硅酸镓镧晶体光电性能及应用研究

【作者】 祁海峰；

【导师】 魏爱俭；

【作者基本信息】 山东大学 ， 光学工程， 2005， 硕士

【摘要】 从20世纪80年代首次报道至今,硅酸镓镧(La₃Ga₅SiO₁₄,简称LGS)晶体的研究一直为人们所关注。最初,LGS被作为激光晶体研究,自从有关LGS单晶振动具有零温度系数的报道之后,对LGS的压电性能以及声体波（BAW,bulk acoustic wave）、声表面波（SAW,surface acoustic wave）性能的研究成为热点。LGS具有比石英大2～3倍的机电耦合系数,与石英相当的温度稳定性,BAW、SAW传播速度低,从室温到熔点（1470℃）都没有相变。诸多特性使得LGS成为压电领域广泛关注的对象。就像石英一样,LGS也是一种用途广泛的材料。LGS具有适中的电光性质:稳定的物理化学性质,可调的半波电压,中等的损伤阈值,成熟的生长技术。因此,LGS在光学、电光领域的应用前景又引起了研究者的重视,用其制作的调Q开关被用于中等功率激光器中实现稳定输出。本文利用多种光学手段,对LGS的光学性质和电光性质进行了研究,系统的描述了LGS的这种多功能材料的光电性能情况;并从理论上分析了LGS的BAW和SAW传播特性,以此可以为LGS的声光研究提供一定的理论指导。 Ⅰ.采用反射式椭圆偏振光谱技术,在可见光区无损伤的测量了小尺寸LGS晶体样品的折射率,拟合了Sellmeier色散方程。 Ⅱ.采用平行偏振光干涉,通过记录干涉光谱,直接计算了LGS晶体的双折射率。n_e-n_o≈0.01,小的双折射使LGS无法实现正单轴晶的第一、第二类角度位相匹配谐波倍频。 Ⅲ.采用平行偏振光干涉,测量LGS晶体的旋光,拟合了Boltzmann旋光色散方程。LGS旋光小于石英,样品为右旋晶。 Ⅳ.由于旋光的存在,LGS电光现象不同于常见的磷酸二氘钾（KD₂PO₄,DKDP）电光晶体。经过对LGS旋转,在一条光路上用DKDP补偿位相差,测量了小长宽比LGS晶体样品的线性电光系数γ11,并将LGS用于对声频、超声频信号的线性调制。 Ⅴ.从理论上分析计算了LGS声体波传播特性,画出BAW慢度曲线。更多还原

【Abstract】 Since the first report of langasite (La₃Ga₅SiO₁₄, LGS) in 1980s, the study on LGS has been constantly paid attention to by researchers. At first, LGS was mainly studied as laser crystal. After the discovery of zero temperature dependence cut of LGS single crystal, the studies on its piezoelectric performance, bulk acoustic wave and surface acoustic wave performances became the focus of researches. LGS crystal exhibits many advantages for the above application fields, such as large electromechanical coupling factors which are as high as twice to three times of those of quartz （α-SiO₂） while the same temperature properties, lower velocities of bulk acoustic and surface acoustic waves compared with those of quartz, and no phase transitions from room-temperature to the melting point （1470℃）. All the advantages make LGS a very attractive subject in piezoelectric field. Like quartz, LGS is also a kind of material with multiple usages. It has proper electro-optic properties, such as stable physical and chemical properties, adjustable half-wave voltage, and medium damage threshold. Therefore, the prospect of LGS applied in optical and electro-optic fields attracts the attention of researchers. The electro-optic Q switch fabricated with LGS was used in medium power laser cavity, and the stable output was obtained. In this dissertation, the optical and electro-optic properties of LGS were studied by different optical techniques, and the photoelectric performance of LGS crystal was systematically described. Also the propagating characteristics of BAW and SAW in LGS were theoretically analyzed which might provide some theoretical guidance for study on its acousto-optic performance. The main content of this dissertation is as follows:Ⅰ.The refractive indices of LGS in visible light region were measured without impairment by the reflection ellipsometry method. The refractive dispersion curve of LGS was fitted to Sellmeier’s equation.Ⅱ. According to interfering theory of parallel polarized light, the birefringence of LGS was calculated through recording the interfering spectrum. The result was n_e-n₀≈0.01.The birefringence was so little that the phase-matched optical second harmonic generation for LGS is impossible.IIl.The optical activity of LGS was investigated by the same parallel interferometric method as above. The specific rotation dispersion was fitted to Boltzmann’s equation. The optical rotation of LGS is relatively small compared with that of quartz.IV.The electro-optic phenomena were investigated, which was not in common with that of KD2PO4 （DKDP） for the optical activity. The linear electro-optic coefficient yn of LGS sample with a small ratio of length to width was conveniently determined by placing one DKDP electro- optic crystal in the unique beam path to compensate the phase difference induced by LGS. Thereafter, the experiment of linear modulation for the voltage signal in sonic and ultrasonic frequency by LGS crystal was carried out.V.Theoretically analysis on the propagating characteristics of BAW in LGS crystal was finished. The slowness curves of BAW in different planes of LGS were plotted. The propagating characteristics of SAW were also described.更多还原