Lithographic fabrication of large diffractive optical elements on a concave lens surface

We demonstrate experimentally the lithography technique to fabricate a large computer-generated diffractive optical element (DOE) pattern on a concave lens surface with precise alignment by using a laser direct writer. We obtained photoresist film with uniform thickness on the large concave substrate by selecting proper spin-coating parameters, which mainly involve spin rate, spin acceleration, and viscosity of the photoresist. We obtained a square line profile on the concave lens surface. We can write lines that range in width from 0.7 to 10 microm using a single pass of the laser beam. We have designed and fabricated a grating on the concave lens surface using the laser direct writing lithography technique. It is believed that this technique can also transfer large DOE patterns, with a continuous surface relief, onto a convex or concave lens (mirror) surface.