Colour neutral antireflection coatings for strongly curved lenses using organic nanostructures as low-n template

To effectively improve color neutrality of antireflection (AR) coatings, a layer with a very low refractive index (n < 1,3) must be used as the top layer. However, solid materials with such a low refractive index (n) does not exist. The deposition of low molecule weight organic materials as compact films, and a subsequent plasma etching procedure on these films, offered the possibility to produce a nanostructured layer with a very low refractive index as top layer for an antireflection coating. Strongly curved aspheric lenses were coated with such a super-broadband AR design (ARplas2) and the antireflection performance was measured at different locations on the lens. An average reflection < 0,25 % over the full visible wavelength range was measured even in the outermost region of the curvature.