Single-step photofabrication of kinoforms in use of azobenzene-containing polymer films

We propose a new method of optically fabricating kinoforms using polyester containing cyanoazobenzene units in the side chain. This method utilizes the surface relief structures induced optically on the azopolymer films. Using a gray-tone amplitude mask with black and white lines as a spatial light modulator, we constructed the surface relief structures on the azopolymer films with an argon-ion laser beam (488nm). The relief depths constructed were deep enough to provide a wide range of visible light with a phase difference of 2pi. In addition, irradiation on the azopolymer film with a spatially modulated light that had multilevel intensities inscribed the multilevel relief structure reflecting the intensity modulation. This property is applicable to the fabrication of diffractive optical elements, especially kinoforms, because the multilevel relief structure provides an incident light with phase modulation. We designed a phase pattern for a kinoform by computation and expressed it as a gray-tone amplitude mask. Irradiation on the film through the gray-tone mask with the pump beam inscribed a multilevel relief structure that diffracted an incident light to produce a desired image. The desired image appeared without the effect of the internal refractive index modulation of the film. We, therefore, confirmed a possibility of fabricating a kinoform with a multilevel relief structure on the azopolymer film. Since our fabrication method for kinoforms requires only exposure, it has a significant advantage over other techniques that require additional processes such as developing and etching.