Polaritons, quasiparticles resulting from strong light-matter coupling, have become a subject of intense interest due to their potential for both fundamental research and technological applications. Among them, phonon-polaritons (PPs) arise when electromagnetic radiation strongly couples to lattice vibrations, offering powerful capabilities for manipulating the properties of quantum materials and advancing terahertz (THz) photonics. Despite their importance, conventional methods for probing PPs, such as Raman spectroscopy and transient grating techniques, often rely on finely tuned experimental conditions or intricate phase retrieval processes, which limit their accessibility and general applicability. In this chapter, we introduce and experimentally demonstrate a time-of-flight (ToF)–based technique for characterizing broadband phonon-polaritons. By launching PPs resonantly using intense THz pulses and detecting their propagation dynamics through time-resolved second harmonic generation (SHG), we are able to directly measure the ToF for individual spectral components. This, combined with measurements of PP attenuation, enables us to extract both the real and imaginary components of the dispersion relation. We apply this approach to two van der Waals antiferromagnets, NiI \(_2\) and MnPS \(_3\) , uncovering signatures of a previously hidden magnon–phonon interaction. Our method offers a broadly applicable and non-invasive route for investigating polaritonic dynamics in complex materials, and it paves the way for deeper explorations of light–matter coupling phenomena in low-dimensional and correlated systems.