Abstract
We have developed terahertz (THz) quantum-cascade lasers (QCLs) based on GaAs/AlAs heterostructures for application-defined emission frequencies between 3.4 and 5.0 THz. Due to their narrow line width and rather large intrinsic tuning range, these THz QCLs can be used as local oscillators in airborne or satellite-based astronomical instruments or as radiation sources for high-resolution absorption spectroscopy, which is expected to allow for a quantitative determination of the density of atoms and ions in plasma processes. The GaAs/AlAs THz QCLs can be operated in mechanical cryocoolers and even in miniature cryocoolers due to the comparatively high wall-plug efficiency of around 0.2% and typical current densities below 500 A/cm $^2$ . These lasers emit output powers of more than 1 mW at operating temperatures up to about 70 K, which is sufficient for most of the abovementioned applications.
Highlights
T HE invention of quantum-cascade lasers (QCLs) about 25 years ago [1] opened the path to a variety of spectroscopic approaches in the mid- to far-infrared spectral region
Since 2014, a THz QCL developed at the Paul-Drude-Institut has been employed as the local oscillator on board of Stratospheric Observatory For Infrared Astronomy (SOFIA) for the detection of interstellar atomic oxygen [6]
QCLs emitting in the atmospheric windows around 3.43, 4.32, and 4.92 THz are of interest for applications such as THz spectroscopy under pulsed megagauss magnetic fields at high-magnetic-field facilities, if the THz radiation has to be transmitted through air over a distance of about 10 m into the magnet inside a Faraday cage
Summary
T HE invention of quantum-cascade lasers (QCLs) about 25 years ago [1] opened the path to a variety of spectroscopic approaches in the mid- to far-infrared spectral region. QCLs for the terahertz (THz) spectral region [2] allow for high-resolution spectroscopy of molecules, atoms, and ions utilizing rotational or fine-structure transitions. The rotational transition of OH at 3.55 THz and the fine-structure line of atomic oxygen (OI) at 4.75 THz are of particular interest Both can be measured with QCL-based heterodyne receivers. QCLs emitting in the atmospheric windows around 3.43, 4.32, and 4.92 THz are of interest for applications such as THz spectroscopy under pulsed megagauss magnetic fields at high-magnetic-field facilities, if the THz radiation has to be transmitted through air over a distance of about 10 m into the magnet inside a Faraday cage Due to their high emission powers and narrow line widths in continuous-wave (cw) operation, THz QCLs are excellent radiation sources for high-resolution spectroscopy. We demonstrate the operation of these THz QCLs in a mechanical cryocooler (Ricor K535) or a miniature cryocooler (AIM SL400)
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