Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/34648
Title: Optical Limiting properties of Novel Nanocomposites
Authors: VENKATESH MAMIDALA
Keywords: Nonlinear Optics, Femtosecond Laser Spectroscopy, Optical Limiting, Surface plasmon, Ag-Fe3O4 nanocomposites, Graphene Oxide-Organic hybrids
Issue Date: 3-Jan-2012
Source: VENKATESH MAMIDALA (2012-01-03). Optical Limiting properties of Novel Nanocomposites. ScholarBank@NUS Repository.
Abstract: The protection of optical sensors or human eyes from intense laser radiation is highly sought as the laser technology is growing tremendously with the development of highly powerful pulsed lasers. To meet such a demand, a vast amount of research efforts and advances have been made in search of optical limiting materials. This dissertation presents detailed optical limiting investigations performed on novel nanocomposites such as Ag-Fe3O4 nanocomposites and graphene oxide nanocomposites. First, we have investigated the effects of attached silver (Ag) particles on the nonlinear optical properties of Fe3O4 nanocubes using both experimental and theoretical approaches. Experimentally, using femtosecond Z-scan technique, we demonstrate the Ag-size dependence of both two-photon absorption (TPA) and nonlinear refractive index (NR) of Fe3O4 nanocubes. Discrete dipole approximation (DDA) modeling confirmed the observed enhancement. Examination of the optical limiting properties of these Ag-Fe3O4 nanocomposites for both femtosecond and nanosecond laser pulses, demonstrated that broad temporal optical limiting could be accomplished with low limiting threshold. The limiting threshold could be further reduced by increasing Ag particle size through plasmon enhancement. Secondly, with nanosecond laser pulses at 532 nm wavelength, we have measured the optical limiting properties of reduced graphene oxide-polymer composite solutions. Fluence-dependent transmittance measurements showed that the limiting threshold values of these reduced graphene oxide-polymer composites were better than that of carbon nanotubes. Nonlinear scattering experiments suggested that nonlinear scattering should play an important role in the observed optical limiting effects. Lastly, we have shown a simple strategy to enhance optical limiting responses in donor-acceptor complexes by utilizing ionic interactions between donor and acceptor materials. Transient absorption measurements of the donor-acceptor complexes confirmed that the major contributor to the enhanced optical limiting properties was the addition of energy transfer pathway, responsible for excited-state deactivation, in turn leading to enhanced nonlinear scattering. These findings strongly support a potential application of donor-acceptor complexes for all laser protection devices.
URI: http://scholarbank.nus.edu.sg/handle/10635/34648
Appears in Collections:Ph.D Theses (Open)

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