Two-photon pumped random laser in nanocrystalline ZnO

Thin film of ZnO nanoparticles with dimension of about 5 - 10 nm were fabricated by the pulsed laser ablation method. By using a femtosecond laser beam at 700 nm to pump micrometer-thick films the authors observed two-photon-induced lasing at 385 nm . Experimentally obtained dependence of the threshold on the excitation spot radius r 0 is closer to ( 1 ∕ r 0 2 ) than to ( 1 ∕ r 0 ) , thus suggesting efficiency of the feedback by scattering-random lasing. The experimental data on nonlinear transmission of the film at the wavelength of pumping are presented.