{'fraction_non_alphanumeric': 0.024291497975708502, 'fraction_numerical': 0.0155195681511471, 'mean_word_length': 5.257383966244726, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Photorefractive polymers with improved efficiency

Recently, photorefractive polymers have emerged as promising recording media for holographic storage and optical processing such as optical correlation devices.',' Because of their structural flexibility, these new materials could be optimized and materials with fully reversible refractive index modulation of An = 7 X 10K3 have been developed leading to nearly 100% diffraction efficiency in 105-pmthick samples.' However, the high electric field that needs to be applied (50-100 V/pm) to these polymers to reach that level of performance is a limitation. Thus there is a need for photorefractive polymers doped with more efficient chromophores. Here, we present a new photorefractive polymer composite based on a PVK matrix and doped with the new chromophore HR-254. The photorefractive properties of these new composites are studied by four-wave mixing and two-beam coupling experiments. The chromophore, whose structure is shown in the inset of Fig. 1, has been designed to lead to an efficient orientational effect in low glass transition temperature ( T,) photorefractive polymers. The chromophore has an absorption maximum at 500 nm as shown in Fig. 1. The structure of the molecule has been carefully designed to prevent photoisomerization and to ensure good solubility in the photoconducting matrix and to prevent crystallization. The nonlinear response of the chromophore was measured with the frequency-dependent ellip-