Ultra-broadband THz pulses — From millimeter waves to the infrared

This presentation gives an overview of the most important approaches towards the generation of ultra-broadband THz pulses. Special emphasis is then given to the coherent detection of the pulses which becomes an ever more challenging task the larger the bandwidth of the pulses is. Detection with laser-induced gas plasmas and via a sum-frequency XFROG (cross-correlation frequency-resolved optical-gating) technique are discussed. In the third part of the presentation, examples of spectroscopic applications of such pulses are given. They find use either for the intensive excitation of materials in nonlinear spectroscopy, or for the probing of transient phenomena with a very good time resolution and covering a wide spectral range; highly useful, for example, for the investigation of materials with strong electronic correlation, in order to monitor the temporal evolution of electronic and phononic degrees of freedom.