We present recent work towards the realization of a nanowire-based terahertz quantum cascade laser. Nanowires offer an additional quantum mechanical confinement of electrons in the plane of a two-dimensional quantum cascade structure. The additional quantization can greatly increase the lifetimes of intersubband transitions and therefore increase the optical gain and also the maximum operating temperature of terahertz quantum cascade lasers. We outline a fabrication process that is fully scalable from nanowire to micropillar devices and present measurements of micropillar arrays in a double metal waveguide. The results are very promising and also show the main technological challenges for realizing nanowire-based devices.
We present the realization of active photonic crystal terahertz lasers operating in higher photonic bands. The
resonator consists of an array of isolated pillars which are embedded in a metallic waveguide. These devices
reduce the overlap with gain region and increase the effect of the surrounding medium. Thereby, it is either
possible to directly manipulate the lasing mode or to sense variations in the environment.
This presentation introduces a chemical analyzer (The ERACHECK) which is based on quantum cascade laser
technology for measuring oil-in-water. Using these mid-IR lasers, it was possible to develop a portable, robust and
highly precise analyzer for the measurement of oil-in-water, a parameter which is vital in the petrochemical industry for
process control and environmental analysis. The overall method employs a liquid-liquid extraction step of the aqueous
sample using a cyclic, aliphatic hydrocarbon such as cyclohexane. Quantification is based on measurement of the C-H
deformation vibrations of the extracted hydrocarbons in the cyclic extraction solvent. The developed method is linear
from 0.5 - 2000 ppm of oil in water, with precisions well below 15% in terms of r.s.d for repeated measurements. The
portability of the ERACHECK and its robustness has been key for its successful use on oil rigs as well as petrochemical
production sites on land. The values provided by the ERACHECK correlate well with those obtained by the former CFC
(Freon 113) based method for oil in water, which is no longer in use in industrialized countries due to the ozone
depleting effect of the CFCs employed.
We present a new waveguide concept for terahertz quantum-cascade laser. The double-metal waveguide confines the active region between two metallic layers. Thereby, a modal confinement of almost 100 % is achieved. However, these metal layers are also one of the dominating loss mechanisms. Replacing the conventional metal with a superconductor helps to reduce the total losses. A surface plasmon is formed at the interface between the superconductor and the semiconductor. It can be maintained even for photon energies above the superconducting band gap. In this work we use niobium with a band gap of 2.8 meV to confine the active region of a THz-QCL emitting at 9 meV.
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