Laser induced thermal lensing effects in Ag_xCu_(1-x)S-PMMA thin films

Abstract We report enhancement in the third order nonlinear optical (NLO) properties of Ag x Cu (1-x) S-PMMA thin films induced by He-Ne laser. This thermally stimulated increment in NLO properties has been obtained by synthesizing l-alanine capped pure and Ag doped CuS nanoparticles (NPs) by simple co-precipitation method. Colloidal suspension of NPs with polymethyl methacrylate (PMMA) have been spin coated on glass substrate to obtain thin films. Highly pure hexagonal covellite CuS nano-phase was confirmed by X-ray diffraction and elemental compositions were identified using energy dispersive X-ray spectroscopy (EDS). CuS NPs with near spherical shape having uniform morphology with estimated particle size of 10-20 nm have been witnessed using high resolution transmission electron microscopy (HR-TEM). Absorption spectra show broad absorption peaks in the wavelength range 610-675nm due to local surface plasmon resonance (LSPR) which shift in lower wavelength region with increase in the Ag concentration. Open and closed aperture z-scan technique was employed to determine NLO coefficients of thin films. A very large value of n2 and β were reported for 3wt% Ag doped CuS-PMMA thin films showing strong self-defocussing effect and reverse saturable absorption proving potential candidate for NLO applications such as optical limiting, all optical switching devices, etc.