TeraHertz (THz) waves (1-10 THz) are non-ionizing radiation that can potentially find applications in a variety of domains. The most promising at this time are THz imaging – as a variety of important materials (plastics, ceramics) are transparent – and spectroscopy since T-rays interact with matter with unique fingerprints. Although there have been many technological advances both academically and in industry, there is currently no practical amplifiers of THz radiation available.
Internship Subject :
Although quantum cascade lasers (QCLs), novel sources based on intersubband transitions, operate in the THz frequency range, QCL-based amplifiers cannot be reliably implemented because it is exceedingly difficult to implement anti-reflection coatings for the laser facets. Hence, a vertical geometry appears to be a potential solution for a THz amplifier. However, vertical emission cannot be directly exploited in QCLs because intersubband transitions are only coupled to transverse magnetic (TM) waves, i.e. with electric field perpendicular to the surface. A solution is to implement sub-wavelength diffractive structures, like photonic crystals or metasurfaces, to couple a normal incident wave to TM waves in the active medium (see below figure). Following this analysis, the goal of this project is to realize a broadband Vertical Cavity Semiconductor Optical Amplifier (QC-VCSOA) based on a THz QCL structures. It will consist of an active medium made of an electrically pumped microstructured semiconductor/metal heterostructure. This proposal will be based on the engineering the bandstructure of QCLs for broad spectral gain and its refractive index dispersion to realise new structures for the amplification of short THz pulses. The potential student will acquire skills in design of complex quantum and electromagnetic structures, and an experimental background in condensed matter and ultrafast physics in newly accessible spectral regions.
Condensed matter physics ; Experimental photonics ; THz spectral region ; Ultrafast Physics