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Nonlinear optical properties of natural laccaic acid dye studied using Z-scan technique

- Zongo, S, Sanusi, Kayode, Britton, Jonathan, Mthunzi, P, Nyokong, Tebello, Maaza, M, Sahraoui, B

Authors: Zongo, S , Sanusi, Kayode , Britton, Jonathan , Mthunzi, P , Nyokong, Tebello , Maaza, M , Sahraoui, B
Date: 2015
Language: English
Type: Article
Identifier: vital:7261 , http://hdl.handle.net/10962/d1020270
Description: We have investigated the nonlinear optical properties, including the optical limiting behaviour for five different concentrations of laccaic acid dye in solution and a thin film obtained through doping in poly (methyl methacrylate) (PMMA) polymer. The experiments were performed by using single beam Z-scan technique at 532 nm with 10 ns, 10 Hz Nd:YAG laser pulses excitation. From the open-aperture Z-scan data, we derived that the laccaic dye samples exhibit strong two photon absorption (2PA). The nonlinear refractive index was determined through the closed aperture Z-scan data. The estimated absorption coefficient β2, nonlinear refractive index n2 and second order hyperpolarizability γ were found to be of the order of 10−10 m/W, 10−9 esu and 10−32 esu, respectively. The Z-scan study reveals that the natural laccaic acid dye emerges as a promising material for third order nonlinear optical devices application. , Original publication is available at http://dx.doi.org/10.1016/j.optmat.2015.04.031
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Date Issued: 2015

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Exploring the political geoecology of African Drainage Basins

- Rowntree, Kate

Authors: Rowntree, Kate
Date: 2008-04
Language: English
Type: Text
Identifier: vital:580 , http://hdl.handle.net/10962/d1018873 , Transcript of Inaugural lecture August 2007
Description: [From the text] Many people in Africa rely directly on their natural ecosystems for their livelihoods. A key driver of these ecosystems is water, which in Africa has a high spatial and temporal variability. Water comes from rainfall, but the availability of that water depends on the way that it is processed through the landscape unit known as a drainage basin. Drainage basins are the "home" of rivers; rivers which sustain ecosystems and their dependents (human society). Humans and ecosystems cannot live apart from one another, but the relationship can be exploitative and degrading, or harmonious and protective. Throughout history human activity has been subject to direct controls and indirect pressures subjected by the larger society, through political, economic and cultural forces that are often intertwined. Rivers are especially sensitive to the geography of this relationship. Being longitudinal ecosystems that transfer water and other materials from the source of the river to the oceans, activities in upstream areas have a direct impact on downstream areas. To explore these socio-ecological relationships within the context of an African drainage basin I have developed the concept of political geoecology that is explored in this address.
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Date Issued: 2008-04

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