Holographic “Development” of a Hidden UV Image Recorded on a Liquid Crystalline Polymer

Films of a chiral liquid crystalline side chain polymer with azobenzene chromophores are shown to be a novel mediumfor UV image recording. The principle includes a primary process of recording a UV image e.g. of a mask. by unpolarizedUV light excitation of a considerable amount of extraordinary long living cis-isomers of the azo-chromophores. After thatthe image is ‘hidden’ because it is not seen under a polarising microscope equipped with a red filter. At the second stage, theimage is developed by a linearly polarized beam of visible blue or green. light that converts cis-isomers back into theirtrans-counterparts. The image appears in the form of the spatial modulation of the optical anisotropy which is measured ateach stage in situ by an ellipsometry technique. The development of the hidden images has been done both with a uniformillumination and a holographic technique using a grating formed by interfering beams of visible Ar-laser light. Recordedimages are erased by the second, this time uniform, UV irradiation of the film and the process may be repeated many timeson the same spot.