为研究飞秒激光超短脉冲序列在空气中传输的时间相干特性，根据飞秒脉冲序列的传播理论和空气折射率Ciddor公式，建立了飞秒激光脉冲序列间脉冲在空气中传播的互相关数值模型。根据该模型可以得到不同光谱分布、不同光程差和不同大气条件下的飞秒脉冲序列间脉冲的互相关图形。数值模拟结果表明随着脉冲间光程差的增大，由于色散的原因，互相关图形加宽和啁啾，并且峰能量减小；然而当光程差不变，仅改变大气条件时，互相关图形仅仅作线性移动，没有任何额外线性加宽或啁啾。飞秒光学频率梳具有非常高的时间相干性，并且飞秒脉冲间的互相关图形只取决于激光器光源的光谱分布。

The numerical model of the cross-correlation between pulses of the femtosecond laser sequence propagating in air is developed to investigate the temporal coherence characteristic of the femtosecond laser ultrashort pulse sequence. The model is based on the propagation theory of the femtosecond pulse sequence and the refractive index of air Ciddor formula. The auto-correlation patterns between pulses of the femtosecond pulse sequence in different spectral distribution with different optical path differences under different atmospheric conditions can be obtained from the model. The simulation results show that the auto-correlation patterns become broadening and chirp with the peak power decreasing due to dispersion, as the optical path difference between the pulses increases. However when the atmospheric conditions are changed with the same optical path difference, the correlations patterns only shift without any extra linear broadening or chirp. The femtosecond optical frequency comb has very high temporal coherence. The formation of the cross-correlation function between the femtosecond pulses only depends on the spectral distribution of the laser source.