Photodetectors made from graphene can process and conduct light signals as well as electric signals extremely fast. Within picoseconds the optical stimulation of graphene generates a photocurrent. Until now, none of the available methods were fast enough to measure these processes in graphene. Scientists at the Technische Universitaet Muenchen now developed a method to measure the temporal dynamics of this photo current. Furthermore they discovered that graphene can emit terahertz radiation.