Ladder型介质中双色超短脉冲共振传播的RCEP控制

RCEP CONTROL OF TWO -COLOR ULTRASHORT PULSES FOR RESONANCE PROPAGATING IN A LADDER- TYPE MEDIUM

利用不含慢变振幅近似（SVEA）和旋波近似（RWA）的全波Maxwell—Bloch方程组的数值解，研究了单光子共振（即两个脉冲的中心频率分别与原子系统两个跃迁频率相等）情况中，在ladder型三能级原子介质中双色超短激光脉冲传播行为对相对载波包络位相（RCEP，以下简称相对位相）的依赖性．结果表明：相对位相对小面积双色脉冲的传播波形及频谱特性有显著的控制作用．相对位相的大小可以决定脉冲振幅大小、传播速度快慢、脉冲分裂与否及子脉冲数目多少．通过改变相对位相的数值可以获得更宽的频谱宽度及更高的光谱强度特别是高频分量的光谱强度．当双色脉冲面积增大时，相对位相对脉冲波形及频谱特性的控制作用有所减弱．

In the cases of single - photon resonance （ i. e. the central frequencies of two pulses are equal to two transition frequencies of the atomic system, respectively）, relative cartier- envelope phase （RCEP, below called briefly as relative phase） dependence of the propagation behavior of two - color ＇ultrashort laser pulses in a ladder - type three - level atomic medium is investigated by using the numerical solution of the Maxwell - Bloch equations without the slowly varying envelope （SVEA） and rotating - wave approximations （RWA）. The study result shows that relative phase has evident control role for profile and spectral characteristic of the two - color pulses with small area. The size of relative phase decides the amplitude, propagating velocity, pulse splitting case and number of the sub - pulses. By changing the values of relative phase, broader spectral width and higher spectral intensity, especially the spectral intensity of higher frequency components, can be obtained. When the area of two - color pulse is increased, control role of relative phase on pulse profile and spectral characteristic is decreased.