Nano and Nanostructured Materials for Optical Applications

Nano and nanostructured materials offer unique physical and chemical properties that differ considerably from their bulk counterparts. For decades, due to their fascinating properties, they have been extensively explored and found to be beneficial in numerous applications. These materials are key components in many cutting-edge optic and photonic technologies, including photovoltaics, waveguides and sensors. In this dissertation, the uses of nano and nanostructured materials for optical applications are investigated in the context of optical limiting, three dimensional displays, and optical sensing. Nanomaterials with nonlinear optical responses are promising candidates for self-activating optical limiters. In the first part of this study, optical limiting properties of unexplored nanomaterials are investigated. A photoacoustic detection technique is developed as an alternative characterization method for studying optical nonlinearities. This was done with an indigenously developed setup for measuring the photoacoustic signals generated from samples excited with a pulse laser. A theoretical model for understanding the experimental observations is presented. In addition, the advantages of this newly developed technique over the existing methods are demonstrated. Blending optical sensitizers with photoconducting polymers and chromophores results in a polymer composite that is able to record a light grating. This composite can be used as recording media in 3D holographic display technology. Here, 2D nano materials, like graphenes, are used as optical sensitizers to improve the response time of a photorefractive polymer. The addition of graphenes to a PATPD/ECZ/7-DCST composite results in a three-fold enhancement in response time and therefore faster recording speed of the medium. The faster build-up time is attributed to better charge generation and mobility due to the presence of graphenes in the composite. Lastly, a facile nanofabrication technique is developed to produce metallic nanostructures with a tunable plasmonic response. The enhancement of the light-matter interactions due to these nanostructures in sensing an analyte is demonstrated

Enhanced optical limiting in nanosized mixed zinc ferrites

Optical limiting performance of zinc ferrite, nickel zinc ferrite, and copper zinc ferrite nanoparticles is investigated at 532 nm using 5 nanosecond laser pulses. Enhanced optical limiting is observed in the mixed zinc ferrites, which is attributed to the relative longevity of self-trapped charge transfer states. Samples exhibit absorption saturation followed by a rapid onset of optical limiting as the input fluence is increased. This is advantageous in applications where detector sensitivity should be retained at the maximum value until the input fluence approaches the detector damage regime. The Z-scan results are compared to those measured in C-60

Recent Advances in Optical Limiting Properties of Fluorinated Graphene Oxides

There is a substantial interest in finding materials with high nonlinear optical (NLO) properties of materials because of its attractive applications in optical limiting for safety protections. In an effort to develop highly performing optical limiting materials, recently we have found that fluorination of graphene oxides leads to improvement in their NLO properties

Coupling Enhancement And Giant Rabi-Splitting In Large Arrays Of Tunable Plexcitonic Substrates

Advances in active manipulation of light at the nanoscale are rapidly emerging with the concept of plexcitonic coupling at the interface between plasmonics nanostructures and excitonic molecules. In this work, we devise a simple fabrication scheme to produce and optimize large area tunable plasmonic substrates for strong plasmon-exciton interactions. By tuning the diameter of the nanoholes using a simple plasma etching process, we demonstrate the potential of our approach to deliver tunable plasmonic substrates. Thus, large enhancements of fluorescence and Raman scattering could be measured. Moreover, hybridized states appearing in the presence of excitonic molecules (RG6) give rise to anticrossing behaviors in extinction spectroscopy, a phenomenon also known as Rabi-splitting. The results demonstrate the great potential of our large nanofabricated arrays as plexcitonic substrates for numerous applications, including sensors, light harvesters, and all-optical switches

Simultaneous optical and photoacoustic measurement of nonlinear absorption

A measurement technique to perform optical Z-scan and photoacoustic Z-scan simultaneously called OPAZ-scan is demonstrated. It is found that the simultaneous measurement of the optical and photoacoustic Z-scan signals provides substantially better insight into the mechanism of optical nonlinearity. The system is able to identify mixed nonlinear processes within a mixture of nonlinear scattering species and nonlinear absorbers

Coupling Enhancement and Giant Rabi-Splitting in Large Arrays of Tunable Plexcitonic Substrates

Advances in active manipulation of light at the nanoscale are rapidly emerging with the concept of plexcitonic coupling at the interface between plasmonics nanostructures and excitonic molecules. In this work, we devise a simple fabrication scheme to produce and optimize large area tunable plasmonic substrates for strong plasmon-exciton interactions. By tuning the diameter of the nanoholes using a simple plasma etching process, we demonstrate the potential of our approach to deliver tunable plasmonic substrates. Thus, large enhancements of fluorescence and Raman scattering could be measured. Moreover, hybridized states appearing in the presence of excitonic molecules (RG6) give rise to anticrossing behaviors in extinction spectroscopy, a phenomenon also known as Rabi-splitting. The results demonstrate the great potential of our large nanofabricated arrays as plexcitonic substrates for numerous applications, including sensors, light harvesters, and all-optical switches

Evolution Of Nonlinear Optical Properties: From Gold Atomic Clusters To Plasmonic Nanocrystals

Atomic clusters of metals are an emerging class of extremely interesting materials occupying the intermediate size regime between atoms and nanoparticles. Here we report the nonlinear optical (NLO) characteristics of ultrasmall, atomically precise clusters of gold, which are smaller than the critical size for electronic energy quantization (∼2 nm). Our studies reveal remarkable features of the distinct evolution of the optical nonlinearity as the clusters progress in size from the nonplasmonic regime to the plasmonic regime. We ascertain that the smallest atomic clusters do not show saturable absorption at the surface plasmon wavelength of larger gold nanocrystals (\u3e2 nm). Consequently, the third-order optical nonlinearity in these ultrasmall gold clusters exhibits a significantly lower threshold for optical power limiting. This limiting efficiency, which is superior to that of plasmonic nanocrystals, is highly beneficial for optical limiting applications. © 2012 American Chemical Society

Applications Of Oxide Nanomaterials In Nonlinear Optics

Nonlinear optical effects are revealed when strong light fields interact with matter. It has been shown that nanomaterials exhibit properties which are very different from the bulk, and in many cases, the nonlinear optical (NLO) efficiency of nanomaterials is found to be higher in comparison. Recently there has been substantial interest in developing novel NLO media for various applications. Even though several organic as well as inorganic materials have been studied in this connection, only a limited number of NLO reports exist for oxide nanomaterials. Therefore, in this paper we present results of NLO measurements recently conducted in our laboratory in three different oxide nanosystems. It is found that oxide nanomaterials are generally robust, and exhibit good NLO efficiencies, which make them potential candidates for photonic and optoelectronic applications. © 2012 Materials Research Society

High-Throughput Of Polymer Derived Carbon Nanopillar Arrays For Enhanced Energy Storage Performance

Polyacrylonitrile (PAN) was printed into a nanostructured carbon nanopillar arrays using a quick, simple, and highly efficient method called spin-on nanoprinting (SNAP). The mold used to print PAN nanostructures could easily be reproduced via printing an inverse replica of carbon nanopillar arrays. The as-printed carbon nanopillar arrays were further prepared as supercapacitor electrodes. As a result, these nanostructured carbon electrodes display an order of magnitude enhancement in specific capacitance compared to non-nanostructured carbon electrodes

Recent Advances In Optical Limiting Properties Of Fluorinated Graphene Oxides

There is a substantial interest in finding materials with high nonlinear optical (NLO) properties of materials because of its attractive applications in optical limiting for safety protections. In an effort to develop highly performing optical limiting materials, recently we have found that fluorination of graphene oxides leads to improvement in their NLO properties. © 2013 SPIE