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| Abstract: | Nonlinear optics is a broad field of research and technology that encompasses subject matter in the field of Physics, Chemistry, and Engineering. It is the branch of Optics that describes the behavior of light in nonlinear media, that is, media in which the dielectric polarization P responds nonlinearly to the electric field E of the light. This nonlinearity is typically only observed at very high light intensities. This area has applications in all optical and electro optical devices used for communication, optical storage and optical computing. Many nonlinear optical effects have proved to be versatile probes for understanding basic and applied problems. Nonlinear optical devices use nonlinear dependence of refractive index or absorption coefficient on the applied field. These nonlinear optical devices are passive devices and are referred to as intelligent or smart materials owing to the fact that the sensing, processing and activating functions required for optical processes are inherent to them which are otherwise separate in dynamic devices.The large interest in nonlinear optical crystalline materials has been motivated by their potential use in the fabrication of all-optical photonic devices. Transparent crystalline materials can exhibit different kinds of optical nonlinearities which are associated with a nonlinear polarization. The choice of the most suitable crystal material for a given application is often far from trivial; it should involve the consideration of many aspects. A high nonlinearity for frequency conversion of ultra-short pulses does not help if the interaction length is strongly limited by a large group velocity mismatch and the low damage threshold limits the applicable optical intensities. Also, it can be highly desirable to use a crystal material which can be critically phasematched at room temperature. Among the different types of nonlinear crystals, metal halides and tartrates have attracted due to their importance in photonics. Metal halides like lead halides have drawn attention because they exhibit interesting features from the stand point of the electron-lattice interaction .These materials are important for their luminescent properties. Tartrate single crystals show many interesting physical properties such as ferroelectric, piezoelectric, dielectric and optical characteristics. They are used for nonlinear optical devices based on their optical transmission characteristics. Among the several tartrate compounds, Strontium tartrate, Calcium tartrate and Cadmium tartrate have received greater attention on account of their ferroelectric, nonlinear optical and spectral characteristics. The present thesis reports the linear and nonlinear aspects of these crystals and their potential applications in the field of photonics. |
| URI: | http://dyuthi.cusat.ac.in/purl/5062 |
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| Dyuthi-T 2127.pdf | (20.79Mb) |
| Abstract: | The thesis entitled “Photovoltaic and nonlinear optical studies of a few Donor-π-Acceptor molecules with s-triazine core” embodies the results of the investigations carried out to study unsymmetrically substituted s-Triazine cored starburst donor – acceptor systems with a bipodal acceptor/anchoring group design. The thesis opens with a review on the application of organic donor-acceptor systems in photovoltaics with special emphasis on applications in dye sensitised solar cells. The review also briefly discusses the application of such systems in the development of nonlinear optical materials.The unique structure of s-triazine do not permit direct coupling between the donor and acceptor moieties and this has been used as an effective tool for tuning HOMO and LUMO energy levels of such donor acceptor molecules. The effect of nature of the -bridge and the acceptor groups on the photovoltaic properties was studied and the results are presented in chapters 2, 3 and 4. Among the three types of -bridges studied, thiophene served as the best in terms of improving absorption spectral properties. Thiophene bridged dyes (DTT-CYA, DTT-RHA, DTT-BA and DTT-TBA) showed better coverage of the solar spectrum. Photovoltaic properties of these dyes were studied by constructing sandwhich model dye sensitized solar cells with nanocryasalline thin film of TiO2 on FTO coated with the respective dye as the photoanode, I-/I3- and Br-/Br3- as the redox couple/electrolyte and a platinized FTO as the cathode. The cell parameters and the photoconversion efficiency calculated show that the thiophene bridged dyes when used with Br-/Br3- as the redox couple/electrolyte have the optimal performance |
| URI: | http://dyuthi.cusat.ac.in/purl/5169 |
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| Dyuthi-T2203.pdf | (6.127Mb) |
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