Simple and Accurate Propagation-Angle Observation of a Collimated Laser Beam within a Short Optical Path Range by Use of a Dual-Focus Fresnel Lens.

We propose a method for observing the propagation-angle displacement of a collimated beam with respect to the travel direction of a moving part by use of a dual-focus Fresnel lens. The fabricated binary-type dual focus Fresnel lens consisting of two portions having a different focal length from each other. 0.5 mrad angular accuracy within a travel range of 16 mm was experimentally confirmed and then it was successfully applied to split-type optical head manufacturing. [ABSTRACT FROM AUTHOR]