A review of selected technological applications of DCG holograms

Abstract

The subject matter of this presentation is to demonstrate the engineering applications of holographic optical elements (HOEs) fabricated in dichromated gelatin (DCG) films exhibiting enhanced properties. The composition, structure and the physical, chemical and optical properties of the DCG-film are briefly described in the introduction that is followed by detailed discussion of the developing processes used to achieve the necessary holographic characteristics required by the various applications. Other procedures are used to achieve explicit objectives, e.g., controlling the spectral characteristics of the HOE by inorganic and/or organic additives and using filler material to enhance the UV or IR performance. Stress induced by environmental forces, e.g., wind, or by mechanical strain also changes the performance of the HOE and may be exploited in engineering applications. The optical characteristics of the HOE are also modified by internally induced stress, such as changing the water content of the polymer or using cross-linking agents to modify and harden the gelatin matrix. The formation of thermal or density gradients in the gelatin film during the coating process or at some stage of the hologram development have also an effect on the holographic properties for they determine the conformational state and the mechanical strength of the gelatin film. The ratio between the coiled and the helical structures in the gelatin matrix determines the optical and mechanical properties of the holographic film. Multiple exposures are used to record up to four holograms in single DCG film that are used to reconstruct concurrently several monochrome or RGB beams.

Holographic lenses for building integrated concentrating photovoltaics

“…Dichromated gelatine (DCG) emulsion is a holographic material which has been successfully used to record volume gratings to act as solar concentrators [5,6,8,11] due to its optical characteristics, such as high dynamic range of refractive index modulation [12,13], high diffraction efficiency (with values near to 100%), low scattering, low absorption and high spatial resolution [14].…”

Characterization of volume holographic optical elements recorded in Bayfol HX photopolymer for solar photovoltaic applications

“…Two kinds of photosensitive materials proven to be suitable for the recording of holographic lenses as solar concentrators are dichromated gelatin (DCG) [5,[8][9][10][11] and photopolymers [12][13][14]. Both of these materials can be self-produced or acquired from manufacturing companies and provide high efficiency, resolution, index modulation and transparency.…”