Liquid crystal near-IR laser beam shapers employing photoaddressable alignment layers for high-peak-power applications

Large-scale, high-energy Nd:glass laser systems require beam shapers to control the spatial distribution of the incident intensity. Commercially available liquid crystal (LC) electro-optical spatial light modulators (SLM's) are frequently employed for this purpose, but their intrinsic requirement for conductive metal or metal-oxide coatings limits their 1054-nm laser-damage thresholds to 230 mJ/cm(2) (2.4 ns, 5 Hz), relegating them for use only in low-fluence areas of the laser system. Previously, we demonstrated that passive near-IR LC beam shapers employing coumarin alignment layers patterned by contact photolithography are capable of high resolution and contrast and can withstand incident 1054-nm laser-fluence levels of >30 J/cm(2) (1-ns pulse). An evolutionary step to expand the scope of this simple and robust device would be to identify and incorporate into the device structure photoalignment layers that trigger LC bulk reorientation by undergoing reversible optical switching between two predetermined alignment patterns using low-energy polarized UV/visible incident light and have a high near-IR laser-damage threshold. Such "optically driven" LC beam shapers offer the in-system write/erase flexibility of the electro-optical LC SLM's while eliminating conductive coatings that compromise the laser-damage threshold and electrical interconnects that increase device fragility and complexity. To this end, we have recently identified and evaluated the 1054-nm laser-damage-resistance and coating properties of several commercial azobenzene-based photoswitchable alignment materials. In 1-on-1 and N-on-1 testing, these new materials displayed 1054-nm laser-damage thresholds that compare very favorably to those of previously tested coumarin photoalignment materials (30 to 60 J/cm(2)).