Femtosecond Degenerate Four-Wave-Mixing in ZnO Microcrystallite Thin Films

Transient third-order optical nonlinearity Χ⁽³⁾ of ZnO microcrystallite thin films is measured at various temperatures by using femtosecond degenerate four-wave-mixing. Room-temperature excitonic enhancement of Χ⁽³⁾ is observed. The magnitude of Χ⁽³⁾) ranges between 10^-4 to 10^-6 esu from 4.2K to room temperature. The measured Χ⁽³⁾response time ranging from 200 to 300fs is ultrafast for temperature down to 4.2K.