Inline holographic inscription of diffractive lenses in azobenzene molecular glass thin films

A simple inline holographic setup is used to fabricate holographic diffractive lenses using off-the-shelf components. The resulting surface relief gratings are inscribed directly in azobenzene-functionalized thin films with pitches that agree well with a theoretical Fresnel zone plate. The annular gratings have an outer radius of approximately 9 mm and an inner radius of less than 4 mm. Interfering laser beams, circularly polarized in the same direction, generally produce poor-quality gratings in azo-films, but the addition of a reference beam lens greatly improved their consistency and produced quality gratings with depths up to 400 nm. Multiple exposures produce multifocal diffractive lenses, while angling the sample resulted in focal lines, instead of focal points.