Abstract-Excitation of multiple phonon modes in copper metaborate CuB 2 O 4 via nonresonant impulsive stimulated Raman scattering

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 CuB${}_2$O${}_4$ 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.