Terahertz Quantum Cascade Lasers

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":

    Terahertz gap, taken from Carlo Sirtori Nature 417, 132(2002)

    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

    LDOS and energy resolved density at laser threshold

    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: