Pump-probe spectroscopy in the infrared

We discuss infrared pump-probe spectroscopy experiments, where both tabletop lasers and a free-electron laser are applied as radiation sources covering the inire infrared range from the near infrared to terahertz.The focus of the talk is on the basic principle of the experiment and related techniques like four-wave mixing, and on the experimental capabilities in our labs at HZDR. Electronic transitions in semiconductor quantum wells, interband transitions in graphene, plasmonic excitations in graphene ribbons will serve as examples for low-energy excitations that can be investigated in a time-resolved manner. In particular, examples for excitations with different polarization states will be discussed. Finally we will show the strength of probing with terahertz time-domain spectroscopy.