Beam collimation in the presence of aberrations

This paper describes the application of multiple beam shearing interferomet ry to beam collimation in the presence of lens aberrations. To realize mult iple beam shearing interferometry, a shear plate is used, wedged slightly i n thickness at an angle of 2.7 ", with coatings of 90% reflectance. The bea m collimation in the presence of aberrations is analyzed in terms of the ef fects apparent at the paraxial focus, circle of least confusion and margina l focus. It is shown to be possible to collimate a beam very accurately by moving a lens under test around the position of circle of least confusion w hile observing the fringe line. (C) 2001 Elsevier Science B.V. All rights r eserved.