Imazawa R, Kawano Y, Ono T, Kusama Y
Japan Atomic Energy Agency, Naka, Ibaraki, Japan.
Rev Sci Instrum. 2011 Feb;82(2):023116. doi: 10.1063/1.3541810.
A new concept of a terrace retro-reflector array (TERRA) as part of the poloidal polarimeter for ITER is proposed in this paper. TERRA reflects a laser light even from a high incident angle in the direction of the incident-light path, while a conventional retro-reflector array cannot. Besides, TERRA can be installed in a smaller space than a corner-cube retro-reflector. In an optical sense, TERRA is equivalent to a Littrow grating, the blaze angle of which varies, depending on the incident angle. The reflected light generates a bright and dark fringe, and the bright fringe is required to travel along the incident-light path to achieve the objects of laser-aided diagnostics. In order to investigate the propagation properties of laser light reflected by TERRA, we have developed a new diffraction formula. Conditions for the propagation of the bright fringe in the direction of the incident light have been obtained using the Littrow grating model and have been confirmed in a simulation applying the new diffraction formula. Finally, we have designed laser transmission optics using TERRA for the ITER poloidal polarimeter and have calculated the light propagation of the system. The optical design obtains a high transmission efficiency, with 88.6% of the incident power returned. These results demonstrate the feasibility of applying TERRA to the ITER poloidal polarimeter.
本文提出了一种新型台面后向反射镜阵列（TERRA）的概念，它是ITER极向偏振仪的一部分。TERRA即使在高入射角情况下也能将激光沿入射光路径方向反射回去，而传统的后向反射镜阵列则无法做到。此外，TERRA比角锥后向反射镜占用空间更小。从光学角度来看，TERRA相当于一个利特罗光栅，其闪耀角随入射角变化。反射光会产生明暗条纹，为实现激光辅助诊断的目标，需要亮条纹沿入射光路径传播。为了研究TERRA反射激光的传播特性，我们推导了一个新的衍射公式。利用利特罗光栅模型得出了亮条纹在入射光方向传播的条件，并通过应用新衍射公式的模拟得到了证实。最后，我们为ITER极向偏振仪设计了使用TERRA的激光传输光学系统，并计算了该系统的光传播情况。光学设计实现了高传输效率，有88.6%的入射功率被返回。这些结果证明了将TERRA应用于ITER极向偏振仪的可行性。
