体全息光栅偏移布拉格角读出时衍射角的测定

Experimental determination of the diffraction angle of volume holographic gratings under off-bragg condition

体全息光栅的读出偏离布拉格条件时,衍射光方向的确定是体光栅耦合波理论中的一个重要问题。前人(例如Kogelnik和Heaton)对此有两种不同的假设,基于这两种假设算出的衍射光方向有一定差别。我们设计实验,较精确地测量了透射式和反射式光栅在不同写入条件下衍射光方向随读出光角度变化的规律。实验结果表明,衍射光的方向并不是简单地符合某种假设,而是与两写入光的角度和光栅的倾斜度有很大关系。特别是对反射式全息图,光栅矢量的倾斜角越大,衍射光方向越接近于Kogelnik的假设。反之,衍射光方向越接近于Heaton等人的假设。

When a volume holographic grating is readout under off- Bragg condition, determining the direction of the diffracted beam is an important issue in the coupled - wave theory of volume gratings. Previous authors （ Kogelnik and Heaton et all presented two different assumptions about this subject, leading to different diffracted angles. In this paper, we designed experiments to accurately measure the dependence of the direction of diffracted beam on the direction of replay beam. The experimental measurements have been conducted for both transmission and reflection holograms, under various recording conditions. The results show that, the direction of diffracted beam does not simply accord with one assumption, and it has a close relation with the recording angle and the grating slant angle. Especially, in the case of reflection holograms, when the grating slant angle is lair, the diffracted beam＇ s direction agrees mere with Kogelnik＇ s assumption, and vice versa.