Figure 4: RF modulation effects on terahertz emission spectra.
From: Homogeneous spectral spanning of terahertz semiconductor lasers with radio frequency modulation
Emission spectra of the terahertz QCL measured at 580 (a), 700 (b), 900 (c), and 1100 mA (d). The black curves are taken when the laser is in free-running mode, and the red ones are the results obtained with the RF modulation. The horizontal dashed lines show the −20 dB level. (e) The water absorption lines in the frequency range from 3.9 to 4.4 THz extracted from the HITRAN database.
