激光脉冲啁啾影响双色激光场诱导气体产生太赫兹辐射特性的理论研究

Theoretical study of influence of laser pulse chirp on terahertz emission characteristics of gas induced by two-color laser field

随着太赫兹波研究的深入,研究者们对可调控太赫兹源的需求不断增加.如何获取可调控的太赫兹波一直是太赫兹科学领域的研究热点和关键问题之一.本文通过建立双色激光诱导气体电离光丝产生太赫兹波及其后续传播过程的三维理论模型,详细研究了双色泵浦激光的啁啾参数对飞秒激光场辐射产生太赫兹波的影响.研究结果表明,在激光脉宽为飞秒量级时,以40 fs的情况为例,当啁啾参数在与激光脉宽处于相同的飞秒量级尺度上时,其对太赫兹波的振幅与频谱都产生显著影响.在双色飞秒激光场中,基频波和倍频波的啁啾各自起到不同的作用:基频波的啁啾主要影响太赫兹波的时域波形,而倍频波的啁啾则决定了太赫兹辐射的振幅大小、中心频率与频谱宽度.研究表明,激光啁啾作为一种可控的参数,对所辐射的太赫兹波属性具有多重调制效果,且相关啁啾的作用规律随双色激光的初始相位也呈现规律性变化.这些结果为研究太赫兹辐射的产生与调控提供了新的思路与依据.

With the development of terahertz(THz)wave research,the demand for controllable THz sources is increasing.How to obtain the regulated THz waves has been one of the research hotspots and key problem in the field of THz science.There have been researches in which the resulting THz wave is modulated by changing the wavelength,relative phase,energy,or chirp of the laser produced by a two-color laser.In this work,we establish a three-dimensional theoretical model of THz wave generation and subsequent propagation induced by two-color laser.And we investigate the influence of chirp modulation of different laser on THz wave by chirp modulation of the fundamental wave(FW)and the second harmonic wave(SHW)of two-color laser,including THz wave amplitude,THz wave center frequency and spectrum width,and analyze the physical mechanism of related phenomena.At the same time,the effects of different orders of magnitudes of laser chirp parameters(femtosecond and picosecond)and initial phase of laser pulse on THz wave parameters are also studied.The results are shown below.1)In the two-color laser,the chirp of FW mainly affects the shape of THz wave when the initial phase is unchanged.The chirp modulation of SHW can cause the amplitude of THz wave to change significantly,and affect the center frequency and spectrum width of THz waves.2)In the case of laser pulse width of femtosecond order,40 fs is taken as an example.When the chirp parameter is of femtosecond magnitude,the chirp parameter has a great influence on the THz wave generation efficiency of two-color laser filament.At the picosecond magnitude,the chirp parameter has a weak effect on the THz wave energy and mainly affects the phase of the THz wave.3)The initial phase of the two-color laser can aid in chirp modulation of THz wave to optimize the energy generated.4)The initial phase of two-color laser can assist in the process of chirped laser modulation of terahertz waves to optimize the energy generated.Our research shows that the chirp modulation,as a controllable parameter,has multiple regulation effect on the properties of radiated THz waves.The related research results provide a new idea and basis for studying the generation and regulation of THz waves.