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| Description: | International School of Photonics |
| URI: | http://dyuthi.cusat.ac.in/purl/5026 |
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| Dyuthi-2092.pdf | (10.46Mb) |
| Abstract: | The rapid developments in fields such as fibre optic communication engineering and integrated optical electronics have expanded the interest and have increased the expectations about guided wave optics, in which optical waveguides and optical fibres play a central role. The technology of guided wave photonics now plays a role in generating information (guided-wave sensors) and processing information (spectral analysis, analog-to-digital conversion and other optical communication schemes) in addition to its original application of transmitting information (fibre optic communication). Passive and active polymer devices have generated much research interest recently because of the versatility of the fabrication techniques and the potential applications in two important areas – short distant communication network and special functionality optical devices such as amplifiers, switches and sensors. Polymer optical waveguides and fibres are often designed to have large cores with 10-1000 micrometer diameter to facilitate easy connection and splicing. Large diameter polymer optical fibres being less fragile and vastly easier to work with than glass fibres, are attractive in sensing applications. Sensors using commercial plastic optical fibres are based on ideas already used in silica glass sensors, but exploiting the flexible and cost effective nature of the plastic optical fibre for harsh environments and throw-away sensors. In the field of Photonics, considerable attention is centering on the use of polymer waveguides and fibres, as they have a great potential to create all-optical devices. By attaching organic dyes to the polymer system we can incorporate a variety of optical functions. Organic dye doped polymer waveguides and fibres are potential candidates for solid state gain media. High power and high gain optical amplification in organic dye-doped polymer waveguide amplifier is possible due to extremely large emission cross sections of dyes. Also, an extensive choice of organic dye dopants is possible resulting in amplification covering a wide range in the visible region. |
| URI: | http://dyuthi.cusat.ac.in/purl/661 |
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| Dyuthi-T0329.pdf | (2.138Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/1106 |
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| Radhakrishnan P 1986.pdf | (1.269Mb) |
| Abstract: | Laser-induced damage is the principal limiting constraint in the design and operation of high-power laser systems used in fusion and other high-energy laser applications. Therefore, an understanding of the mechanisms which cause the radiation damage to the components employed in building a laser and a knowledge of the damage threshold of these materials are of great importance in designing a laser system and to operate it without appreciable degradation in performance. This thesis, even though covers three distinct problems for investigations using a dye Q-switched multimode Nd:glass laser operating at 1062 nm and emitting 25 ns (FWHM) pulses, lays its main thrust on damage threshold studies on thin films. Using the same glass laser two-photon excited fluorescence in rhodamine 6G and generation and characterisation of a carbon plasma have also been carried out. |
| Description: | Department of Physics, Cochin University Of Science And Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/3761 |
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| Dyuthi-T1723.pdf | (11.63Mb) |
| Abstract: | Laser-induced damage is the principal limiting constraint in the design and operation of high-power laser systems used in fusion and other high-energy laser applications. Therefore, an understanding of the mechanisms which cause the radiation damage to the components employed in building a laser and a knowledge of the damage threshold of these materials are of great importance in designing a laser system and to operate it without appreciable degradation in performance. This thesis, even though covers three distinct problems for investigations using a dye Q-switched multimode Nd:glass laser operating at 1062 nm and emitting 25 ns (FWHM) pulses, lays its main thrust on damage threshold studies on thin films. Using the same glass laser two-photon excited fluorescence in rhodamine 6G and generation and characterisation of a carbon plasma have also been carried out. The thesis is presented in seven chapters. |
| Description: | Department of Physics, Cochin university of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/3316 |
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| Dyuthi-T1315.pdf | (11.63Mb) |
| Abstract: | The spectral and nonlinear optical characteristics of nano ZnO and its composites are investigated. The fluorescence behaviour of nano colloids of ZnO has been studied as a function of the excitation wavelength and there is a red shift in emission peak with excitation wavelength. Apart from the observation of the reported ultra violet and green emissions, our results reveal that additional blue emissions at 420 nm and 490 nm are developed with increasing particle size. Systematic studies on nano ZnO have indicated the presence of luminescence due to excitonic emissions when excited with 255 nm as well as significant contribution from surface defect states when excited with 325 nm. In the weak confinement regime, the third-order optical susceptibility χ(3) increases with increasing particle size (R) and annealing temperature (T) and a R2 and T2.5 dependence of χ(3) is obtained for nano ZnO. ZnO nanocolloids exhibit induced absorption whereas the self assembled films of ZnO exhibit saturable absorption due to saturation of linear absorption of ZnO defect states and electronic effects. ZnO nanocomposites exhibit negative nonlinear index of refraction which can be attributed to two photon absorption followed by weak free carrier absorption. The increase of the third-order nonlinearity in the composites can be attributed to the enhancement of exciton oscillator strength. The nonlinear response of ZnO nanocomposites is wavelength dependent and switching from induced absorption to saturable absorption has been observed at resonant wavelengths. Such a change-over is related to the interplay of plasmon/exciton band bleach and optical limiting mechanisms. This study is important in identifying the spectral range and the composition over which the nonlinear material acts as an optical limiter. ZnO based nanocomposites are potential materials for enhanced and tunable light emission and for the development of nonlinear optical devices with a relatively small optical limiting threshold. |
| URI: | http://dyuthi.cusat.ac.in/jspui/handle/dyuthi/1674 |
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| Dyuthi-T0546.pdf | (2.426Mb) |
| Abstract: | We live in an Information age, which is marked by the onset of digital revolution during or after the latter half of the 20th century. In this era, we saw sweeping changes in digital computing and communication technology. We largely depend on electronics and photonics for hardware requirements to aid this technology. With the assistance of modern technology, electronic devices have become an indispensable tool in our everyday life. Inorganic semiconductor materials like silicon and gallium arsenide have been exploited for the on-growing demands of digital revolution. Fifty years of continuous research and technological advancements have pushed these materials to their theoretical efficiency limit. On the other hand, the rapid advancement in technology has created a huge electronic waste which pose a threat to the environment. The scarcity of inorganic materials such as gallium and indium is an alarming factor and it is estimated that these will run out completely in the next 20 years. The availability of new suitable materials is crucial for the development of semiconductor technology. With much promise of delivering low-cost and energy efficient materials, organic semiconductors such as conjugated polymers and small molecules have opened up new avenues for research. Despite the intense effort by scientists and researchers, the performance and stability of organic devices have taken a back seat. Therefore an immediate large-scale replacement of inorganic components by organic counterparts are not foreseen in the near future. Although research is underway to improve the performance of organic materials, it is important to constantly search for new materials.Nature is a big treasure-trove of successfully conducted experiments by natural selection. Inspired by its apparent simplicity and actual complexity, researchers look out for natural materials or synthetic materials mimicked from natural models, systems or elements. Bio-inspired photonics use natural design as their inspiration to solve human problems and channel these solutions in new directions. It is promising that natural and nature-inspired materials can achieve the ambitious goal of ‘green’ technology for sustainable future. |
| URI: | http://dyuthi.cusat.ac.in/purl/5156 |
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| Dyuthi-T2190.pdf | (8.356Mb) |
Now showing items 1-7 of 7
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