Ultrabroadband terahertz (THz) radiation is a useful and versatile tool in the fields of spintronics and ultrafast magnetism. THz emission spectroscopy exploits this radiation as a direct probe: a metallic heterostructure is excited with a femtosecond optical pulse, and the resulting sub-picosecond charge-current dynamics are read out through the emitted THz field, giving access to spin transport on femtosecond timescales.