为了证明由周期性造成的光的“负折射”现象不同于光的衍射现象,采用光学外差干涉法,对运动的平面光栅的衍射光进行多普勒频移的测量.通过对参考光引进频移的方法,让拍频值和参考光频移值对比确定衍射光所发生的多普勒频移的正负,验证了周期性的平面光栅当入射光与出射的衍射光在法线同一侧时发生的多普勒频移是正常的.说明仅由周期性造成的“负折射”现象,并不能产生反常多普勒效应；具有反常多普勒频移的周期性二维光子晶体才具有反常的等效负折射率,“左手”材料的反常性质并不仅是由于周期性造成的.%Optical heterodyne interfering is used to measure the Doppler shift of diffraction beam of moving plane grating to demonstrate that the"negative refraction phenomenon"caused by periodicity is different from the diffraction phenomenon. By introducing Doppler shift in reference beam and contrasting the final beat frequency, the Doppler shift is measured to be normal when incident light and diffraction light are in the same side of normal of periodic plane grating, which indicates that the abnormal Doppler shift can not occur on the material with "negative refraction phenomenon" caused by periodicity. Periodic two-dimensional photonic crystal with the property of abnormal Doppler shift has equivalent negative refractive index, and abnormal properties of left-handed materials are not exclusively caused by periodicity.
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