GROWTH OF ORGANIC CRYSTALLINE THIN-FILMS, THEIR OPTICAL CHARACTERIZATION AND APPLICATION TO NONLINEAR OPTICS

The currently increasing level of interest confined structures origina tes from both fundamental and applied motivations. Confined molecular structures appear of special interest in view of their high, quadratic , non-linear optical efficiency when adequately designed chromophores are made to crystallize in non-centrosymmetric lattices. Suitable tech niques to grow thin organic crystals are then clearly required. We fir st describe the design and application of a process of thin (similar t o 1 mu m) organic non-linear crystals based on the so-called ''pit'' o r ''inverted bell'' temperature profile. This technique appears partic ularly effective for inhibiting the needle crystallization habit of or ganic materials such as 2-methyl-4-nitroaniline (MNA) and allows the p roduction of non-elongated shapes. This crystallization process is sho wn to provide a way of producing high quality thin organic non-linear crystals for optical investigations. Secondly, we introduce a newly de veloped method for the computation of Briot-Sellmeir and Briot-Cauchy index chromatic dispersion coefficients that involve a minimum of appr oximations. Finally, we discuss some non-linear optical features of mo nocrystalline thin films of MNA in unconfined and confined environment s. We then devote particular attention to femtosecond, broadband frequ ency mixing in non-phase-matched configuration and evidence of harmoni c modes quantization in confined environments. The last series of expe riments is a prerequisite first step towards subsequent extension to t he more general realm of parametric processes in confined environments , which may lead to new types of optical signal processing devices.