Abstract

We report the generation of tuneable THz radiation (0.75-3 THz) through second order nonlinear effects in the excitation of excitons in GaAs/AlAs multi-quantum wells (MQWs), using readily available continuous wave (CW) laser diodes at room temperature. A MQW GaAs/AlAs sample was designed to have excitonic resonances at a wavelength accessible by commercially available lasers (850nm, 260mW), and have E1HH1–E1LH1 splitting of 9.1meV. The sample was grown by MBE with the MQW region containing 30 repeats of 11.9nm GaAs separated by 7.1nm AlAs barriers. These preliminary measurements removed the substrate and cap layer. The sample was then capillary bonded to a diamond heat spreader [1]. Two collimated lasers were used to excite the excitonic resonances. Both lasers were normally incident to the sample surface. Figure 1(a) shows THz power obtained in collinear and crossed polarisations of the lasers with one laser resonant with the HH exciton, and the other laser tuned across the excitonic bands with both lasers operating at 260mW. A clear signal is observed in the case of collinear excitation which scales with the density of states of the excitons. Power dependence measurements confirm this is a second order non-linear effect. Using a simple interferometer, and fitting the measured power with the expected transmission of a Fabry-Perot etalon, frequency measurements indicate the ability to tune the THz radiation from 0.75-3THz. See Figs 1(b-d). For excitation at the peaks of HH and LH, a conversion efficiency of 1.2×10⁻⁵ was obtained. This was achieved without the use of plasmonic effects, nor any kind of an antenna, nor an applied E-field to the structure. This offers the opportunity for the creation of compact, low cost, tuneable room temperature THz source.

© 2017 IEEE