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Reversible holographic storage media are very useful for temporal storage of a buffer hologram, in associative retrieval, and photo-EMF detection. A particularly interesting application is optical coherence tomography (OCT), a noninvasive medical imaging method. Skin tissue or bone are highly scattering media, but nevertheless exhibit a transparence window in the NIR of the light spectrum (800-850 nm). Ballistic photons coming from a certain depth within the medium can be separated from diffusely scattered photons by holographic time gating enabling depth-resolved holographic imaging.
Due to the extremely low number of ballistic in comparison with scattered photons, this technique requires holographic storage media with very high sensitivity in the NIR. The necessity to use NIR light excludes most commonly used reversible holographic media,
such as Bakteriorhodopsin or azo-dye-containing systems to name only a few. By contrast, photorefractive (PR) materials, in particular amorphous organic PR systems, are highly promising for this application. However, their NIR performance is insufficient so far. In this paper, we introduce a novel organic PR material, a composite based on the poly(arylene vinylene) copolymer TPD-PPV (inset Fig. 2). Under normal conditions, the material exhibits a reasonably fast hologram recording speed in the NIR, much faster than more traditional (e.g. PVK-based) materials under identical conditions. With this material, we discovered that pre-illumination (“gating”) improves the sensitivity by a factor of > 50. These effects are reversible, but can be partly permanent by redox-chemical doping. We demonstrate multiple-video-rate holographic recording under practical conditions, underlining the outstanding NIR-sensitivity of the new material.
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