【摘要】 飞秒强脉冲激光具有高功率、窄脉宽和宽光谱等特点,其在大气传输过程中涉及很多线性和非线性的物理机制,高阶效应对传输将产生一系列重要的影响。采用数值方法求解包含拉曼延迟响应的非线性传输方程,研究了与拉曼延迟响应时间相当的、具有几十飞秒脉宽的飞秒强激光大气传输中拉曼延迟克尔非线性效应引起的非线性折射率变化、自聚焦和光谱展宽特性。数值结果表明:拉曼延迟克尔非线性效应的存在使得非线性折射率的峰值减小并向脉冲尾部偏移,随着拉曼延迟响应所占比例的增加,这种现象越明显;轴上光强分布不再沿脉冲中心对称,自聚焦效应首先发生在脉冲的尾部,并且减弱了光束的非线性自聚焦效应;拉曼延迟克尔非线性效应引起的长波频谱增量成分大于短波频谱增量成分,使展宽后频谱中心发生了红移;初始脉宽0τ越小,拉曼延迟响应对传输特性的影响越大。更多还原

【Abstract】 The propagation of strong femtosecond laser pulses,which have characteristics of high-power,short pulse-width and wide spectrum,involves many linear and nonlinear effects.So,higher-order effects have important impacts on the propagation.The nonlinear propagation equation with the delayed Raman Kerr response is solved numerically.In the article,the properties of nonlinear refractive index,self-focusing and spectrum broadening due to Raman delayed Kerr nonlinearity of strong femtosecond pulses propagating in atmosphere are studied.The pulse width is as short as tens of femtosecond,or as almost the Raman delayed Kerr response time.The numerical results show that Raman delayed Kerr nonlinearity lowers the maximal nonlinear refractive index,moves the peak value to the tail part of the pulse.These phenomenon become more obvious with the increase of Raman delayed Kerr nonlinearity.And it makes the distribution of on-axis intensity asymmetrical.The self-focusing occurs firstly in the trailing part of the pulse,which weakens the effect of self-focusing.Raman delayed Kerr nonlinearity also generates more frequency shifts to long wave than to short wave,which produces a red-shift to the center of broadening spectrum.The simulation results also indicate that the shorter the initial pulse width,the larger impact of Raman delayed response to the propagation.更多还原