基于GaP晶体体相位光栅的太赫兹电磁波选频理论研究

发布时间：2018-07-21 21:13

【摘要】：近年来,太赫兹电磁波研究受到了国内外学术研究机构的高度重视,针对太赫兹波的产生和探测技术已取得突破性进展,与此同时,太赫兹材料检测技术也得到了广泛研究。相比太赫兹波产生和应用技术研究,其在大气通信方面的研究较少,因此太赫兹波选频研究能提高太赫兹波在通信工程领域的应用。本文在分析太赫兹波滤波研究的基础上,拟结合第一性原理方法,以利用超声波在GaP晶体内产生的体相位光栅进行太赫兹波反射选频理论研究。本文主要研究工作如下:(1)本文选用闪锌矿结构GaP晶体作为声光晶体进行0-7.5THz波段选频研究。利用第一性原理方法计算了 GaP晶体的光学参数、声学参数及晶格动力学参数;利用THz-TDS探测系统、声光效应测试系统和拉曼散射实验分别对GaP晶体(10mm×10mm×0.5mm)的太赫兹性质、声光效应和声子共振关系进行验证;给出了入射太赫兹波与超声波共线传输的改进型布拉格条件;分析了 GaP晶体耦合场量子色散方程,并计算出耦合场量子色散曲线。(2)根据超声波频率为常数时体相位光栅可视为超晶格结构,提出应用Kronig-panny模型分析体相位光栅的层状结构,得到了一维体相位光栅中含有带隙的电磁波传播的色散关系;结合TO声子耦合场量子色散关系、布拉格条件和声光耦合性质,研究了光学带隙频率和宽度随超声波频率和强度的变化关系。(3)根据体相位光栅的布拉格条件和声光耦合性质,依托TO声子耦合场量子色散方程和一维体相位光栅中电磁波传播的色散关系,首次提出了双原子立方晶体的改性TO声子耦合场量子色散方程;基于第一性原理计算结果计算了超声波频率在0-250MHz范围内改性耦合场量子色散曲线。(4)依据GaP晶体介电函数和改性耦合场量子色散方程,提出了改进型介电函数;计算了无体相位光栅作用下GaP晶体的反射谱,得到了剩余能量带及0-7.5THz频段反射率;通过分析改性TO声子耦合场量子色散关系及改进型介电函数,给出了 0级、-1级和-2级布拉格反射率方程。(5)通过分析GaP晶体布拉格反射率方程,并结合第一性原理计算结果,计算了超声波频率在0-200MHz频段内0级、-1级和-2级布拉格反射谱,研究了 0级、-1级和-2级布拉格反射谱峰宽度和反射率分别与超声波的频率和强度的关系;针对-2级反射谱在第二带隙位置出现的反射峰,本文给出了不含双声子反射的-2级反射率方程,并计算出反射谱。(6)得到了 THz波选频信号为0-7.5THz频段总布拉格反射谱。本文分别计算了超声波频率在0-200MHz和耦合强度在0.1-1meV范围的总布拉格反射谱。根据声光耦合强度和超声波强度的关系,得出结论:选频输出的太赫兹波频率和强度分别由超声波的频率和强度调制。
[Abstract]:In recent years, the research of terahertz electromagnetic wave has been attached great importance to by academic research institutions at home and abroad. The generation and detection technology of terahertz wave has made a breakthrough. At the same time, terahertz material detection technology has also been extensively studied. Compared with the research of terahertz wave generation and application technology, the study of terahertz wave frequency selection can improve the application of terahertz wave in the field of communication engineering. Based on the analysis of terahertz wave filtering and the first-principle method, the theoretical study of terahertz wave reflection frequency selection by using volume phase grating produced by ultrasonic wave in gap crystal is studied in this paper. The main work of this paper is as follows: (1) in this paper, the sphalerite structure gap crystal is used as acousto-optic crystal to study the frequency selection of 0-7.5 THz band. The optical parameters, acoustic parameters and lattice dynamics parameters of gap crystal were calculated by first-principle method, and the terahertz properties of gap crystal (10mm 脳 10mm 脳 0.5mm) were investigated by THz-TDS detection system, acousto-optic effect test system and Raman scattering experiment, respectively. The acousto-optic effect and phonon resonance are verified, the improved Bragg condition for collinear propagation of incident terahertz wave and ultrasonic wave is given, and the quantum dispersion equation of gap crystal coupling field is analyzed. The quantum dispersion curve of coupled field is calculated. (2) based on the fact that the volume phase grating can be regarded as a superlattice structure when the ultrasonic frequency is constant, a Kronig-panny model is proposed to analyze the layered structure of the volume phase grating. The dispersion relation of electromagnetic wave propagation with band gap in one-dimensional bulk phase grating is obtained, and the Bragg condition and acousto-optic coupling property are combined with the quantum dispersion relation of to phonon coupling field. The relationship between the frequency and width of the optical band gap and the ultrasonic frequency and intensity is studied. (3) according to the Bragg condition of the volume phase grating and the acousto-optic coupling property, Based on the quantum dispersion equation of to phonon coupling field and the dispersion relation of electromagnetic wave propagation in one-dimensional bulk phase grating, the modified to phonon coupling field quantum dispersion equation of diatomic cubic crystal is proposed for the first time. The quantum dispersion curve of the modified coupling field in the range of 0-250 MHz is calculated based on the results of first-principle calculation. (4) based on the dielectric function of gap crystal and the quantum dispersion equation of the modified coupling field, the modified dielectric function is proposed. The reflection spectrum of gap crystal under the action of bulk phase grating is calculated, and the residual energy band and reflectivity of 0-7.5 THz band are obtained, and the quantum dispersion relation of the modified to phonon coupling field and the improved dielectric function are analyzed. The Bragg reflectance equations of order 0 ~ (-1) and order 2 are given. (5) by analyzing the Bragg reflectance equation of gap crystal and combining with the results of first-principle calculation, the Bragg reflectance spectra of order 0 ~ (-1) and order 2 in the frequency range of 0-200 MHz are calculated. The relationship between the frequency and intensity of ultrasonic wave and the width and reflectivity of Bragg reflectance spectrum of order 0 and order 2 are studied respectively, and the reflection peaks of the second band gap of the reflection spectrum of order 2 are studied. In this paper, the reflectivity equation of order 2 without double phonon reflection is given, and the reflection spectrum is calculated. (6) the total Bragg reflectance spectrum of the selected frequency signal of THz wave is obtained in the frequency range of 0-7.5 THz. In this paper, the total Bragg reflectance spectra with ultrasonic frequency of 0-200MHz and coupling intensity of 0.1-1meV are calculated respectively. According to the relationship between the acousto-optic coupling intensity and the ultrasonic intensity, it is concluded that the frequency and intensity of the terahertz wave output from the selected frequency are modulated by the frequency and intensity of the ultrasonic wave respectively.
【学位授予单位】：西安理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O441.4

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