Bound-electronic and free-carrier optical nonlinearities and relaxation of two-photon-excited free carriers in ZnO have been investigated by use of a single-beam Z-scan technique at 532 nm. Under pulsed radiation of 25-ps duration, the two-photon absorption coefficient, the bound-electron nonlinear refractive index, and the change in the refractive index due to the two-photon generation of an electron–hole pair are determined to be 4.2±0.9 cm/GW, −(0.9±0.3)×10<sup>−14</sup> cm<sup>2</sup>/W, and −(1.1±0.3)×10<sup>−21</sup> cm<sup>3</sup>, respectively. With these values in the Z scans conducted with 7-ns laser pulses, the carrier recombination time and the free-carrier absorption cross section are extracted as 2.8±0.6 ns and (6.5±0.9)×10<sup>−18</sup> cm<sup>2</sup>, respectively.
© 1997 Optical Society of America
X. J. Zhang, W. Ji, and S. H. Tang, "Determination of optical nonlinearities and carrier lifetime in ZnO," J. Opt. Soc. Am. B 14, 1951-1955 (1997)