Optically anisotropic media: New approaches to the dielectric function, singular axes, microcavity modes and Raman scattering intensities
Optically anisotropic media: New approaches to the dielectric function, singular axes, microcavity modes and Raman scattering intensities
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DOI：
10.1002/pssr.201600295
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发表时间：
2017-01
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影响因子：
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通讯作者：
M. Grundmann;C. Sturm;C. Kranert;S. Richter;R. Schmidt‐Grund;C. Deparis;J. Zúñiga-Pérez
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文献类型：
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作者：
M. Grundmann;C. Sturm;C. Kranert;S. Richter;R. Schmidt‐Grund;C. Deparis;J. Zúñiga-Pérez
通过双折射晶体（方解石）观察的拉曼散射强度作为入射和出射偏振的函数和拉曼张量的公式。七分之六的晶体系统是光学各向异性和双折射的。我们回顾了最近的见解，双轴晶体一般表现出四个奇异轴（或例外点），可以成对退化的特殊情况。平面各向异性微腔有效双轴系统进行了讨论，我们预测例外点，并证明实验部分合并的本征态。本文还讨论了各向异性晶体基于声子和电子共振的偶极振子的介电函数的一般形式。双折射对拉曼散射强度的影响历来被忽略或建模不正确。最近的单轴和双轴晶体理论解释了实验拉曼散射强度的激发没有自由参数的主方向，允许明确的确定的拉曼张量分量。上述观点得到了证明，特别是与当前技术上重要的材料GaN、ZnO（单轴）和β-Ga 2 O3（双轴）相关。
Formula for the Raman scattering intensity as a function of incoming and outgoing polarization and the Raman tensor viewed through birefringent crystal (calcite). Six out of seven crystal systems are optically anisotropic and birefringent. We review recent insight that biaxial crystals generally exhibit four singular axes (or exceptional points) which can pairwise degenerate for special cases. Planar anisotropic microcavities are discussed as effectively biaxial systems and we predict exceptional points and demonstrate experimentally partially coalesced eigenstates. Also the general form of the dielectric function of anisotropic crystals based on individual dipole oscillators for phonon and electronic resonance is discussed. The impact of birefringence on Raman scattering intensities has been historically either ignored or modeled incorrectly. A recent theory for uniaxial and biaxial crystals explains experimental Raman scattering intensities for excitation off the principal directions without free parameters, allowing the unambiguous determination of the Raman tensor components. The above points are demonstrated and relevant in particular for the currently technologically important materials GaN, ZnO (uniaxial) and β-Ga2O3 (biaxial).