“…Moreover, these acoustic waves can couple to fast relaxation dynamics, the characteristic frequency of which is in the GHz~THz range. Previous Brillouin scattering studies on aspirin [ 17 , 18 , 19 ], ibuprofen [ 20 , 21 , 22 ], acetaminophen [ 23 ], and other pharmaceuticals [ 24 , 25 , 26 ] revealed clear anomalies near the glass transition temperatures ( T g ) and fast relaxation processes that coupled to the longitudinal acoustic waves. The present study is aimed at investigating and comparing acoustic properties of progesterone in its glassy, ultraviscous, crystalline, and liquid states.…”