title: Near-resonant high order nonlinear absorption of ZnO thin films.
abstract: Nonlinear optical absorption of ZnO thin film grown by the laser molecular beam epitaxy was investigated by the Z-scan method using a frequency-doubled femtosecond Ti:sapphire laser. Due to near-exciton resonance, an enormous enhancement of two photon absorption (TPA) is about 3000 cm/GW at 390 nm which is about 6.5 times larger than the previously reported at two-photon exciton resonance in near-IR regime and 710 times larger than that of ZnO bulk measured at 532 nm. Besides, the free-carrier absorption resulting from linear absorption and TPA becomes essential when the excitation approaches the exciton resonance.
authors.affiliation: Department of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, 1001 Tahsueh Rd., Hsinchu 30050, Taiwan.
authors.forename: Yun-Pei
authors.initials: YP
authors.lastname: Chan
authors.forename: Ja-Hon
authors.initials: JH
authors.lastname: Lin
authors.forename: Chih-Chang
authors.initials: CC
authors.lastname: Hsu
authors.forename: Wen-Feng
authors.initials: WF
authors.lastname: Hsieh