Dr. Karl Unterrainer, Technische Universität Wien
" Few Cycle and Non-linear THz-Spectroscopy of Semiconductors"


Ultrashort optical pulses incident on semiconductor surface generate few cycle THz pulses. This generation is attributed to optical rectification and transient field screening. We have found a new emission process which is based on plasmon emission of cold extrinsic carriers. These carriers are excited by the transient field screening at the surface and start to oscillate at their Eigenmode which is the plasma frequency. We observe long damping times and a significant increase of the emission efficiency.
Applications in the spectroscopy of nanostructures (time domain spectroscopy, optical pump and THz probe) will be presented.