Growth of organic crystalline thin films, their optical characterization and application to non-linear optics

Abstract

The currently increasing level of interest in quantum confined structures originates 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 techniques to grow thin organic crystals are then clearly required. We first describe the design and application of a process of thin (∼ 1 μm) organic non-linear crystals based on the so-called “pit” or “inverted bell” temperature profile. This technique appears particularly effective for inhibiting the needle crystallization habit of organic materials such as 2-methyl-4-nitroaniline (MNA) and allows the production of non-elongated shapes. This crystallization process is shown to provide a way of producing high quality thin organic non-linear crystals for optical investigations. Secondly, we introduce a newly developed method for the computation of Briot-Sellmeir and Broit-Cauchy index chromatic dispersion coefficients that involve a minimum of approximations. Finally, we discuss some non-linear optical features of monocrystalline thin films of MNA in unconfined and confined environments. We then devote particular attention to femtosecond, broadband frequency mixing in non-phase-matched configuration and evidence of harmonic modes quantization in confined environments. The last series of experiments is a prerequisite first step towards subsequent extension to the more general realm of parametric processes in confined environments, which may lead to new types of optical signal processing devices.