The gain recovery time of a heterogeneous active region terahertz quantum cascade laser is studied by terahertz-pump-terahertz-probe spectroscopy. The investigated active region, which is based on a bound-to-continuum optical transition with an optical phonon assisted extraction, exhibits a gain recovery time in the range of 34–50 ps dependent on the operation condition of the laser. The recovery time gets shorter for stronger pumping of the laser while the recovery dynamics slows down with increasing operation temperature. These results indicate the important role of the intracavity light intensity for the fast gain recovery.
A new publication by CoQuS student Christian Derntl of the Unterrainer group!
THz-pump/THz-probe spectroscopy for the assessment of the gain recovery time in a THz QCL: (a) schematic of the optical setup and the modulation scheme; (b) amplitude of the THz-probe, which is generated in the integrated emitter for the THz-pump at 0 ps, is plotted as a function of the pump-probe delay time (PPD); (a) and (c) THz pulses and the spectral content of the THz pulses after the propagation through the QCL section.