Fabrication and characterization of thin films and optical nanocomposites
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Aluminum nitride thin films were fabricated and characterized using Pulsed Laser Deposition with varying processing conditions in order to exploit the feasibility as an encapsulating matrix for nonlinear nanocomposites. We have studied the dependence of optical properties, structural properties and their correlations for these AlN films. Low optical absorption, textured polycrystalline AlN films can be produced by PLD on sapphire substrates using a background nitrogen pressure of 4.5×10-4 Torr at 99.9% purity. In order to accurately extract optical properties of non-uniform films, we have developed and successfully applied the Optimum Parameter Extraction (OPE) numerical method. The OPE method can accommodate films with two-dimensional thickness variation. Previous methods rendered significant errors in values of refractive index and film thickness when applied to absorbing and wedged films. GaN nanocomposite coated with AlN film and silver nanocomposite coated with NdAlO3 were successfully synthesized and their nonlinear optical properties were characterized by ultrafast laser. The enhancement of THG in GaN nanocomposite did not occur because the LAM process would change crystalline GaN feedstock into semi-amorphous GaN nanoparticles. The THG signal was enhanced in bare silver nanopaprticles due to the plasmon resonance. On the contrary, in the case of Ag NPs coated with NdAlO3 the THG intensity was decreased by 40% at intermediate fields because the plasmon resonance wavelength was redshifted and moved off the twophoton resonance wavelength of the laser.