Propagation effects of bichromatic laser pulses on the induced terahertz-radiation generation in a gaseous medium

Abstract

In this work, a simplified propagation model is proposed to specifically study the propagation effects of the driving laser pulse on the terahertz radiation in a gaseous medium for a short propagation distance. The simulations indicate that, due to the atomic ionization process and the energy redistribution between the laser field and the ionized electrons, the bichromatic laser pulses experience significant energy decaying, blue-shift, and a trailing edge broadening. As a result, the behaviors of the ionized electrons in the deformed laser field lead to the blue-shift and the multipeak structures in the terahertz radiation spectrum. Further investigations show that the differences of the terahertz spectrum for different relative phases of the fundamental and the second harmonic fields are gradually fading away as the driving laser pulse propagates. All these results strongly suggest that the propagation effects should be taken into consideration while it is generally disregarded.