Direct laser writing of surface relief microstructures on azopolymer films using structured polarization is an emerging technology for the fabrication of diffractive optics. Films are photopatterned with 488 nm laser light and a spatial light modulator (SLM) configured as a polarization modulator. The structures require no post-exposure processing, and can be replicated using nanoimprint lithography. A limitation of this method is that typical exposure areas are of order 1 mm2. Larger areas require XY stepping of the film, degrading the diffractive functionality due to the stitched boundaries between exposures. Here we report that continuous scanning of the film in the structured polarized illumination reduces boundary structure effects. This has been previously demonstrated in photochemical materials such as photoresist, and it is effective in photomechanical azopolymers since the characteristically slow response enables a surface-averaging that results in relief gratings of highly uniform amplitude. Additionally, the surface relief amplitude and period can be continuously varied via direct programming of the SLM and scan rate. We use the system to fabricate a variety of sinusoidal surface relief gratings of area 25 mm2 which were replicated via nanoimprint lithography and which exhibited first order diffraction efficiencies approaching 33% at 633 nm. We also fabricated chirped gratings designed to diffract RGB along a common direction in first order, with custom color generation based on grating area.
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