Nonlinear optical interactions of Co: ZnO nanoparticles in continuous and pulsed mode of operations

Nanoparticles of Co: ZnO were synthesized by a co-precipitation method and characterized structurally by XRD (wurtzite), FTIR and TEM (spherical, 6-13 nm). The oxidation state of the Co ions is confirmed as +2 from electron paramagnetic resonance (EPR). UV-Vis absorption spectra represent a complete transparency in the visible region. A zinc vacancy is identified by PL measurements at 410 and 465 nm. The intensity dependent third order nonlinearity is studied using two frequency doubled (532 nm) pumping sources namely nanosecond pulsed Nd: YAG and CW Nd: YAG lasers. The nonlinear optical coefficients are obtained by analyzing the z-scan curve on the basis of a thermal lensing model for CW excitation whereas two photon absorption (2PA) along with a absorption saturation process for ns excitation.