Position Measurement Method Using a Divergent Laser Beam and Arago Spot for Tracking of an Inertial Fusion Energy Target

Abstract

This paper is a complement to our previous work [Jpn. J. Appl. Phys. 46 (2007) 6000] on the accuracy of the position measurement method using an Arago spot for an inertial fusion energy target tracking system and we here report an improvement of the measurement accuracy using a divergent laser beam. By employing divergent beam illumination, we can magnify the displacement of the Arago spot compared with the actual displacement of the target without enlarging the diameter of the Arago spot significantly, allowing us to measure the small displacement of the target with high accuracy over a large measurement range. The experimental results for a 5-mm-diameter target demonstrated that a measurement accuracy of lower than 0.2 µm can be achieved when the distance between the target and a charge-coupled device camera is within the range from 2 to 10 m.