【作者】 孔德贵；

【导师】 宋瑛林； 叶红安；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2010， 博士

【摘要】 随着激光技术的不断发展,超短激光脉冲被用于很多领域。在非线性光学方面,超短激光脉冲因其高的峰值强度和良好的时间分辨本领广泛用于研究各种材料的非线性光学性质。简单液体、金属酞菁及半导体材料三种典型材料在非线性光学研究领域具有巨大的潜在应用价值。通过研究简单液体分子在超短脉冲作用下的非线性光学特性使人们了解到了超短激光脉冲与简单液体分子相互作用时的微观机制,探索简单液体分子中电子、分子内运动及分子间运动等动力学过程。通过研究金属酞菁材料及半导体材料在超短脉冲作用下的非线性光学特性为其在实际应用中提供理论基础,同时也指导材料的合成。本文用飞秒激光脉冲通过Z-scan技术、光学克尔效应技术和泵浦探测技术研究了二硫化碳、二甲基亚砜、金属酞菁ZnPc（OBu）₆（NCS）及ZnSe晶体的非线性光学特性,并对实验结果进行解释。取得的主要创新成果如下:在低光强作用下,CS₂的光学非线性仅来源于三阶非线性效应,当光强增大到某一阈值时,三阶非线性效应和五阶非线性效应将同时出现。通过在不同光强下的Z-scan实验我们获得了三阶非线性折射率、五阶非线性折射率以及出现五阶效应的阈值。在800 nm波长下CS₂表现为三光子吸收,拟合实验结果获得了三光子吸收系数。CS₂在130 fs半高全宽激光脉冲作用下非线性响应包括寿命为160 fs的快弛豫成分和寿命为1.6 ps的慢弛豫成分。在400 nm波长作用下CS₂的非线性吸收来源于双光子吸收及其诱导的激发态吸收。通过理论拟合实验结果得到了CS₂的双光子吸收系数、激发态吸收截面以及激发态寿命。二甲基亚砜（DMSO）在130 fs半高全宽激光脉宽作用下的非线性响应几乎完全来自于电子的贡献,分子内运动和分子间运动的贡献可以忽略。用CS₂作为参考样品,测量得到了DMSO的三阶非线性极化率幅值约为CS₂的四分之一,而且主要来自于非线性折射的贡献,即三阶非线性极化率的实部。基于DMSO在超短脉冲作用下的瞬时响应,可以用DMSO作为非线性介质通过光学克尔效应方法测量超短激光脉冲宽度。通过自相关仪及光谱分析我们证明了在800 nm波长和400 nm波长下的测量结果是准确可以信的。用DMSO作为非线性介质通过光学克尔效应方法测量超短激光脉冲宽度其优点是适用的光谱范围宽,而且超短激光脉冲在DMSO中传输产生的群速色散非常小。金属酞菁ZnPc（OBu）₆（NCS）在超短脉冲作用下表现为饱和吸收和自聚焦效应。该分子在超短脉冲下的响应包括三部分贡献:电子的瞬时响应、一个快的弛豫成分和一个慢的弛豫成分。通过三能级模型和泵浦探测实验,我们证明了快的弛豫成分是来自高激发态上粒子的贡献,高激发态上的粒子寿命为850 fs;慢的弛豫成分来自低激发态粒子的贡献,低激发态上的粒子寿命为几个皮秒。金属酞菁ZnPc（OBu）₆（NCS）具有大的二阶超极化率,其幅值比C₆₀分子高三个数量级。在130 fs脉宽800 nm波长脉冲的作用下,ZnSe晶体的非线性折射来自于束缚电子的自聚焦效应;非线性吸收主要来自于束缚电子引起的带间的双光子吸收及双光子吸收诱导的导带内电子的单光子吸收,但是导带内电子的单光子吸收相比较于束缚电子的双光子吸收小很多。通过泵浦探测实验我们测得ZnSe晶体中通过双光子吸收跃迁到导带低能态上的粒子弛豫到导带底的时间为250 fs。因此,通过Z-scan技术测量得到的ZnSe晶体的非线性吸收和折射不包含载流子的贡献,完全来自于束缚电子的作用。更多还原

