Volume holographic optical element for high-definition imaging

Abstract

Volume holograms exhibit the characteristic of multiple optical functions in a common area by multiple exposure in preparation. From the characteristic, it is expected to be applied to large capacity recording medium and diffractive optical elements with unique functions. In this study, volume holograms are investigated to apply to diffractive optical elements for high-definition imaging of nanostructure. The assumed volume holographic diffractive optical element exhibits a function that light waves from two-point sources with a distance shorter than the wavelength are diffracted as plane waves with different wave vectors. When a volume hologram is prepared by exposing the interference fringes consist of a point source light and a plane wave, a plane wave is diffracted by illuminating a point source light onto the volume hologram. However, the wave vector of the diffracted plane wave is changed and the diffraction efficiency is decreased by shifting the position of the point source light. By wave vector filtering, the diffracted plane wave from a point source at shifted position becomes not to be detected. A volume hologram can be prepared that the point source at the shifted position is diffracted as a plane wave with a different wave vector by multiple exposure. Then, two-point sources can be resolved. The distance between two-point sources is called shift-selectivity. For preparing the volume holographic optical element, a photopolymer with a thickness of 10 mm was used to obtain short shift selectivity. The photopolymer was exposed by using a semiconductor lase with a wavelength of 405 nm. In this condition, a shift selectivity of 100 nm was achieved.