Ξ型介质中相对载波包络相位对脉冲特性的影响

Effects of relative carrier-envelope phase on pulse characteristics in a Ξ-type medium

利用数值模拟方法,研究了单光子共振及完全非共振情况下相对载波包络相位(RCEP)φ对在Ξ型三能级原子介质中传播的双色超短脉冲波形及频谱特性的影响。结果表明:在单光子共振情况中,RCEP对双色脉冲的传播形式及频谱特性有显著的控制作用。RCEP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。当φ=π时,在传播过程中,脉冲不再发生分裂,而且脉冲的形状和强度基本保持不变。在完全非共振条件下,脉冲分裂不再发生,比单光子共振情况的频率范围大得多的超连续谱可以被得到。虽然RCEP对脉冲形式和频谱特性的影响不如单光子共振时那样强烈,但改变值φ仍可以使频谱范围及不同频率的强度分布有明显的改变。当φ=0时,可得到频谱更宽、连续性更好、高频分量强度更大的超连续谱。

In the cases of one-photon resonance and complete non-resonance, the effects of the relative carrier-envelope phase（RCEP） φ on pulse form and spectra characteristics of two-color ultrashort laser pulses in a Ξ-type three-level atomic medium are investigated by using numerical simulation.The results show that in the single-photon resonance case the RCEP has evident control role of profile and spectral characteristic of the two-color pulses.The RCEP can decide the amplitude, propagating velocity,pulse splitting case and the number of sub-pulses.When φ=0,the pulse does not split, and the shape and intensity of the pulse keep basically unchanged during the process of propagation.In the case of complete non-resonance, the pulse splitting doesn′t arise again, and the supercontinuum with frequency range much larger than that in the one-photon case can be obtained.Although the effects of RCEP on pulse shape and spectral property are not as strong as those in the one-photon resonance case, varying φ can still make frequency range and intensity distribution at different frequencies vary obviously.When φ=0, the supercontinuum with wider spectral range, better continuity and stronger intensity of high frequency components can be obtained.