GaN晶体在飞秒紫外波段激发下的可变非线性吸收效应和光动力学过程研究

发布时间：2018-04-25 06:06

本文选题：GaN薄膜 + 自由载流子吸收　；参考：《光谱学与光谱分析》2017年12期

【摘要】：采用Z扫描和泵浦-探测技术研究了GaN薄膜在370nm时的非线性光学效应和非线性光动力学过程。首先,基于GaN薄膜的透射光谱,结合线性光学理论分析得到了其在370nm的线性折射率n_0、线性吸收系数α_0、光学带隙E_g等线性光学性质。采用飞秒激光Z扫描技术,得到了不同光强激发下的Z扫描实验响应结果,结合非线性光学理论提取出GaN薄膜可变的光学非线性吸收效应。在激发光子能量接近GaN带隙情况下,低光强时材料表现为饱和吸收而高光强时为反饱和吸收,这是因为低光强下单光子吸收占主导而高光强下以单光子感应自由载流子吸收为主。闭孔Z扫描测量得到了GaN薄膜的三阶非线性折射系数为n_2=-(1.0±0.1)×10~(-3) cm~2·GW-1,它几乎比传统非线性介质的高出一个数量级。为了探究上述非线性过程的动力学弛豫时间以及进一步探究GaN薄膜非线性光动力学过程的深层物理机制,采用了交叉偏振飞秒退相泵浦探测技术观察GaN薄膜的光激发载流子动力学弛豫过程。实验结果表明,在低光强下,饱和吸收效应来源于瞬态单光子吸收,高光强下单光子感应自由载流子吸收为非瞬态光动力学过程,其自由载流子弛豫时间约为17ps。该工作将为GaN薄膜在紫外非线性纳米器件应用以及GaN薄膜非线性过程的机制分析理解提供新的思路。
[Abstract]:The nonlinear optical effects and nonlinear photodynamic processes of GaN thin films during 370nm were studied by Z scan and pump detection techniques. Firstly, based on the transmission spectra of GaN thin films, the linear optical properties such as the linear refractive index n _ s _ 0, the linear absorption coefficient 伪 _ 0 and the optical band gap E _ g of the GaN thin films are obtained by combining with the linear optical theory. By using femtosecond laser Z scan technique, the experimental results of Z scan excited by different light intensities are obtained, and the variable nonlinear absorption effect of GaN thin films is extracted by combining with nonlinear optics theory. When the excited photon energy is close to the GaN band gap, the material exhibits saturated absorption at low light intensity and reverse saturation absorption at high light intensity. This is because the order photon absorption is dominated by low light intensity and the single photon induced free carrier absorption is dominant at high light intensity. The third-order nonlinear refraction coefficient of GaN thin film is obtained by closed cell Z scan measurement. The coefficient of the third order nonlinear refraction is ns _ 2n ~ (-1 卤1.0 卤0.1) 脳 10 ~ (-1) cm~2 GW-1, which is almost an order of magnitude higher than that of the traditional nonlinear medium. In order to explore the dynamic relaxation time of the above nonlinear process and the deep physical mechanism of the nonlinear photodynamic process of GaN thin films, Cross-polarization femtosecond dephase-pumped detection technique was used to observe the dynamic relaxation process of photoexcited carriers in GaN films. The experimental results show that at low light intensity, the saturated absorption is due to transient single-photon absorption, and the order photon induced free carrier absorption is a non-transient photodynamic process with a relaxation time of about 17ps. This work will provide a new idea for the application of GaN thin films in UV nonlinear nanodevices and for the mechanism analysis and understanding of the nonlinear process of GaN thin films.
【作者单位】：中南大学物理与电子学院超微结构与超快过程湖南省重点实验室;东南大学电子科学与工程学院先进光子学中心;
【基金】：国家自然科学基金项目(61222406,11174371,11474052) 湖南省自然科学基金项目(12JJ1001) 教育部博士学科点专项科研基金项目(20110162120072);教育部新世纪优秀人才支持计划(NCET-11-0512)资助
【分类号】：O484.41

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