超短脉冲高斯光束在线性色散介质中的远场特性

基于瑞利-索末菲衍射积分公式，在未作近轴近似的条件下，推导出等束宽超短脉冲高斯光束通过线性色散介质的远场公式，并用于研究其远场特性，所得公式可用于大衍射角情况.结果表明，等束宽脉冲高斯光束的频谱上存在一临界角，小于临界角时，出现蓝移；大于临界角时，出现红移，红移量随着衍射角的增大而增大.而脉冲波形将经历时间移动，移动量随衍射角的增大而增大；远场高斯脉冲波形将不再保持不变.此外，群速度色散将引起啁啾，啁啾量随衍射角的增大而减小.

Far-field Properties of Ultrashort Pulsed Gaussian Beams in a Linear Dispersive Medium

Based on the Rayleigh-Sommerfeld diffraction integral,the far-field expression for ultrashort pulsed Gaussian beams with constant waist width in a linear dispersive medium is derived without involving the paraxial approximation,and used to study their far-field properties. The expression is applicable to the large diffraction angle. It is found that there exists a critical diffraction angle θc,for the power spectrum of pulsed Gaussian beams with constant waist width. The spectrum is blue-shifted if θc,whereas,for θ>θc,the spectrum is red-shifted,and the redshift increases with increasing θ. Additionally,there is a time shift,which increases with an increase of θ,and the Gaussian pulse form can not remain unchanged in the far field. Finally,the group velocity dispersion results in the chirp,which increases with decreasing diffraction angle.