Particle size-dependent giant nonlinear absorption in nanostructured Ni-Ti alloys

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 similar to 10(6) cm(3)/GW(2)) and large two-photon absorption (2PA coefficient similar to 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. (C) 2008 Optical Society of America.