Low-temperature lasing action in a metal-backed monosubstituted polyacetyleneOptically pumped organic polymer lasers are fabricated by spin coating a thin polymer film onto a nanopatterned SiO 2 circular-grating surface-emitting distributed Bragg reflector. For certain grating parameters, we observe a peak inside the stop band that leads to lasing with a reduced threshold. An analytical model, based on the transfer-matrix method, has been developed to investigate the origin of this peak. The theoretical results are in good agreement with the experimental findings.

We present general optimization arguments for resonator-based all-optical switching. Several generic resonator geometries, namely Fabry-Perot resonators, circular gratings as well as micro-ring resonators, are discussed and their particular features highlighted. We establish analytical models which allow a direct comparison of the different all-optical switch geometries. For the parameter range investigated, we find a clear advantage of photonic band-gap resonators (based on Bragg-type reflection) over micro-ring resonators (based on total internal reflection).

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-Introduction. The aim of our research was to test various techniques of packaging for dates stuffed with almond paste and Deglet Nour natural dates, products of national economic interest in Tunisia. Effects of storage temperatures and packaging types were studied from yeast and mold evolution and water content of stored products. Materials and methods. Natural or stuffed date storage was evaluated by using four packaging types: setting the products in an amorphous polyethylene terephthalate small wrapping (APET) with simple sealing; vacuum packaging or modified atmosphere packaging with injection of two different amounts of a gas mixture (20% CO 2 and 80% N 2 ). The sample storage was carried out at three temperatures [(20, 30 and 40) °C] to cause and accelerate the ageing of the dates and, thus, evaluate their shelf life. Results and discussion. Vacuum and modified atmosphere packaging made it possible to decrease the date dehydration during storage. While being based on the product water content, the stuffed date packaging stored under 20 °C in small APET wrappings and having received a 10% gas mixture injection made it possible to obtain a shelf life equal to 6.6 months compared with 4.2 months observed in the case of a simple sealing of these wrappings. For natural dates stored under 20 °C, the application of a partial vacuum packaging increased the shelf life from 3.8 months, obtained for a simple sealing, to 9 months. Conclusion. The use of specific packaging techniques would thus make it possible to preserve for longer the initial stored date quality. The vacuum packaging of natural dates is the most adapted to better protection of the product against yeast and mold proliferation and against dehydration. For stuffed dates, modified atmosphere packaging with a 10% gas mixture injection proved to be the best for preserving the initial quality of the product during its storage.Tunisia / Phoenix dactylifera / packaging / controlled atmosphere storage / vacuum packaging / keeping quality / microorganisms Effet de différents conditionnements sous vide ou sous atmosphère modifiée sur la conservation de dattes Deglet Nour en Tunisie.Résumé -Introduction. L'objectif de nos recherches a été de tester différentes techniques de conditionnement de dattes Deglet Nour naturelles et de dattes fourrées à la pâte d'amande, produits d'intérêt économique national en Tunisie. Les effets de la température d'entreposage et du type de conditionnement ont été étudiés par rapport à l'évolution des levures et moisissures et de la teneur en eau des produits stockés. Matériel et méthodes. La conservation des dattes (naturelles ou fourrées) stockées a été évaluée en utilisant quatre modes de conditionnement : mise en barquettes de polyéthylène téréphtalate amorphe (APET) avec simple scellage ; conditionnement sous vide ou emballage sous atmosphère modifiée avec injection de deux différentes doses d'un mélange gazeux (20 % CO 2 et 80 % N 2 ). L'entreposage des échantillons a été effectué à trois températures [(20, 30 et 40)°...