Graphene is a promising material for optoelectronics and photonics. Recent experiments demonstrated graphene
photodectectors based on interband transitions working at Mid and Near-IR/Visible regions. Extension of spectral
range to longer wavelengths requires alternative photoresponse mechanisms. One of the mechanisms which has
been proven to be efficient for THz detection in "classical" semiconductor materials is the optically-induced
breakdown of quantum Hall effect. In our work we successfully demonstrated a graphene-based QHE
photodetector. Our result demonstrates the potential of graphene as a material for Far-IR photodetectors. Further
improvement in device design and use of more efficient radiation coupling solutions should enable graphene
photodetectors with broader spectral range, higher sensitivity, and elevated operating temperatures for a variety of
We demonstrated that coherently driven atomic or molecular media potentially yield strong controllable short pulses of THz radiation. The method is based on excitation of maximal coherence in an atomic or molecular gas by optical pulses and coherent scattering of infrared radiation to produce pulses of THz radiation. The pulses can reach the energies ranging from seeral nJ to μJ and time durations from several cycles to ns at room temperature.
A new type of accessible source of ultrashort optical pulses, based on the phenomenon of collective coherent recomination (superfluorescence) of electrons and holes in semiconductor heterostructures is proposed. The novel regime of an ultrafast operation of quantum-well semiconductor lasers with a low-Q cavity of length approximately 30 $min 100(mu) is analyzed, in which a quasiperiodic sequence of superradiant pulses of duration up to 30 fs and peak intensity exceeding 100 MW/cm<SUP>2</SUP> is emitted under continuous pumping, with typical current density of order 10<SUP>4</SUP> A/cm<SUP>2</SUP>. It is shown that the same process of femtosecond superradiant recombination can be used for the room-temperature generation of optical coherent emission in multiple quantum-well or quantum dot GeSi/Ge structures, employing direct radiative transitions from the T-valley.
This work reports first observation of a 2D-exciton luminescence in thin (8 - 25 nm) Ge layers of Ge-Ge<SUB>1-x</SUB>Si<SUB>x</SUB> multiple quantum well structures grown on Ge  substrates. Photoluminescence spectra was studied at temperatures 2 - 300 K using a BOMEM DA3.36 Fourier-transform spectrometer with a cooled InSb detector, and use of a Nd:YAG laser radiation ((lambda) equals 1.06 micrometers ) for excitation. The shape of the luminescence spectral lines was corrected by black body calibration of the spectrometer.