Nonlinear Electro-Optical and Holographic Storage Effect in Fullerene-Doped Nematic Liquid Crystal Film

Abstract

There have been intense research interests in materials capable of recording holographic planar or volume gratings. These include inorganic [1] and polymeric [2] photorefractive crystals, liquid crystals [3–5], bacteriorhodopsin [6], semiconductors [7] and glasses [8]. There are various advantages and limitations associated with these storage materials. In photorefractive materials, for example, fixing the optically written holograms requires the use of high fields and/or time consuming large temperature cyclings. The liquid crystalline systems [3–5] that have been investigated in the context of persistent grating also involve large laser induced temperature and phase changes. More recent work [6–9] on other materials have shown promises in overcoming some of these limitations. We have previously reported dc field assisted transient grating effects in untreated and dye-doped nematic liquid crystal film [10]. In this paper, we describe the observation of permanent grating formation in Fullerene C₆₀-doped nematic liquid crystal film. In very lightly doped and practically totally transparent thin nematic films, permanent gratings can be generated with unfocused milliwatt power laser with the aid of dc voltages around 1 volt or so. Diffraction efficiency of over 10%, and grating constant ≲ 10 μm can be realized in these materials. These holographic gratings can be electronically turned off and on at millisecond speed.