Design and fabrication of large-format holographic lenses

摘要

Dichromated gelatin layers (DCG) facilitate the design and fabrication of large-format (1 m$+2$/) holographic optical elements (HOE) that exhibit high optical quality and diffraction efficiency. The subject matter of this report is the presentation of an optimized design and fabrication technique for the manufacturing of large-format diffractive optics. The emphasis is placed on the realization of homogeneous diffraction efficiency distribution across the aperture of the HOE. The nature of the holographic process requires precise control of the mechanical properties of the DCG layer such as moisture content, shrinking, swelling, hardness, and elasticity of the film, which specify the slant angle, the mean index of refraction, and the amplitude of the refractive index modulation. These properties ensure the attainment of the desired diffraction efficiency, bandwidth, and Bragg-shift. The results achieved in the development and fabrication of such layers are presented and their applicability as holographic solar concentrators is explained. The emphasis is also placed upon the development and realization of a novel copying technique for the batch reproduction and inexpensive manufacturing of large-format transmissive holograms that are used as focusing lenses in solar concentrators.