Third-order optical nonlinearity in ZnO microcrystallite thin films

We report the measurement of third-order optical nonlinearity (chi((3))) of ZnO microcrystallite thin films near the excitonic resonance at various te mperatures using the femtosecond degenerate four-wave-mixing technique. The measured chi((3)) response times are 270, 240, and 160 fs at 4.2 K, 77 K, and room temperature, respectively. The values of chi((3)) range from 10(-7 ) to 10(-4) esu. The maximum values of chi((3)) always correspond to the ab sorption peaks at different temperatures. Room-temperature excitonic enhanc ement of chi((3)) is also observed. (C) 1999 American Institute of Physics. [S0003-6951(99)05047-0].