Photoaligned liquid-crystal polymers create vortex retarders

Optical designers require radially and azimuthally polarized beams to improve performance of systems like confocal microscopes and lithography systems. Scientists at JDSU (Santa Rosa, CA) and the University of Arizona (Tucson, AZ) recently reported the use of photoaligned liquid-crystal polymers (LCP) to develop vortex retarders—monolithic components that have constant retardance but a fast axis rotating around a point. To create half-wave vortex retarders with a continuously varying fast axis of m = 1, 2, 3 modes at 550 nm, the researchers fabricated samples on 2 in. squares of Corning 1737F glass with a broadband antireflection coating and a photoalignment layer set via exposure to linearly polarized ultraviolet light. The thickness of the LCP determined the retardance value. The team analyzed the elements theoretically and experimentally by comparing the expected space-variant Mueller matrix of each component to the measured one. The measured and calculated point-spread matrix showed close agreement, and the samples showed excellent retardance uniformity of 98.5%. Such polarization components of single or higher orders are useful in creating nondiffracting Bessel fields, which can be used to enlarge the particle-trapping region of optical tweezers. Contact Scott McEldowney at [email protected].