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The use of a high-electron mobility semiconductor nanowire as transistor channel has recently allowed the extension of the spectral coverage of THz field-effect transistor detectors up to 1.5 THz. In this report, we demonstrate efficient operation of a field-effect transistor detector based on a semiconductor nanowire at a much higher frequency, 2.8 THz, with a responsivity ?5 V/W in a bandwidth ?100 kHz, thus proving the full potential of such approach for the detection of THz quantum cascade lasers. Finally, such a THz sensing system is exploited to perform raster scan transmission imaging, with high spatial resolution, signal-to-noise ratio, and acquisition rate. © 2014 AIP Publishing LLC.

We report on the evidence of saturation effects in a rotational transition of CH3OH around 2.5 THz, induced by a free-running continuous-wave quantum cascade laser (QCL). The QCL emission is used for direct-absorption spectroscopy experiments, allowing to study the dependence of the absorption coefficient on gas pressure and laser intensity. A saturation intensity of 25 mu W/mm(2), for a gas pressure of 17 mu bar, is measured. This result represents the initial step towards the implementation of a QCL-based high-resolution sub-Doppler THz spectroscopy, which is expected to improve by orders of magnitude the precision of THz spectrometers. (C) 2015 AIP Publishing LLC.

Tuning of the emission wavelength in GaAs/AlxGa1-xAs bound-to-continuum quantum cascade lasers with different Al mole fractions (x) is reported. By varying x in the range of 0.37-0.52, a shift of the emission wavelengths of over 4 mu m has been observed. Using this method, laser action in the range of 11.2-15.3 mu m at temperatures T >= 260 K has been demonstrated with a record value of similar to 340 K for GaAs based QCLs operating at 13.5 mu m. (C) 2008 American Institute of Physics.