Detail Project and Funding

Abstract: The terahertz spectrum spans the frequency range from 0.1 to 10 THz corresponding to the wavelength interval from 30 to 3000 μm. At present the terahertz range is largely unexplored and the reason for this ‘terahertz gap’ is the lack of efficient and compact sources or sensitive detectors. Sources for the terahertz region exist, but they are either bulky, expensive or operate only at cryogenic temperatures, and either suffer from low output powers (<100uW) or require special conditions of temperature and humidity. In recent years, one of the most significant developments in semiconductor physics has been the emergence of a new class of emitters and detectors based on intersubband transitions. Such devices, in particular quantum cascade lasers (QCLs) operate actually in both mid- and far-infrared regions of the electromagnetic spectrum and are the most efficient compact semiconductor source in the 3-24 μm range. However, QCL technology is far from maturity and needs significant improvements in the spectral region >100 μm. In this range, the population inversion mechanisms, the optical gain, the optical confinement, the dynamics of the electron-phonon interaction and the electronic distribution have to be too much intensively analyzed to extend QCL operation at higher temperature and longer wavelengths. In addition, the peculiar versatility of the design offered by the bandgap engineering makes this source an ideal tool for the realization of mode-locking or metrological-grade semiconductor micro-sources in the far infrared, not existing so far.
Quantum cascade lasers can have a real impact in technological applications such as homeland security, pollution monitoring, process control, countermeasures and clinical diagnostics. In this aspect they also have a huge potential for improvements in the quality of life. In addition to applications, there is considerable interest in intersubband processes and related optoelectronic phenomena from a fundamental physics viewpoint.
The present proposal will make a step-change in the research on THz quantum cascade laser (QCL) and related fundamental physical phenomena. We plan to improve the laser performance in order to come up with advanced devices and novel set-ups based on non-linear optical techniques employing advanced models for the understanding of the physics of intersubband emitters. In addition through ground-breaking research on both the fundamental and applied aspects of THz QCL
design and implementation, we will develop the next generation of QCL technology that is defined by, and can be employed by the European Photonics platform.
The proposal will be built on these foundations to explore new physical concepts, towards enhancing the performance, the functionality, the stabilization and the integration with novel optical components (high efficiency waveguides and nano-structured detectors) of compact semiconductor THz sources via a collaborative research across a broad range of disciplines including: advanced nano-fabrication, high resolution spectroscopy, optical metrology, holographic imaging, non-linear optics and advanced solid state theory.
The major aim of the research proposal is the development of:
i) reliable THz QCL devices operating at Peltier cooler temperatures, with progressively higher output powers, quantum efficiency, tunability;
ii) THz QCL with high directional beam profiles, coupled with high efficiency and low transmission losses to THz optical waveguides;
iii) Nano-structured detectors in a single pixel or array configuration coupled with high peak power THz QCLs;
iv) Optical set-ups aimed to holographic imaging experiments in the far infrared;
v) New optical set-ups based on high-resolution THz spectroscopy and non-linear up-conversion techniques enabling ultra-narrow, metrological-grade THz
micro-source;
vi) Original advanced models for the understanding of the physics of intersubband phenomena.
The successful achievement of the project objectives aims to the establishment of an Italian scientific network of excellence in the field of innovative THz sources that will play a strategic role for the Italian and European technological progress, in application fields as homeland security, cultural and environmental heritage and medial diagnostics

INO’s Experiments/Theoretical Study correlated:
Synthesis of terahertz frequencies by optical frequency mixing
Cavity-enhanced THz molecular spectroscopy