Terrace retro-reflector array for poloidal polarimeter on ITER
Imazawa, Ryota; Kawano, Yasunori; Ono, Takehiro; Kusama, Yoshinori
A new concept for 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 can not. Besides, TERRA can be installed in a smaller space than a corner-cube retro-reflector. TERRA is equivalent to a Littrow grating in an optical sense, and the reflected light generates a bright and dark fringe. 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. Finally, we have designed laser transmission optics using TERRA for the ITER poloidal polarimeter. 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.