In this talk, I will give an overview of my PhD thesis, focusing on two topics: lattice dynamics in black phosphorus and ultrafast energy flow in 3d
ferromagnets. The layered semiconductor black phosphorus exhibits a peculiar structure with in-plane anisotropy. Here, we use femtosecond electron diffraction to access the lattice response to laser excitation. The optical excitation and subsequent electron-phonon coupling lead to a pronounced non-thermal state of the lattice, which is characterized by a transiently reduced anisotropy of the atomic vibrations. On timescales of tens of picoseconds, thermal equilibrium is restored via phonon-phonon coupling [1,2]. Our results yield insights into both electron-phonon and phonon-phonon coupling and provide pathways to control the timescale of lattice thermalization in black phosphorus.