【Abstract】 With the development of laser technique, the ultrashort laser pulses are used in many fields. In the field of nonlinear optics, ultrashort pulses are used to investigate the nonlinear optical properties of many materials with their high peak intensity and good time resolved ability. The three typical materials of simple liquids, phthalocyanine and semiconductor have potential value in the respect of optical nonlinear application and investigation. The micromechanism of ineraction of ultrashort pulses with sample liquids can be analyzed by the investigation of response of simple liquid under the action of untrashort pulses. The electric movement, the intra-molecule movement and the inter-molecule movement can be explored in simple liquid. The investigation of nonlinear optical properties of phthalocyanine and semiconductor are helpful for guiding the synthesis of phthalocyanine and the application of semiconductor. In the paper, the nonlinear optical properties of CS₂, DMSO, phthalocyanine ZnPc（OBu）₆（NCS）, and ZnSe crystal are investigated by Z-scan, optical Kerr effect and pump-probe technique with 130 fs pulses. The experimental results are anslysised and explained. The following are innovative results obtained by us.The nonlinear optical effects of CS₂ come from the third order nonlinear effect under low incident intensity. The third order and fifth order effects are appeared simultaneously when the incident intensity is larger than some threshold value. We get the third order nonlinear refraction index, the fifth order nonlinear refraction index and the threshold value for emergence of fifth order nonlinear effects. The nonlinear abosorption of CS₂ is the three photon absorption at 800 nm wavelength. The three photon absorption coefficient is obtained by theoretical fitting the experimental results. The responses of CS₂, under the action of ultrashort pulses, include the fast decay component with lifetime of 160 fs and the slow decay component with lifetime of 1.6 ps. At 400 nm wavelength, the nonlinear absorption of CS₂ includes the two photon absorption and the excited state absorption induced by two photon absorption. The two photon absorption coefficient, the excited absorption cross section and the lifetime of excited state of CS₂ are obtained. The nonlinear response of DMSO is instantaneous under the action of 130 fs pulses, which comes from the electric movement. The responses of intra-molecule and inter-molecule movement can be neglected. The measured third-order nonlinear susceptibility of DMSO is about one-quarter of that of CS₂ with the CS₂ as reference by optical kerr effect experiment. The nonlinear susceptibility of DMSO comes from the nonlinear refraction, namely the real part of third order susceptibility. Based on the instantaneous response of DMSO, DMSO can be used as nonlinear media for measurement of ultrashort pulse with optical kerr effect technique. The measured pulse width with DMSO as nonlinear media is accurate, which is certified by single shot autocorrelator and spectrum analyse. The advangtages of using DMSO as nonlinear media are that DMSO can be used in a wide spectrum, and the little broaden of pulse when the pulse propagation of pulse in the media.Under the action of ultrashort pulses, the phthalocyanine ZnPc（OBu）₆（NCS） display the saturated absorption effect and the self-focusing effect. The responses of ZnPc（OBu）₆（NCS） include three parts: the instantaneous response of electric, the fast decay component and the slow decay component. By the pump probe experiment and the three-energy level analysis, we confirm that the fast decay component come from the contribution of population stayed on high excited state, which lifetime is 850 fs. The slow decay component come from the contribution of population stayed on low excited state, which lifetime is sevel picosecond. The second hyperpolarizability of ZnPc（OBu）₆（NCS） is larger three order than that of C60.The ZnSe crystal show self-focusing effect from the bound electron under the action of 130 fs pulse at 800 nm wave length. The nonlinear absorption of ZnSe are the two photon absorption of bound electron in value band and the signle photon absorption induced by the two photon absorption. The electron stayed on the low energy state excited by two photon absorption will absorp a single photon to be excited to the high energy state. But, the single photon absorption of bound electron stayed on the low energy state is less than that of two photo absorpin. The lifetime of electron stayed on low energy state in conduction band is 250 fs measured by pump probe experiment. The Z-scan experiment can not detect the absorption and refraction of carrier because the 250 fs lifetime is longer than pulse duration.更多还原