Third-order optical nonlinearity in ZnO microcrystallite thin films

We report the measurement of third-order optical nonlinearity (χ(3)) of ZnO microcrystallite thin films near the excitonic resonance at various temperatures using the femtosecond degenerate four-wave-mixing technique. The measured χ(3) response times are 270, 240, and 160 fs at 4.2 K, 77 K, and room temperature, respectively. The values of χ(3) range from 10−7 to 10−4 esu. The maximum values of χ(3) always correspond to the absorption peaks at different temperatures. Room-temperature excitonic enhancement of χ(3) is also observed.