Development of a highly-stable alignment monitor for a severe environment

Evaluation and stabilization of a free spectral range of a reference etalon

Abstract

We develop an alignment monitor, which detects 10-micro radian of alignment changes between 40 pieces of platy parts called a vane, which configures a cylindrical detector with a height of approximately 750 mm and a diameter of approximately 600 mm, highly stably in a severe environment of 3T of high magnetic field and vacuum for a term longer than several months. Here, we consider for evaluating and stabilizing a free spectral range of an etalon, which is a length reference for the alignment monitor, with an uncertainty smaller than ppm.