中文摘要：

理论研究了当基频光（ωο）和倍频光（2ωο）之间的时间延迟改变时，所产生的三次谐波（THG）的光谱特性。研究结果表明，空气中双色场飞秒激光诱导三次谐波的强度随基频光与倍频光之间的时间延迟而变化，并呈现周期性的调制现象。理论分析指出这是由于基频光的三倍频过程和基频光与倍频光的四波混频（FWM）过程两种物理机制所产生的三次谐波发生了干涉现象。同时研究了基频脉冲与倍频脉冲的啁啾和自相位调制（SPM）对于所产生的三次谐波光谱分布的影响。该研究为双色场飞秒激光诱导三次谐波的相干控制提供了基本的理论依据。

英文摘要：

This paper theoretically studies the spectral characteristics of the third harmonic generated （THG） in air by focusing a two-color-field laser, which is synthesized by a femtosecond laser pulse （ωο） and its second harmonic （2ωο）. It is found that the third harmonic intensity varies as a function of the temporal delay between the fundamental and the second harmonic wave, showing a pronounced periodic modulation. This observation is explained by the interference taking place between two third harmonic sources. One is induced by the direct third harmonic generation of the fundamental wave, while the other is given rise by the four-wave mixing （FWM） of the fundamental and the second harmonic waves. In addition, the third harmonic spectra are investigated when the chirp and the self-phase modulation （SPM） of the fundamental pulse and the second harmonic are taken into account. Our results can provide some key informations for the coherent control of the third harmonic generation induced by two- color-field femtosecond laser in air.