DOUBLE PASS INTERFEROMETRIC ENCODER SYSTEM

摘要

PROBLEM TO BE SOLVED: To provide a preferred double pass interferometric encoder system.SOLUTION: An encoder head (110) includes one or more components arranged to: i) direct a first incident beam to a diffractive encoder scale (105) at a first incident angle with respect to the diffractive encoder scale (105); ii) receive a first return beam from the diffractive encoder scale (105) at a first return angle that is different from the first incident angle; iii) redirect the first return beam to the diffractive encoder scale (105) as a second incident beam at a second incident angle; and iv) receive a second return beam back from the diffractive encoder scale (105) at a second return angle that is different from the second incident angle. Difference between the first incident angle and the second incident angle is smaller than difference between the first incident angle and the first return angle, and smaller than difference between the second incident angle and the second return angle.