We shall investigate in collaboration with BNL electron and phonon relaxation processes in strongly correlated electron systems such as cuprate high-temperature superconductors. The dynamics of photoexcited electrons and photoinduced lattice expansions, measured by ultrafast (femtosecond) time-resolved spectroscopy at BNL, will be analysed in the framework of our theory of hot electron relaxation in metallic compounds. Using the exact analytical solutions of the kinetic equations and experimental relaxation times, we are aiming to resolve a controversial issue concerning whether the electron-phonon interaction is crucial, or else weak and inessential in novel superconductors.