Optically robust photoalignment materials for liquid crystal device applications in the near-UV region (Conference Presentation)

Abstract

Photo-alignment technology is important for liquid crystal (LC) device applications where both high resistance to incident optical energy and spatially distributed alignment states over the device clear aperture are required. Coumarin-based photo-alignment materials developed at the Laboratory for Laser Energetics (LLE) possess near-IR laser damage resistance approaching that of fused silica and have been employed in the development and fabrication of a wide variety of LC high-peak-power laser optics. One example is a photo-patterned LC beam shaper, developed for use in LLE’s four-beam, petawatt-peak-power OMEGA EP laser, that has demonstrated 1054-nm, 1 ns laser-damage thresholds approaching those of dielectric thin-film Brewster’s angle polarizers (30 to 40 J/cm2). Achieving similar performance levels in LC devices for near-UV applications is challenging due to a scarcity of both UV-transparent LC materials and polymer alignment layers that can withstand repeated exposure to intense pulsed- or CW UV irradiation without degradation. Previously-employed alignment materials for UV-LC devices such as buffed polyvinyl alcohol (PVA) or Nylon 6/6 have limited usefulness; buffing embeds particulates and scratches into the alignment layer that reduce its UV damage thresholds to only a few J/cm2 and is incapable of producing highly resolved and spatially-distributed LC alignment states. In recent experiments, we have found that coumarin photoalignment materials are remarkably more resistant to damage from both incident 351 nm, 1 ns high-energy laser pulses [~11.42 J/cm2 (1-on-1) and ~15.70 J/cm2.(N-on-1)] and broad-band, continuous wave (CW) UV-visible light than would be expected due to their highly conjugated aromatic electronic structures. This finding opens a new chapter in the development of LC devices for UV applications in high-peak-power lasers (e.g. wave plates, polarization rotators, radial polarization converters, photo-patterned beam shapers) and other areas of optics and photonics where UV stability is important (e.g., space-based applications).