Thecreationandpropagationoflongitudinalacousticphonons(LAPs)inhighqualityhematitethinfilms(α-Fe2O3)epitaxiallygrownondifferentsubstrates(BaTiO3,SrTiO3,andLaAlO3)areinvestigatedusingthefemtosecondpump–probetechnique.Transientreflectionmeasurements(?R/R)indicatethephoto-excitedelectrondynamics,andtheinitialdecaylessthan1psandtheslowdecayof～500psareattributedtotheelectron-LOphononcouplingandelectron–holenonradiativerecombination,respectively.LAPsinα-Fe2O3filmcanbecreatedbyultrafastexcitationoftheligandfieldstate,suchastheligandfieldtransitionsunder800-nmexcitationaswellastheligandtometalcharge-transferwith400-nmexcitation.Thestrainmodulationsofthesoundvelocityandtheout-of-planeelasticpropertiesaredemonstratedinα-Fe2O3filmondifferentsubstrates.
