Importance of Terahertz light
The excitation lines of many molecules lie within the terahertz spectral region. Many industrial and scientific applications in
atmospheric science
biological and medical sciences
astrophysics
security screening and illicit material detection
non-destructive evaluation
communications technology
ultrafast spectroscopy etc.
exploit these excitation lines. For this purpose, coherent and intense Terahertz light emitting devices are essential.
Motivation - closing the Terahertz gap
In spite of the wide scope of possible applications, there are no efficient Terahertz laser that operate at room temperature.
In fact, it is common to speak of the "Terahertz gap":
The Terahertz gap defines the electromagnetic spectral region of 0.1-10 THz (C. Sirtori Nature 417, 132(2002)).
So far, there are no efficient coherent light sources that emit at room temperature within this spectral region.
Promising candidate: Terahertz quantum cascade laser
Calculated spectral function and energy resolved density in two periods of a typical resonant phonon Terahertz quantum cascade laser
Quantum cascade lasers (QCLs) consist of periodically repeated semiconductor layers of typical widths around 1-15nm.
Electrons within QCLs face quantum mechanical effects such as
interference, tunneling, and confinement. In addition,
the electrons
scatter on lattice vibrations, impurities, rough interfaces etc.
Therefore, Terahertz QCLs are mesoscopic devices at the border between the nanometer scaled coherent quantum mechanics and the typically
long ranged phase breaking scattering.
Projects in this area:
Implementation of nonequilibrium Green's function formalism on transport and gain in THz-QCLs
Analysis of the relative importance of coherent transport and various scattering mechanisms in THz-QCLs (Journal of Physics: Conference Series 193, 012026 (2009),
Phys. Rev. B 79, 195323 (2009))
Identification of adverse non-periodic effects in THz-QCLs (Journal of Physics: Conference Series 193, 012063 (2009))
Conceptional improvement of THz-QCL designs (Appl. Phys. Lett. 97, 261106 (2010))
Experimental collaborations
Hamamatsu Photonics (Japan), Central Research Laboratory
Technical University of Vienna (Austria), Institut für Photonik
Nanyang Technological University, Singapore
Technische Universität München (Germany), Department of Electrical Engineering and Information Technology
University of Tokyo (Japan), Department of Industrial Science, Informatics and Electronics
Group Members Involved:
