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Investigating the formation and decay time of excitons by ultrafast spectroscopy

Excitons term the bound states of electrons and holes in semiconductor materials. The binding energy of these states and the energy of intraexitonic transitions correspond to the Terahertz frequency area. In order to examine the dynamic of excitons in semiconductors different probes are optically excited with a broadband query pulse. The experiments are conducted with the femtosecond amplifier system of the research group. The laser pulses of the amplifier system, which are 35 femtoseconds short, are separated by a beam splitter in the query beam and response beam. The focal wavelength of the optical excitation pulse is adjustable via an optical parametric amplifier in the range of 565 nm to 2700 nm. Through optical rectification on a non-linear crystal, the broadband terahertz query pulses are created and the timely distance of query and response pulse is also adjustable.

The main objective of the experiment ist the examination of the creation process of excitonic states and their dynamics. A special geometry is used to examine the bound state of spatially separated electrons and holes for the first time.

Contacts:Philipp Richter or Prof. Dr. Martin Koch