Multiple tipped berek plate optical retarder elements for use in spectroscopic ellipsometer and polarimeter systems

摘要

Disclosed are retarder systems, for entering retardation between orthogonal components of an electromagnetic beam of radiation, having first and second Berek-type retarders which each present with first and second essentially parallel sides. The first and second Berek- type retarders are oriented, as viewed in side elevation, with first and second sides of one Berek-type retarder being oriented other than parallel to first and second sides of the other Berek-type retarder. During use in a spectroscopic ellipsometer/polarimeter system, a beam of electromagnetic radiation exits in a propagation direction which is essentially undeviated and undisplaced from the direction of an incident beam of electromagnetic radiation, even when the retarder system is caused to rotate about the locus of the beam of electromagnetic radiation. A system with similarly oriented third and fourth Berek-type retarders, sequentially placed after the first and second Berek-type retarders, is also disclosed.