Investigation of thirdorder nonlinear optical and all-optical switching properties of some metalorganic materials

Abstract

Nonlinear optical (NLO) materials and their structural engineering have gained growing importance in the field of nonlinear optics due to their large diverse applications in optoelectronics and photonics. In our efforts to identify the structure dependent NLO properties, we have investigated three different classes of organometallic complexes, viz. (i) palladium complexes with Schiff base ligand containing triphenylphosphine, (ii) ruthenium complexes with 1,3 dithiole 2 thione- 4,5-dithiolate (dmit) and triphenylarsine/ triphenylphosphine ligands and (iii) ruthenium complexes of salen/salophene ligands. The solutions of these complexes were prepared by dissolving them into dimethylformamide (DMF) solvent. Solid films were formed by first dispersing the complexes in Polymethylmethacrylate (PMMA) solution and then spin-coating them on glass substrates. For linear optical characterization, UV-Vis absorption spectra and linear refractive indexes were determined for both solution and film form. Third-order nonlinear optical properties of the complexes were determined using Z-scan and Degenerate four wave mixing (DFWM) techniques with laser pulses of 7 ns at the wavelength of 532 nm. Using energy dependent transmission technique, optical power limiting performance of the complexes were studied. Further, all-optical switching behavior of the complexes were investigated using two color pump-probe technique. All complexes exhibit negative nonlinear refractive index (self-defocusing) and nonlinear absorption due to reverse saturable absorption (RSA) which is explained using five-level model. All the complexes investigated by us have shown good optical power limiting as well as all-optical switching behavior. This thesis provides an insight on the role of electron acceptor and electron donor substituent and the effect of !-conjugation and electron delocalization on third-order nonlinear optical properties of the metal-organic complexes. Further, the suitability of such materials for devices such as optical power limiters and all-optical switches is also discussed.