ABSTRACT
Enhanced ultrafast optical nonlinearities of porous anodized aluminum oxide (AAO) nanostructures, well-known templates for quantum dots fabrication, have been investigated using the differential optical Kerr gate technique at 800 nm. The optical nonlinearity is strongly influenced by the pore number density, the pore size and the shape. Large values of the third-order nonlinear optical susceptibility (chi((3))) of the order of 10(-10)esu are measured. The nonlinear response time is faster than or comparable to the laser pulse width (90 fs) used. The origin and variation of such remarkable optical nonlinearities has been discussed by considering the nanoporous AAO as an effective medium and utilizing the extended Maxwell Garnet theory, and by considering the additional influence from pore diameter, pore shape and surface states.
ABSTRACT
The nonlinear absorption in nanostructured Ni-Ti alloys, fabricated by electrochemical deposition, was investigated at 532 and 1064 nm. The type of nonlinear absorption (saturable or reverse saturable absorption) was observed to depend on the laser intensity as well as on the nanoparticle size. The nanostructured Ni-Ti alloys comprising particle mean diameters of 20 and 30 nm exhibited large three-photon absorption (3PA coefficient approximately 10(6) cm(3)/GW(2)) and large two-photon absorption (2PA coefficient approximately 10(5) cm/GW) at 532 nm, respectively. The observed change over from reverse saturable absorption to saturable absorption at high peak intensities has qualitatively been analyzed by the excited-state theory of conduction electrons.
