双色场相位平缓对远场前向太赫兹的增强  

Enhanced far field terahertz in forward direction due to relative phase flatten of two-color field

作　　者：白亚[1] 许荣杰[1] 宋立伟[1] 刘鹏[1] 李儒新[1] 徐至展[1] 

机构地区：[1]中国科学院上海光学精密机械研究所强场激光物理国家重点实验室,上海201800

出　　处：《红外与激光工程》2014年第8期2656-2661,共6页Infrared and Laser Engineering

基　　金：国家自然科学基金(11274326;60978012;11134010;11127901);国家973计划(2011CB808103)

摘　　要：太赫兹辐射极性和幅度依赖于双色场相位。由于等离子体光丝中色散和Gouy相移,导致双色场的相对相位随着激光的传播发生改变。当相位的改变量大于π时,丝中的太赫兹电场极性发生反转,使得远场太赫兹辐射在离轴相位匹配角方向相干增强,而光轴前向相消减弱。通过对基频和倍频聚焦条件的调整和传输非线性色散的作用对双色场相对相位进行了调制,提出了可以使相对相位平缓的方法。模型计算证明了等离子体形成和Gouy相移调制是使双色场相移变平缓的原因。随后利用相位变平缓的条件得到了太赫兹发生极性反转的失相长度延长,最大长度近三倍于空气介质中的失相长度。在满足相位变平的条件下,远场太赫兹辐射在光轴前向的分布得到增强。Pumped by two-color field, generated THz field amplitude and polarity depend on relative phase between two frequencies. Due to dispersion in plasma filament and Gouy phase shift, relative phase of two-color field varies along laser propagation direction. As the phase changed by 7r, local THz field in filament got polarity reversal, far field THz constructive enhanced in off-axis direction, while destructive interference in forward direction. By adjusting the focusing geometry for two frequencies and through nonlinear dispersion in plasma filament the relative phase of two-color field was modulated. It was found that the relative phase flattens by the plasma formation and the conditions of focusing geometry. The dephasing length of THz fields that maintaining its polarity was elongated, with maximum value three times larger than dephasing length in ambient air. The far field THz radiation was enhanced in forward direction near the propagation axis.

关 键 词：双色场相位 Gouy相移 失相长度 太赫兹辐射 

分 类 号：O437[机械工程—光学工程]