飞秒激光激发空气电离的阈值研究

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，阈值光强I_th从8.7×10¹⁴W/cm²下降到2.7×10¹³W/cm²；I_th经历了由迅速降低逐渐发展为缓慢降低的过程.在50fs—1p关键词：飞秒激光阈值多光子电离碰撞电离

Determination of air ionization threshold with femtosecond laser pulses

The intensity thresholds of air ionization induced by 800nm ultrashort laser pulses are investigated for laser pulse durations from 50fs to 22ps. 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 50fs to 22ps, the threshold intensity of air ionization decreases from 8.7×10¹⁴ to 2.7×10¹³W/cm² and undergoes the transition from rapid decrease to slow decrease. For pulse duration shorter than 1ps, the theoretical calculation was done based on the multiphoton ionization and for pulse duration longer than 1ps, the calculation was done based on the impact ionization initiated by the multiphoton ionization. For both above cases the calculated results are in good agreement with the experiment.