Z掃瞄量測氧化鋅薄膜之非線性光學效應

Abstract

利用飛秒超短脈衝鈦藍寶石雷射從事變化強度Z-掃瞄量測技術研究Laser-MBE成長之氧化鋅薄膜。在 742nm，其雙光子吸收係數β＝1905cm/GW，三階非線性折射係數γ=2.21□10-11 cm2/W以及五階非線性折射係數σr=4.51□10-20 cm3，比理論預測大了許多。並經由變化波長的結果顯示出，非線性吸收及折射增強的原因是由於入射光的能量接近雙光子共振能帶。而激子共振的現象對非線性折射有很大的貢獻，這是由於自由激子受到強光的影響而產生自由載子對非線性折射造成很大的影響。

By utilizing femtosecond Kerr Mode-Locked Ti:sapphire laser as Z-scan light source, we have studied intensity dependent nonlinear refractive index of the ZnO thin film growth by Laser-MBE epitaxy. The two photon absorption coefficient β=1905 cm/GW, the third order nonlinear refractive index γ= 2.11□10-11cm2/W and the fifth order nonlinear refractive index σr=4.51□10-20cm3 with 748nm-wavelength of incident laser. Compared with two-band model, γ is 2000 times larger than theoretical value this is owing to near two-photon resonance. Results of β dependent with incident wavelength reveal this two-photon resonance behavior and results of σr dependent with incident wavelength show that free-carrier is induced by free-excitons under a intense light source pumping. The results of γ dependent with incident wavelength also show two-photon resonance behavior and excitonic enhancement.