I. Theoretical deduction According to: Eox=0=0 Z=0: M7 b∥/Eek i cOS x sin Eoe ! z=d ik. d cOS x sin 6 y Eo/e"d 0 k2 ∴k2a=nn→ksPn ,(P=0,,2,3…)0 0 z 0 x z a E = = According to: = 2 cos sin 0 ( 0 0 ) g g g ik z ik z c m m n k i x y E e E e a k a b        −     − =     ’  = E E 0 0 ’ 2 cos sin 0 0 ( ) g g g ik d ik d c m m n k i x y E e e a k a b        −     − =     ,( 0 1,2,3 ) g g p k d p k p d   =  = =  ， …… Z=0: Z=d: I. Theoretical deduction