Laser Beam Shaping with Optically Patterned Liquid Crystals

Current laser beam shapers such as those used in the OMEGA EP laser system for spatial gain precompensation are made of small metal pixels arranged in a pattern to create a beam shaping device. Laser beam shapers can also be made from liquid crystals (LCs). Because of their unique properties, LCs can be oriented so that they transmit, block, or change the phase of incident light when viewed with the aid of polarizers. This orientation is controlled by a polymer alignment layer in close contact with the LC material. If this alignment layer is a linearly photopolymerizable polymer (LPP) and it is irradiated with polarized UV light, the LC molecules will align along the polymer chains. Irradiating the LPP through a mask, followed by rotating the substrate and irradiating again without the mask, allows the orientation of LCs in different regions of the substrate to be controlled. This process can be used to produce pixellated LC devices that function similarly to metal beam shapers, with both a greater variety of optical effects and a substantially higher laser damage threshold. Future applications of these devices could include erasable and rewriteable beam shapers and apodizers