磁気－プラズモンナノ構造における光－物質相互作用

相干准粒子（如磁振子或声子）的激发和探测在过去的几十年里引起了相当大的科学兴趣，因为它可以用来研究各种材料的动力学性质。在这几类材料中，石榴石属于一个重要的类别，因为它可以实际开发用于红外区的光通信，设计微波滤波器和制造高频磁光调制器。在本研究中，我们利用飞秒泵浦-探测技术来激发石榴石中的相干准粒子。结果表明，线偏振泵浦激发出频率为4.2THz的准粒子。重要的是，4.2 THz模式的频率没有表现出任何明显的温度变化，这表明4.2 THz模式与声子的激发有关，而不是与磁振子的激发有关。一个唯象的基于量子力学的理论表明，从高频Eg声子模式的振荡被激发。线偏振抽运的选择性激发和圆偏振探针的探测证实了脉冲受激拉曼散射（ISRS）是驱动石榴石中相干声子的原因。从ISRS测量得到的实验结果表明惊人的协议与自发拉曼数据的石榴石考虑声子模式的对称性和相应的激发和检测选择规则。

Excitation and detection of coherent quasiparticles, e.g. magnons or phonons have been attracted considerable scientific interest in the last few decades because it can be exploited to investigate the dynamical properties of wide range of materials. Among the several classes of materials, garnet belongs to an important class because it can be practically exploited for optical communication in IR regime, designing microwave filters and fabricating high frequency magneto-optical modulators. In this study, we employed femtosecond pump-probe technique to excite the coherent quasiparticle in the garnet. Our result indicates that linearly polarized pump excites the quasiparticle of frequency 4.2 THz. Importantly, 4.2 THz mode does not exhibit any noticeable change in the frequency against the temperature variation which reveals that the 4.2 THz mode is associated with the excitation of phonons, instead of magnons. A phenomenological symmetry-based theory reveals that oscillations from high frequency Eg phonon modes are excited. Selective excitation by linearly polarized pump and detection by circularly polarized probe confirms that impulsive stimulated Raman scattering (ISRS) is responsible for driving the coherent phonons in the garnet. Experimental results obtained from ISRS measurements show striking agreements with spontaneous Raman data of the garnet by taking into account the symmetry of phonon modes and corresponding excitation and detection selection rules.