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The relaxation of free holes and electrons in highly compensated germanium doped by gallium (p-Ge:Ga:Sb) and antimony (n-Ge:Sb:Ga) has been studied by a pump-probe experiment with the free-electron laser FELBE at the Helmholtz-Zentrum Dresden-Rossendorf. The relaxation times vary between 20 ps and 300 ps and depend on the incident THz intensity and compensation level. The relaxation times are about...
Transitions between the 1s and 2p levels of the fundamental heavy-hole exciton in GaAs quantum wells, followed by scattering into the 2s state, are investigated by resonant THz excitations using a free-electron laser. We report on the external control of this intra-excitonic population transfer by an external magnetic field.
The goal of our work was to study the capability of field effect transistors to measure high power THz radiation at frequencies from 0.1 up to 3 THz and to determine the linear detection limits. We observed different types of the photoresponse dependence on the incident radiation power. We qualitatively explain the unusual sub-linear behavior observed in high intensities.
We present an ultrafast terahertz detector suitable for wavelengths from 30 µm to 220 µm, which is based on a graphene flake. A logarithmic-periodic antenna is used to couple the radiation to the flake. The detector, characterized by a fast rise time combined with room temperature operation, is well suited for determining timing differences of THz laser pulses.
I will briefly review the history of THz free-electron lasers (FEL) as versatile sources for semiconductor spectroscopy and present some recent experiments using the FEL in Dresden.
We have build THz multilayer mirrors based on fabricated z-cut quartz wafers of 25 mm diameter. Using THz time-domain spectroscopy initial measurements show that the mirror reflectivity can be tuned at least up to 98.6%. We also observed cavity modes in a THz cavity made from such mirrors.
Propagation of terahertz surface plasmon polaritons along plane metal-dielectric interfaces and their jumps across air gaps have been studied using monochromatic radiation of Novosibirsk free electron laser.
We demonstrate in the experiment and simulations that interference between two contributions into the terahertz wave generation in a femtosecond filament, namely, the free electron photocurrent and the nonlinear polarization of neutrals, can be used for the femtosecond coherent control of the THz spectra.
The user FELIX Facility Nijmegen offers four FEL beam lines, FLARE from 0.2 to 3 THz, FELIX-2 from 12 to 75 THz, FELIX-1 from 2 to 12 THz and FELICE, a special beam line for intra-cavity experiments from 3–75 THz
One-pulse spectroscopy is used for the first time for a direct diagnostics of separate free-electron laser pulses. Full pulse coherency in a stabilized NovoFEL regime was demonstrated. Generation at different side-band modes in different pulses was observed when stabilizing detuning between electron and light pulses was decreased.
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