| Multiphoton processes are emerging as a significant class of phenomena. Accelerated growth in nanotechnology has led to new materials with unique physical and optical properties that have never been observed before. These developments have given rise to potential new applications and devices with physical properties that can far exceed those of traditional materials/systems. And we investigated multi-photon and multi-pulse train processes. First, we investigate novel materials with large third order nonlinearity consisting of semiconductor quantum dots in organic materials. We show that semiconductor quantum dots in an organic host matrix lead to significant enhancement of two-photon absorption. We developed a new synthesis method, and obtained CdS quantum dots using a surfactant as capping agent (decylamine). Historically, the formation of colloidal quantum dot preparation was sufficient for their use. However, for use as absorbers and other devices, the technology must be extended to the formation of thin films of these materials. Therefore we made the first, to our knowledge, optically transparent thin films of colloidal semiconductor quantum dots in reversed micelle structure using polystyrene matrixes. This advancement in material processing is a key enabling tool, which may lead to a new era by providing nanosturctured composite materials with large third-order optical nonlinearity. The beta value of CdS we obtained is 788cm/GW, and this TPA coefficient is almost two orders of magnitude greater than that for bulk CdS. The thin film preparation method is very general and can be adapted to other kinds of semiconductor quantum dot material. We also used our technique for CdSe QD capped with reverse micelle, and we observe the beta value of 304cm/GW.; Second, we used numerical technique, previously developed by Professor Potasek, to investigate hybrid two-photon processes and multi-pulse trains. Many of the chromophores with large two-photon absorption are hybrid materials in which the two-photon absorption is coupled to an excited state absorption. This coupling makes the detailed analysis of the photophysics much more complex. Professor Potasek's numerical method agrees very well with published results. We also examined the details of the carrier dynamics for femtosecond pulses, which also are also in agreement with experimental results. |
