the calculation was done based on the impact ionization initiated by the muhiphoton ionization. For both above cases the calculated results are in good agreement with the experiment.