The ultrafast switching of magnetization in multiferroic materials by a femtosecond laser could provide various advantages in photonics and magnonics. An efficient approach to control the light matter interaction is the modulation of ultrafast coherent magnons and phonons in the high frequency range. Spontaneous Raman and infrared spectra reveal the excitation of magnons and optical phonons in multiferroic BiFeO3 in the sub few terahertz range. However, coherent control of such quasiparticles has not been achieved yet. In this study, we demonstrate that linearly polarized laser pulses simultaneously excite coherent magnons out of plane and in plane cyclone modes and optical phonon E mode in BiFeO3. Experimental results in conjugation with phenomenological theory, by considering three uniformly distributed magnetic domains reveal that impulsive stimulated Raman scattering is responsible for the generation of coherent magnons and phonons in BiFeO3. The observation of these terahertz magnon and optical phonon modes paves the way for the development of ultrafast magneto electro optical devices.
Kotaro Imasaka, Roman V. Pisarev, Leonard N. Bezmaternykh, Tsutomu Shimura, Alexandra M. Kalashnikova, and Takuya Satoh
https://journals.aps.org/prb/accepted/62070Od9Oae1523411b61fc481644a9591593bae3
The excitation of four coherent phonon modes of different symmetries are realized in copper metaborate CuB2O4 via impulsive stimulated Raman scattering (ISRS). The phonons are detected by monitoring changes in the linear optical birefringence using the polarimetric detection (PD) technique. We compare the results of the ISRS-PD experiment to the polarized spontaneous Raman scattering spectra. We show that agreement between the two sets of data obtained by these allied techniques in a wide phonon frequency range of 4--14\,THz can be achieved by taking into account the symmetry of the phonon modes and corresponding excitation and detection selection rules. It is also important to account for the difference between incoherent and coherent phonons in terms of their contributions to the Raman scattering process. This comparative analysis highlights the importance of the ratio between the frequency of a particular mode, and the pump and probe spectral widths. We analytically demonstrate that the pump and probe pulse durations of 90 and 50 fs, respectively, used in our experiments limit the highest frequency of the excited and detected coherent phonon modes to 12 THz, and define their relative amplitudes.
We employed a femtosecond pump-probe technique to investigate the dynamics of coherent phonons in iron garnet. A phenomenological symmetry-based theory reveals that oscillations of the terahertz Eg mode are excited. Selective excitation by a linearly polarized pump and detection by a circularly polarized probe confirm that impulsive stimulated Raman scattering (ISRS) is the driving force for the coherent phonons. Experimental results obtained from ISRS measurements show an excellent agreement with spontaneous Raman spectroscopy data, analyzed by considering the symmetry of the phonon modes and corresponding excitation and detection selection rules.
