We report the polarization, the interference far-filed pattern, the multimodal spectral emission and the power extraction of the emitted beam from a set of electrically-pumped random quantum cascade lasers in the terahertz range. By integrating, on chip, a non-linear multilayer graphene stack with the laser gain medium, we demonstrate self-induced phase-coherence between the naturally incoherent random modes. We then employ the devised random laser in a detectorless near-field imaging system, exploiting the intracavity reinjection of the laser field via self-mixing interferometry in a confocal microscope for speckle-free tomography with nm-size resolution
We measured the nonlinear response of field effect transistors fabricated with GaAs-based heterostructures by
performing direct detection, heterodyne and subharmonic mixing measurements. The study of the spectral responsivity
as a function of different antenna coupling is presented in the 0.18-0.4 GHz range. We also verified the subharmonic
and heterodyne mixing at 0.6 THz in a HFET detector with a broadband antenna.
We present the realization of high electron mobility transistors on GaN-heterostructures usable for mixing and rectification in the THz range. Device fabrication is fully compatible with industrial processes employed for millimetre wave integrated circuits. On-chip, integrated, polarization-sensitive, planar antennas were designed to allow selective coupling of THz radiation to the three terminals of field effect transistors in order to explore different mixing schemes for frequencies well above the cutoff frequency for amplification. The polarization dependence of the spectral response in the 0.18-0.40 THz range clearly demonstrated the possible use as integrated heterodyne mixers.
We studied mid-infrared sensors based on the wavelength shift of Surface Plasmon Polariton resonances upon solid
substance deposition on subwavelength hole arrays in a thin metal film (metal meshes). We present an experimental and
numerical investigation of the mid-infrared transmission of metal meshes with and without a dielectric substrate, and we
develop an analytical model which describes the Fano interference between the Bethe continuum and the SPP
resonances. Fitting the differential transmission signal, measured before and after deposition of a target solid film, we
demonstrate sensitivity down to few molecular monolayers, at least one order of magnitude better than mid-infrared
vibrational spectroscopy. Sensor calibration was performed on thin polymer films and an example of real application is
then provided by measuring the optical density of phospholipid membrane complexes with thickness in the range 2-10
nm.
Imaging arrays of direct detectors in the 0.5-5 THz range are being experimentally developed. Terahertz active imaging
with amplitude-modulated quantum cascade lasers emitting at 2.5 and 4.4 THz performed by using an antenna-coupled
superconducting microbolometer. We then present two room-temperature terahertz detector technologies compatible
with monolithic arrays: i) GaAs Schottky diodes with air-bridge sub-micron anodes; ii) high electron mobility transistors
with sub-micron Schottky gate. Performances, requirements and fabrication costs of the different detector technologies
are compared.
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