| 研究実績の概要 |
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.
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