The FLASH collaborations recently published two contributions available open access in Optics Express:
- C. Ciano et al. discussing photoluminescence in n-type Ge/SiGe quantum wells that are optically excited using a free-electron laser. Photoluminescence is observed at 4 THz, which can be related to an optical transition from the third to second levels in a coupled quantum well, with the possible of the second-to-first level transition also contributing to the emission. This work offers promising advances towards ultimately realizing electrically-injected, silicon-based quantum cascade lasers operating at THz frequencies.
- K. Gallacher et al. reporting on the waveguide losses for a range of surface plasmon and double metal waveguides in Ge/Si1−xGex THz quantum cascade laser gain media at 4.79 THz (62.6 µm wavelength). The results demonstrate losses comparable to similar designs of GaAs/AlGaAs quantum cascade laser plasmon waveguides indicating that a gain threshold of 15.1 cm−1 and 23.8 cm−1 are required to produce a 4.79 THz Ge/SiGe THz laser at 10 K and 300 K, respectively, for 2 mm long double metal waveguide quantum cascade lasers with facet coatings.