各位大大，最近我在看一篇二区的
论文，题目是Grating_micro-dot_patterned_light_guide_plates_for_LED_backlights，Seung Ryong Park，2007。作者在里面提到，团队的
导光板设计理念是通过在导光板上表面刻正弦型
光栅，使得光以衍射-1级主级大出射，如图所示。那么在作者所希望达到的出射情况（摘自原文）“when δi=0, all diffracted orders are located in the x-o-z plane as shown in Fig. 2(b). This grating diffraction geometry is referred to as classical “in-plane diffraction.” Under this condition with a sufficiently large incident inclination angle (typically larger than the critical angle), it is possible to make the forward diffracted zero-order vanescent and only the -1st diffracted order to be vertically (in the z-axis direction) out-coupled into air by suitable choice of the grating period”时，这个大于临界角的入射角
光线竟然不会继续在导光板内全反射，而是发生了
衍射，这里我觉得矛盾[了。既然满足全反射的条件却不发生全反射，为什么呢？
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