Photonic applications of functionalized gold nanorods: progress towards nonlinear metamaterials

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Montana State University - Bozeman, College of Letters & Science


Nonlinear processes are used to convert one color of laser light into another and are very useful to any research who needs multiple colors of light for basic research or commercial purposes. However, nonlinear processes are inherently very weak and require high input energy to utilize them. Using modeling, it was predicted that ordered arrays of gold nanorods (GNRs), acting as a metamaterial, could be used to fabricate a material that would exhibit field enhancement. Because nonlinear processes depend on the strength of the field in which they interact, enhancing the field strength while using the same amount of input power would make these processes much more efficient and useful. Progress towards these materials included the synthesis of GNRs and gold reactive polymers. These polymers were used to solubilize GNRs in organic solvents while also introducing attachment points for nonlinear chromophores. To study a material which resembled the one in our modeling predictions, flat gold and two dimensional arrays of gold nanopillars were functionalized with gold-reactive nonlinear organic chromophores and studied using sum frequency generation. It was found that flat gold samples functionalized with a nonlinear chromophore exhibited a tremendous SFG signal, but only in one input polarization configuration. However, gold nanopillar samples exhibited a significant SFG signal in both PPP and SSP polarization configurations. These data agree with our modeling results and indicate that the materials produced here have the potential to be used as a mirror-less optical parametric oscillator. Organic-soluble GNRs produced in this thesis were then used in an adjacent project to improve the efficiency of a diode-pumped solid state laser design. Nd:YAG lasers are routinely used to produced 1064 nm light by pumping at 808 nm with a semi-conductor diode laser. However, when 1064 nm light is reflected back into the laser cavity, a parasitic phenomenon called amplified spontaneous emission (ASE) occurs. ASE can be combatted by applying a material to the laser rod that absorbs at 1064 nm. GNRs were synthesized at a specific size to absorb at 1064 nm, solubilized in epoxy and applied to a Nd:YAG laser, increasing efficiency by almost two fold.




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