Ultrashort strain soliton formation in sapphire and ruby

We discuss the development of ultrashort strain solitons in sapphire and ruby using Brillouin spectroscopy and numerical results of the Korteweg–de Vries equation. We demonstrate that solitons are formed in unexcited ruby, showing no significant difference with sapphire in phonon properties in the frequency regime under study. Further, the role of the radiative tail in the evolution of the low-frequency Brillouin spectrum is investigated. It is shown that its influence on the typical oscillation pattern is limited, confirming our earlier interpretation in terms of Bragg reflections and spatial resonances of the soliton train.