Colloquia & Guest Speakers

Ultra-broadband "white light" terahertz pulses - generation, detection, and spectroscopy

Hartmut Roskos, Johann-Wolfgang-Goethe-Universität, Frankfurt, Germany

Monday, September 22, 2014
3 p.m.–4:30 p.m.

Goergen 101, Sloan Auditorium

The last years have seen tremendous advances in the capability to generate and detect ultrashort pulses in the FIR-to-mid-IR spectral range using frequency mixing and rectification of femtosecond pulses from NIR table-top laser systems. The target frequencies correspond to photon energies from 0.4 to 600 meV, which allow to excited and probe many primary electron, phonon and correlation processes in solids (but not only there). With widening bandwidth, the time resolution now reaches into the femtosecond regime even in this longwavelength spectral regions, which permits to trace ultrafast phenomena with unprecedented time resolution and wide spectral coverage. Field strengths reach into the tens of MV/cm range and open the way to novel nonlinear phenomena.
This presentation gives a general overview of the most important techniques of generation and detection of ultra-broadband THz/IR pulses. Special emphasis is given to approaches which use laser-generated air plasmas, and to detection with a sum-frequency XFROG technique (XFROG: cross-correlation frequency-resolved optical-gating) which enables to cope with the tremendous bandwidth available. Examples of spectroscopic applications are given, among others studies of relativistic Doppler reflection in photo-excited silicon.

Nick Usechak headshotHartmut Roskos was born in Freiburg, Germany in 1959. He received his diploma in Physics from the Technical University in Munich as well as his Ph.D., where his dissertation focused on charge carrier relaxation in Germanium with sub-picosecond light pulses in the infrared. He worked as Postdoc at Bell Labs, as research assistant and as chief scientist at RWTH in Aachen, Germany prior to accepting a position in 1997 as full professor at the Johann-Wolfgang-Goethe-Universität in Frankfurt, Germany. He currently spends a sabbatical at the University of Rochester, collaborating with Prof. Zhang. to investigate ultra-broadband THz spectroscopy of plasmons in graphene structures and of the Higgs mode in superconducting thin films.