Studies on the Structural and Nonlinear Optical Characteristics of Metal Tungstate Nanostructures for Optical Limiting Applications

Abstract

This thesis presents a concise overview of third-order nonlinear optical newlinephenomena, focusing on mechanisms such as saturable absorption (SA), reverse newlinesaturable absorption (RSA), self-focusing, and self-defocusing, all of which play a newlinecrucial role in optical limiting applications. The Z-scan method enables effective newlineanalysis of nonlinear optical behaviors by providing a simple, so far powerful way to newlinemeasure both the nonlinear refractive index (nand#8322;) and the nonlinear absorption newlinecoefficient (and#946;) of materials. It achieves this through two configurations: closed-aperture newlineZ-scan and open-aperture Z-scan. In this research, the single-beam Z-scan technique is newlineemployed to investigate nonlinear absorption and refraction behaviors arising from the newlinenlo effects. newlineTo enhance the nonlinear optical properties of trivalent and divalent metal newlinetungstates, specifically Biand#8322;WOand#8326; and SrWOand#8324;, this research explores approaches like newlineelemental doping and the incorporation of MoSand#8322; nanocomposites. Pristine Biand#8322;WOand#8326;, as newlinewell as Biand#8322;WOand#8326; doped with La and Zn, were synthesized using the coprecipitation newlinemethod. La-doped Biand#8322;WOand#8326;, when tested with a continuous wave (CW) laser, newlinedemonstrated superior nonlinear properties, including higher nonlinear refraction and newlinegreater third-order nonlinear optical susceptibility compared to the undoped sample due newlineto the altered electronic environment. Zn-doped Biand#8322;WOand#8326;, examined under a pulsed laser, newlineexhibited pronounced RSA behavior and strong optical limiting capabilities. Zn doping newlineintroduces new energy levels and modifies the band structure of Biand#8322;WOand#8326;, resulting in newlineimproved visible-light absorption, higher nonlinear absorption, and enhanced optical newlinelimiting performance newline