Near-resonant high order nonlinear absorption of ZnO thin films
Yun-Pei Chan1, Ja-Hon Lin, Chih-Chang Hsu
1Department of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, 1001 Tahsueh Rd., Hsinchu 30050, Taiwan.
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.
