Fig. 2: Comparison of phonon frequencies at 0° and 90° laser polarizations.
From: Strong laser polarization control of coherent phonon excitation in van der Waals material Fe3GeTe2

The transient reflectivity spectra under 0° (a) and 90° (b) pump polarizations. c Comparison of the simulated coherent phonon oscillation under 0° and 90° laser polarizations. d Numerical fitting of transient reflectivity data under 0° laser polarization with coherent phonon frequency extracted from 90° polarization case. The coherent phonon frequency different under two different pump polarizations is unambiguous.