Towards efficient and tunable generation of THz radiation from quantum dot based ultrafast photoconductive antennae

We present our recent results on CW and pulsed THz generation in quantum dot(QD) based photoconductive antennae(PCA) pumped by ultrafast and dual wavelength semiconductor lasers. QDPCA substrate incorporates InAs QDs in GaAs matrix, thus keeping semiconductor carrier mobility at higher levels that is typical for SI GaAs, while QDs themselves serve as lifetime shortening centres, allowing to achieve subpicosecond operation as in LT-GaAs. Thus, such substrates combine the advantages and lacking the disadvantages of GaAs and LT-GaAs, which are the most popular materials so far, and thus can be used for both CW and pulsed THz generation. Moreover, by changing QD size and mutual allocation, effective pump wavelengths can be tuned in the range between 0.9-1.3 μm, which is well beyond the GaAs energies, hence compact and relatively cheap ultrafast and narrow line double-wavelength semiconductor and fibre pump lasers can be used for pumping such antennae for both pulsed and CW THz generation. For double wavelength operation of semiconductor lasers, we implement either stacked double volume Bragg gratings, or double-Littrow configuration with two independent diffraction gratings to achieve tunability of the generated THz signal. High thermal tolerance of QD wafers allowed pumping single-gapped antennae with lasers producing up to 250 mW of CW optical power at simultaneous double wavelength operation and up to 1W average optical power in pulsed regime. We show these QD based antennae combined with such pump lasers to generate pulsed and CW THz radiation that is superlinearly proportional to pump power and bias applied to antenna.